Substitution Of Leucine Research Articles

Synonymous mutation gene design to overexpress ACCase in creeping bentgrass to obtain resistance to ACCase-inhibiting herbicides.

Overexpression of a native gene can cause expression of both introduced and native genes to be silenced by posttranscriptional gene silencing (PTGS) mechanisms. PTGS mechanisms rely on sequence identity between the transgene and native genes; therefore, designing genes with mutations that do not cause amino acid changes, known as synonymous mutations, may avoid PTGS. For proof of concept, the sequence of acetyl-coA carboxylase (ACCase) from creeping bentgrass (Agrostis stolonifera L.) was altered with synonymous mutations. A native bentgrass ACCase was cloned and used as a template for the modified gene. Wild-type(WT) and modified genes were further modified with a non-synonymous mutation, coding for an isoleucine to leucine substitution at position 1781, known to confer resistance to ACCase-inhibiting herbicides. Five-hundred calli of creeping bentgrass 'Penn A-4' were inoculated with Agrobacterium containing either the WT or modified genes, with or without the herbicide-resistance mutation. Six herbicide-resistant-transgenic events containing the modified gene with the 1781 mutation were obtained. Transcription of the modified ACCase was confirmed in transgenic plants, showing that gene-silencing mechanisms were avoided. Transgenic plants were confirmed to be resistant to the ACCase-inhibiting herbicide, sethoxydim, providing evidence that the modified gene was functional. The result is a novel herbicide-resistance trait and shows that overexpression of a native enzyme with a gene designed with synonymous mutations is possible.

117P Classification of EGFR mutations in Pakistani lung adenocarcinoma for predicting response to targeted therapy

Lung cancer is the 4th leading cause of death in all cancers. Adenocarcinomas of lung constitute up to 50% of NSCLC. In Pakistan like rest of the world lung cancer prevalence is high (15%) and primary lung adenocarcinoma constitute about 40–45% of primary lung cancer. Mutations in EGFR tyrosine kinase domain have been reported in adenocarcinoma. EGFR mutation screening has become imperative for the selection of metastatic NSCLC patients eligible for targeted treatment. This report presents distribution of EGFR mutations in 315 NSCLC patients. EGFR mutation in tumor samples was screened by multiplex real time PCR (Roche Diagnostics(R), USA) according to the manufacturer's instructions. Briefly, DNA from FFPE tissue, obtained from Histopathology sections, was extracted and amplified with primers and probes specific to 43 different EGFR mutations in Cobas z 480 instrument. The assay can detect 43 mutations in four exons (18–21) of EGFR gene, including several point mutations, deletions and insertions. Out of 315 patients, 208 were male and 107 were females; male to female ratio was 2:1. The mean age of the patients was 62 years and age distribution was 23 and 85 years. On the basis of immuno histopathological finding tumors were categorized into two groups; well to poorly differentiated adenocarcinoma 231(73%) and metastatic adenocarcinoma 84 (27%). EGFR mutation Del 19 was detected in 38 patients, its short in-frame deletion in exon 19, clustered around the amino acid resideus747–750(most common variant delL746-A750, delL747-T751insS, and delL747-P753insS). Whereas L858R point mutation (substitution of amino acid leucine to arginine) was found in 27 patients. In two patients compound mutation, two point mutations together [S768I and G719X] and another one insertion (amino acid residues inserted) on Exon 20 was observed. L858R (exon 21) and deletion 19 exon were most frequent mutations in primary lung adenocarcinoma patients of Pakistani origin, in published literature female preponderance was significant. Our study showed Del 19 and L858R were the most frequent mutations in Pakistani lung cancer patients. In additions, 25% of the patients were found eligible for targeted therapy.

Molecular Characterization of a Novel Germline VHL Mutation by Extensive In Silico Analysis in an Indian Family with Von Hippel-Lindau Disease.

Von Hippel-Lindau [VHL] disease, an autosomal dominant hereditary cancer syndrome, is well known for its complex genotype-phenotype correlations. We looked for germline mutations in the VHL gene in an affected multiplex family with Type 1 VHL disease. Real-Time quantitative PCR for deletions and Sanger sequencing of coding regions along with flanking intronic regions were performed in two affected individuals and one related individual. Direct sequencing identified a novel heterozygous single nucleotide base substitution in both the affected members tested, segregating with VHL phenotype in this family. This variant in exon 3, c.473T>A, results in substitution of leucine, a highly conserved acid, to glutamine at position 158 [p.L158Q] and has not been reported thus far as a variant associated with disease causation. Further, this variant was not observed in 50 age and ethnicity matched healthy individuals. Extensive in silico prediction analysis along with molecular dynamics simulation revealed significant deleterious nature of the substitution L158Q on pVHL. The results of this study when collated support the view that the missense variation p.L158Q in the Elongin C binding domain of pVHL may be disease causing.

Effect of alanine, leucine, and arginine substitution on antimicrobial activity against candida albicans and action mechanism of a cationic octadecapeptide derived from α-amylase of rice.

AmyI-1-18, an antimicrobial peptide, is a cationic α-helical octadecapeptide derived from α-amylase of rice (Oryza sativa L. japonica) that contains four cationic amino acid residues (two arginines and two lysines). To enhance the antifungal activity of AmyI-1-18 against Candida albicans, 11 analogs bearing substitutions with alanine, leucine, and/or arginine, which were designed on the basis of the helical wheel projection of AmyI-1-18, were synthesized, and their antifungal activity was investigated. The antifungal activities of four analogs obtained by replacing arginine or lysine with alanine were significantly reduced. The results suggested that the cationic arginine and lysine residues in AmyI-1-18 are important for its antifungal activity. The antifungal activities of two single leucine-substituted analogs were not improved, but among three single arginine-substituted analogs, AmyI-1-18(D15R) had approximately a twofold higher antifungal activity [50% growth-inhibitory concentration (IC50 ): 31 μM] than AmyI-1-18 (IC50 : 64 μM) and exhibited low hemolytic activity (4% at 100 μM). Flow cytometric analysis using propidium iodide revealed that the antifungal activity of AmyI-1-18(D15R) was dependent on its membrane-disrupting activity in a manner different from that of AmyI-1-18. Further enhancement of the cationicity and hydrophobicity of AmyI-1-18(D15R) resulted in no improvement in antifungal activity and a significant increase in hemolytic activity. In this study, the results demonstrated that the antifungal activity of AmyI-1-18 against C. albicans was enhanced through increasing its membrane-disrupting activity by replacing aspartic acid at position 15 with arginine without a significant increase in hemolytic activity. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 219-229, 2016.

PREVALENCE OF MYD88 L265P MUTATION IN HISTOLOGICALLY PROVEN, DIFFUSE LARGE B-CELL VITREORETINAL LYMPHOMA

Myeloid differentiation primary response gene 88 (MYD88) is a universal adaptor protein in the innate immune system. When associated with a proline for leucine substitution mutation at position 265 (L265P), the protein becomes constitutively activated, amplifying the intracellular pro-inflammatory signal. Recently, we reported two cases of vitreoretinal lymphoma (VRL) that were positive for the mutation. The purpose of this study was to determine prevalence of the MYD88 L265P mutation in a larger series of VRL. Retrospective chart review of 25 patients with histologically confirmed VRL evaluated at Mayo Clinic, Rochester, between January 2000 and March 2015. Paraffin-embedded blocks from the vitreous were submitted for polymerase chain reaction testing of the L265P mutation. The mutation was positive in 82.4% of all VRL cases and 86.7% of primary VRL cases. The minimum necessary DNA concentration needed for the polymerase chain reaction assay was 4.93 ng/mL. MYD88 gene analysis is a helpful ancillary tool for diagnosing VRL. It often requires fewer cells than flow cytometry or cytology and may be especially useful in early cases where a sufficient number of cells may not be available.

In Vitro Selection of Sethoxydim‐Resistant Creeping Bentgrass

Creeping bentgrass (Agrostis stolonifera L.) is a fine‐textured, cold‐hardy turfgrass used by the golf industry in the transition zone and farther north. Grassy weeds are a recurrent problem for seed producers and golf course managers. Herbicide‐resistant creeping bentgrass would provide the seed producer and golf course manager with an additional tool to control grassy weeds. In the present study, in vitro selection was used to obtain mutants of creeping bentgrass via somaclonal variation that were resistant to the acetyl coenzyme A carboxylase (ACCase) inhibitor, sethoxydim {2‐[1‐(ethoxyimino] butyl)‐5‐[2‐(ethylthio)propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one}. Selection was imposed on creeping bentgrass calli (total of 13,725) by growing them on induction medium containing 10 µM sethoxydim. Four independent sethoxydim‐resistant calli were identified and subsequently sequenced to confirm the presence of an A to C mutation in the first position of the 1781 amino acid codon causing an isoleucine to leucine substitution. Whole plant dose response experiments showed the sethoxydim‐resistant event, SR1, was resistant to sethoxydim at rates of >3200 g a.i. ha–1. SR1 also showed cross resistance to the ACCase‐inhibitor herbicide, fenoxaprop at rates of > 800 g a.i. ha–1.

Distinct structural changes in wild-type and amyloidogenic chicken cystatin caused by disruption of C95–C115 disulfide bond

Human cystatin C (HCC) amyloid angiopathy (HCCAA) is characterized by tissue deposition of amyloid fibrils in blood vessels, which can lead to recurrent hemorrhagic stroke. Wild-type HCC forms part of the amyloid deposits in brain arteries of elderly people with amyloid angiopathy. A point mutation causing a glutamine to a leucine substitution at residue 68 in the HCC polypeptide chain greatly increases the amyloidogenic propensity of HCC and causes a more severe cerebral hemorrhage and premature death in young adults. In this study, we used molecular dynamics simulations to assess the importance of disulfide bridge formation upon the stability of chicken cystatin and how this may influence the propensity for amyloid formation. We found that disulfide bridge formation between Cys95 and Cys115 in human cystatin played a critical role in overall protein stability. Importantly, Cys95–Cys115 influenced cystatin structure in regions of the protein that play key roles in the protein-folding transitions that occur, which enable amyloid fibril formation. We hypothesized that correct disulfide bridge formation is a critical step in stabilizing cystatin toward its native conformation. Disrupting Cys95–Cys115 disulfide bridge formation within cystatin appears to significantly enhance the amyloidogenic properties of this protein. In addition, by combining in silico studies with our previous experimental results on Eps1, a molecular chaperone of the PDI family, we proposed that age-related HCCAA, may possess a different pathogenic mechanism compared with its amyloidogenic counterpart, the early onset amyloidogenic cystatin-related CAA.

A stromal interaction molecule 1 variant up-regulates matrix metalloproteinase-2 expression by strengthening nucleoplasmic Ca2+ signaling

Very recent studies hold promise to reveal the role of stromal interaction molecule 1 (STIM1) in non-store-operated Ca2+ entry. Here we showed that in contrast to cytoplasmic membrane redistribution as previously noted, human umbilical vein endothelial STIM1 with a T-to-C nucleotide transition resulting in an amino acid substitution of leucine by proline in the signal peptide sequence translocated to perinuclear membrane upon intracellular Ca2+ depletion, amplified nucleoplasmic Ca2+ signaling through ryanodine receptor-dependent pathway, and enhanced the subsequent cAMP responsive element binding protein activity, matrix metalloproteinase-2 (MMP-2) gene expression, and endothelial tube forming. The abundance of mutated STIM1 and the MMP-2 expression were higher in native human umbilical vein endothelial cells of patients with gestational hypertension than controls and were significantly correlated with blood pressure. These findings broaden our understanding about structure–function bias of STIM1 and offer unique insights into its application in nucleoplasmic Ca2+, MMP-2 expression, endothelial dysfunction, and pathophysiological mechanism(s) of gestational hypertension.

Enhancement of Polymerase Activity of the Large Fragment in DNA Polymerase I from Geobacillus stearothermophilus by Site-Directed Mutagenesis at the Active Site.

The large fragment of DNA polymerase I from Geobacillus stearothermophilus GIM1.543 (Bst DNA polymerase) with 5′-3′ DNA polymerase activity while in absence of 5′-3′ exonuclease activity possesses high thermal stability and polymerase activity. Bst DNA polymerase was employed in isothermal multiple self-matching initiated amplification (IMSA) which amplified the interest sequence with high selectivity and was widely applied in the rapid detection of human epidemic diseases. However, the detailed information of commercial Bst DNA polymerase is unpublished and well protected by patents, which makes the high price of commercial kits. In this study, wild-type Bst DNA polymerase (WT) and substitution mutations for improving the efficiency of DNA polymerization were expressed and purified in E. coli. Site-directed substitutions of four conserved residues (Gly310, Arg412, Lys416, and Asp540) in the activity site of Bst DNA polymerase influenced efficiency of polymerizing dNTPs. The substitution of residue Gly310 by alanine or leucine and residue Asp540 by glutamic acid increased the efficiency of polymerase activity. All mutants with higher polymerizing efficiency were employed to complete the rapid detection of EV71-associated hand, foot, and mouth disease (HFMD) by IMSA approach with relatively shorter period which is suitable for the primary diagnostics setting in rural and underdeveloped areas.

Identification of a novel inherited ALK variant M1199L in the WNT type of medulloblastoma.

Rearrangements involving the ALK gene were identified in a variety of cancers, including paediatric tumour neuroblastoma where presence of ALK expression is also associated with adverse prognosis. Microarrays data indicate that ALK is expressed in another paediatric tumour - medulloblastoma. Therefore, we investigated if the ALK gene is mutated in medulloblastoma and performed simultaneously the molecular profiling of tumours. Tumours from sixty-four medulloblastoma patients were studied for detection of ALK alterations in exons 23 and 25 using Sanger method. The molecular subtypes of tumours were identified by detection of mutations in the CTNNB1 gene, monosomy 6 and by immunohistochemistry using a panel of representative antibodies. Among three ALK variants detected two resulted in intron variants (rs3738867, rs113866835) and the third one was a novel heterozygous variant c.3595A>T in exon 23 identified in the WNT type of tumour. It resulted in methionine to leucine substitution at codon position 1199 (M1199L) of the kinase domain of ALK protein. Results of analysis using three in silico algorithms confirmed the pathogenicity of this single nucleotide variation. The same gene alteration was detected in both patient and maternal peripheral blood leukocytes indicating an inherited type of the detected variant. Presence of ALK expression in tumour tissue was confirmed by immunohistochemistry. The tumour was diagnosed as classic medulloblastoma, however with visible areas of focal anaplastic features. The patient has been disease free for 6 years since diagnosis. This is the first evidence of an inherited ALK variant in the WNT type of medulloblastoma, what altogether with presence of ALK expression may point towards involvement of the ALK gene in this type of tumours.

Deciphering the Dynamics of Non-Covalent Interactions Affecting Thermal Stability of a Protein: Molecular Dynamics Study on Point Mutant of Thermus thermophilus Isopropylmalate Dehydrogenase

Thermus thermophilius isopropylmalate dehydrogenase catalyzes oxidative decarboxylation and dehydrogenation of isopropylmalate. Substitution of leucine to alanine at position 172 enhances the thermal stability among the known point mutants. Exploring the dynamic properties of non-covalent interactions such as saltbridges, hydrogen bonds and hydrophobic interactions to explain thermal stability of a protein is interesting in its own right. In this study dynamic changes in the non-covalent interactions are studied to decipher the deterministic features of thermal stability of a protein considering a case study of a point mutant in Thermus thermophilus isopropylmalate dehydrogenase. A total of four molecular dynamic simulations of 0.2 μs were carried out on wild type and mutant’s functional dimers at 300 K and 337 K. Higher thermal stability of the mutant as compared to wild type is revealed by root mean square deviation, root mean square fluctuations and Cα-Cα distance with an increase in temperature from 300 K to 337 K. Most of the regions of wild type fluctuate higher than the corresponding regions of mutant with an increase in temperature. Cα-Cα distance analysis suggests that long distance networks are significantly affected in wild type as compared to the mutant. Short lived contacts are higher in wild type, while long lived contacts are lost at 337 K. The mutant forms less hydrogen bonds with water as compared to wild type at 337 K. In contrast to wild type, the mutant shows significant increase in unique saltbridges, hydrogen bonds and hydrophobic contacts at 337 K. The current study indicates that there is a strong inter-dependence of thermal stability on the way in which non-covalent interactions reorganize, and it is rewarding to explore this connection in single mutant studies.

Somatic MED12 mutations in prostate cancer and uterine leiomyomas promote tumorigenesis through distinct mechanisms

Mediator is a multiprotein interface between eukaryotic gene-specific transcription factors and RNA polymerase II. Mutations in exon 2 of the gene encoding MED12, a key subunit of the regulatory kinase module in Mediator, are extremely frequent in uterine leiomyomas, breast fibroadenomas, and phyllodes tumors. These mutations disrupt kinase module interactions and lead to diminished Mediator-associated kinase activity. MED12 mutations in exon 26, resulting in a substitution of leucine 1224 to phenylalanine (L1224F), have been recurrently observed in prostate cancer. To elucidate the molecular mechanisms leading to tumorigenesis in prostate cancer, we analyzed global interaction profiles of wild-type and L1224F mutant MED12 with quantitative affinity purification-mass spectrometry (AP-MS). Immunoprecipitation and kinase activity assay were used to further assess the interactions between Mediator complex subunits and kinase activity. The presence of L1224F mutation was analyzed in altogether 877 samples representing prostate hyperplasia, prostate cancer, and various tumor types in which somatic MED12 mutations have previously been observed. In contrast to N-terminal MED12 mutations observed in uterine leiomyomas, the L1224F mutation compromises neither the interaction of MED12 with kinase module subunits Cyclin C and CDK8/19 nor Mediator-associated CDK activity. Instead, the L1224F mutation was shown to affect interactions between MED12 and other Mediator components (MED1, MED13, MED13L, MED14, MED15, MED17, and MED24). Mutation screening revealed one mutation in a Finnish (Caucasian) prostate cancer patient, whereas no mutations in any other tumor type were observed. Specific somatic MED12 mutations in prostate cancer and uterine leiomyomas accumulate in two separate regions of the gene and promote tumorigenesis through clearly distinct mechanisms.

Point mutation of cytochrome P450 2A6 (a polymorphic variant CYP2A6.25) confers new substrate specificity towards flavonoids.

CYP2A6 is a major hepatic member of the cytochrome P450 family in humans. Much variation in CYP2A6 levels and activity can be attributed to genetic polymorphisms of this gene. CYP2A6*25 comprises an amino acid substitution, F118L. To clarify the effect of the leucine substitution at position 118 in CYP2A6.25, this variant, wild type CYP2A6 and three additional variants consisting of artificial mutations at the substrate binding site (position 481) suggested by earlier reports using random mutagenesis studies [CYP2A6.1, CYP2A6.25, CYP2A6.1(F118A), CYP2A6.1(A481G) and CYP2A6.25(A481G)], were co-expressed with NADPH-cytochrome P450 reductase in E. coli. The hydroxylase activity of these variants toward 7-ethoxycoumarin, coumarin, flavone, α-naphthoflavone, flavanone and hydroxyflavanone were examined. All the mutants had lower activities for coumarin 7-hydroxylation than the wild type. All the mutants showed higher activities for flavone and α-naphthoflavone compared with CYP2A6.1. CYP2A6.1 had the highest flavanone 2'-hydroxylase activity, whereas CYP2A6.25 had the highest 6- and 4'-hydroxylase activities. CYP2A6.1(F118A), CYP2A6.1(A481G) and CYP2A6.25(A481G) had higher flavanone 3'-hydroxylase activities than CYP2A6.1 and CYP2A6.25. Furthermore, 4'-hydroxyflavanone was metabolized by CYP2A6.25. These results indicate that the CYP2A6.25 mutation confers new substrate specificity towards flavonoids.

Abstract 4961: Functional analysis of prostate cancer-specific MED12 mutation

Abstract Mediator is a highly conserved protein complex regulating RNA polymerase II-dependent transcription. It also mediates transcriptional signals from several gene-specific transcription factors. In higher eukaryotes the core Mediator comprises 26 subunits organized into three distinct modules; head, middle, and tail. Separate kinase module regulating the activity of the Mediator is formed by MED12, MED13, Cyclin C, and CDK8/19. Mediator complex subunit 12 (MED12) gene on Xq13.1 encodes MED12 protein which links the kinase module to the Mediator core and is required for Cyclin C-dependent CDK8 activity. Somatic mutations in 5′-terminus of MED12 are highly frequent in uterine leiomyomas and in breast fibroadenomas. Similar mutations occur recurrently, although with lower frequencies, also in uterine leiomyosarcomas and in chronic lymphocytic leukemia. All the observed mutations have been missense mutations or in-frame insertions and deletions in exons 1 and 2. Functional analyses have indicated that mutations in both exon 1 and exon 2 lead to dissociation of Cyclin C-CDK8/19 from the core Mediator, loss of Mediator-associated CDK kinase activity, and similar global gene expression profiles. Following the initial observation of MED12 mutations in uterine leiomyomas, exome sequencing study by Barbieri and co-workers identified a recurrent MED12 mutation in prostate cancer. Seven mutations were observed in total and strikingly five of these affected the same codon in exon 26 resulting in substitution of leucine 1224 with phenylalanine. The same L1224F mutation has been observed in prostate cancer in sequencing efforts by The Cancer Genome Atlas. The aim of this study was to elucidate the molecular mechanisms by which the mutation causes tumorigenesis in prostate cancer. To identify the possible effects on protein-protein interactions, we generated stable and inducible HEK293 Flp-In cell lines expressing MED12 wild type and L1224F mutant protein and performed affinity purification followed by liquid chromatography-mass spectrometry. Interactions with other subunits of the Mediator core and the kinase module were further analyzed with immunoprecipitations accompanied with Western blotting. In addition, Mediator-associated CDK kinase activity of the kinase modules with respective protein constructs were measured. Based on these analyzes, L1224F mutation does not interfere the interaction between MED12 and Cyclin C-CDK8/19, and thus does not lead to reduced Mediator-associated CDK kinase activity. Significant decrease was, however, observed in the binding of L1224F mutant versus wild type protein with several other Mediator subunits. These results indicate that prostate cancer-specific MED12 mutation is promoting tumorigenesis through clearly distinct mechanisms than the ones seen in myomagenesis. Citation Format: Kati Kämpjärvi, Nam Hee Kim, Min Ju Park, Mikko Turunen, Netta Mäkinen, Tuomas Heikkinen, Salla Keskitalo, Markku Varjosalo, Thomas G. Boyer, Pia Vahteristo. Functional analysis of prostate cancer-specific MED12 mutation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4961. doi:10.1158/1538-7445.AM2015-4961

Utilizing Chemical Genomics to Identify Cytochrome b as a Novel Drug Target for Chagas Disease.

Unbiased phenotypic screens enable identification of small molecules that inhibit pathogen growth by unanticipated mechanisms. These small molecules can be used as starting points for drug discovery programs that target such mechanisms. A major challenge of the approach is the identification of the cellular targets. Here we report GNF7686, a small molecule inhibitor of Trypanosoma cruzi, the causative agent of Chagas disease, and identification of cytochrome b as its target. Following discovery of GNF7686 in a parasite growth inhibition high throughput screen, we were able to evolve a GNF7686-resistant culture of T. cruzi epimastigotes. Clones from this culture bore a mutation coding for a substitution of leucine by phenylalanine at amino acid position 197 in cytochrome b. Cytochrome b is a component of complex III (cytochrome bc1) in the mitochondrial electron transport chain and catalyzes the transfer of electrons from ubiquinol to cytochrome c by a mechanism that utilizes two distinct catalytic sites, QN and QP. The L197F mutation is located in the QN site and confers resistance to GNF7686 in both parasite cell growth and biochemical cytochrome b assays. Additionally, the mutant cytochrome b confers resistance to antimycin A, another QN site inhibitor, but not to strobilurin or myxothiazol, which target the QP site. GNF7686 represents a promising starting point for Chagas disease drug discovery as it potently inhibits growth of intracellular T. cruzi amastigotes with a half maximal effective concentration (EC50) of 0.15 µM, and is highly specific for T. cruzi cytochrome b. No effect on the mammalian respiratory chain or mammalian cell proliferation was observed with up to 25 µM of GNF7686. Our approach, which combines T. cruzi chemical genetics with biochemical target validation, can be broadly applied to the discovery of additional novel drug targets and drug leads for Chagas disease.

Different Roles of N-Terminal and C-Terminal Domains in Calmodulin for Activation of Bacillus anthracis Edema Factor.

Bacillus anthracis adenylyl cyclase toxin edema factor (EF) is one component of the anthrax toxin and is essential for establishing anthrax disease. EF activation by the eukaryotic Ca2+-sensor calmodulin (CaM) leads to massive cAMP production resulting in edema. cAMP also inhibits the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, thus reducing production of reactive oxygen species (ROS) used for host defense in activated neutrophils and thereby facilitating bacterial growth. Methionine (Met) residues in CaM, important for interactions between CaM and its binding partners, can be oxidized by ROS. We investigated the impact of site-specific oxidation of Met in CaM on EF activation using thirteen CaM-mutants (CaM-mut) with Met to leucine (Leu) substitutions. EF activation shows high resistance to oxidative modifications in CaM. An intact structure in the C-terminal region of oxidized CaM is sufficient for major EF activation despite altered secondary structure in the N-terminal region associated with Met oxidation. The secondary structures of CaM-mut were determined and described in previous studies from our group. Thus, excess cAMP production and the associated impairment of host defence may be afforded even under oxidative conditions in activated neutrophils.

Transmission Properties of Human PrP 102L Prions Challenge the Relevance of Mouse Models of GSS.

Inherited prion disease (IPD) is caused by autosomal-dominant pathogenic mutations in the human prion protein (PrP) gene (PRNP). A proline to leucine substitution at PrP residue 102 (P102L) is classically associated with Gerstmann-Sträussler-Scheinker (GSS) disease but shows marked clinical and neuropathological variability within kindreds that may be caused by variable propagation of distinct prion strains generated from either PrP 102L or wild type PrP. To-date the transmission properties of prions propagated in P102L patients remain ill-defined. Multiple mouse models of GSS have focused on mutating the corresponding residue of murine PrP (P101L), however murine PrP 101L, a novel PrP primary structure, may not have the repertoire of pathogenic prion conformations necessary to accurately model the human disease. Here we describe the transmission properties of prions generated in human PrP 102L expressing transgenic mice that were generated after primary challenge with ex vivo human GSS P102L or classical CJD prions. We show that distinct strains of prions were generated in these mice dependent upon source of the inoculum (either GSS P102L or CJD brain) and have designated these GSS-102L and CJD-102L prions, respectively. GSS-102L prions have transmission properties distinct from all prion strains seen in sporadic and acquired human prion disease. Significantly, GSS-102L prions appear incapable of transmitting disease to conventional mice expressing wild type mouse PrP, which contrasts strikingly with the reported transmission properties of prions generated in GSS P102L-challenged mice expressing mouse PrP 101L. We conclude that future transgenic modeling of IPDs should focus exclusively on expression of mutant human PrP, as other approaches may generate novel experimental prion strains that are unrelated to human disease.

Two novel mutations of CLCN7 gene in Chinese families with autosomal dominant osteopetrosis (type II)

Autosomal dominant osteopetrosis type II (ADO-II) is a heritable bone disorder characterized by osteosclerosis, predominantly involving the spine (vertebral end-plate thickening, or rugger-jersey spine), the pelvis ("bone-within-bone" structures) and the skull base. Chloride channel 7 (CLCN7) has been reported to be the causative gene. In this study, we aimed to identify the pathogenic mutation in four Chinese families with ADO-II. All 25 exons of the CLCN7 gene, including the exon-intron boundaries, were amplified and sequenced directly in four probands from the Chinese families with ADO-II. The mutation site was then identified in other family members and 250 healthy controls. In family 1, a known missense mutation c.296A>G in exon 4 of CLCN7 was identified in the proband, resulting in a tyrosine (UAU) to cysteine (UGU) substitution at p.99 (Y99C); the mutation was also identified in his affected father. In family 2, a novel missense mutation c.865G>C in exon 10 was identified in the proband, resulting in a valine (GUC) to leucine (CUC) substitution at p.289 (V289L); the mutation was also identified in her healthy mother and sister. In family 3, a novel missense mutation c.1625C>T in exon 17 of CLCN7 was identified in the proband, resulting in an alanine (GCG) to valine (GUG) substitution at p.542 (A542V); the mutation was also identified in her father. In family 4, a hot spot, R767W (c.2299C>T, CGG>TGG), in exon 24 was found in the proband which once again proved the susceptibility of the site or the similar genetic background in different races. Moreover, two novel mutations, V289L and A542V, occurred at a highly conserved position, found by a comparison of the protein sequences from eight vertebrates, and were predicted to have a pathogenic effect by PolyPhen-2 software, which showed "probably damaging" with a score of approximately 1. These mutation sites were not identified in 250 healthy controls. Our present findings suggest that the novel missense mutations V289L and A542V in the CLCN7 gene were responsible for ADO-II in the two Chinese families.

Molecular phenotype of tissue-nonspecific alkaline phosphatase with a proline (108) to leucine substitution associated with dominant odontohypophosphatasia.

Hypophosphatasia (HPP) is a genetic disease characterized by defective calcification of hard tissues such as bone and teeth accompanying deficiency of serum alkaline phosphatase (ALP) activity. Its development results from various mutations in the ALPL gene encoding tissue-nonspecific ALP (TNSALP). HPP is known to be transmitted in an autosomal recessive or autosomal dominant manner. A point mutation (c.323C>T) in the ALPL gene leading to a proline to leucine substitution at position 108 of TNSALP was first reported in a patient diagnosed with odonto-HPP (M Herasse et al., J Med Genet 2003;40:605-609), although the effects of this mutation on the TNSALP molecule have not been elucidated. To understand the molecular basis of this dominantly transmitted HPP, we first characterized TNSALP (P108L) by expressing it in COS-1 cells transiently. In contrast to wild-type TNSALP (WT), TNSALP (P108L) showed virtually no ALP activity. When coexpressed with TNSALP (WT), TNSALP (P108L) significantly inhibited the enzyme activity of TNSALP (WT), confirming that this mutant TNSALP exerts a dominant negative effect on TNSALP (WT). Using immunofluorescence and digestion with phosphatidylinositol-specific phospholipase C, we demonstrated that TNSALP (P108L) was anchored to the cell surface via glycosylphosphatidylinositol-like TNSALP (WT) in a Tet-On CHO cell expression system. Consistent with this, TNSALP (P108L) acquired endo-β-N-acetylglucosaminidase H resistance and sialic acids, as evidenced by glycosidase treatments. Importantly, TNSALP (WT) largely formed a functional dimeric structure, while TNSALP (P108L) was found to be present as a monomer in the cell. This indicates that the molecular structure of TNSALP is affected by a missense mutation at position 108, which is in contact with the active site, such that it no longer assembles into the functional dimeric form. Collectively, these results may explain why TNSALP (P108L) loses its ALP activity, even though it is able to gain access to the cell surface.

Hb Dartmouth (HBA2: c.200T>C): An α2-Globin Gene Associated with Hb H Disease in One Homozygous Patient

Hb H (β4) disease is caused by deletion or inactivation of three out of four α-globin genes. A high incidence of Hb H disease has been reported all over the world. There is a wide spectrum of phenotypic presentations, from clinically asymptomatic to having significant hepatosplenomegaly and requiring occasional or even regular blood transfusions, even more severe anemia, Hb Bart’s (γ4) hydrops fetalis syndrome that can cause death in the affected fetuses late in gestation. We here present a case who was diagnosed with Hb H disease that represents a new genotype for this hereditary disorder. Hb Dartmouth is a variant caused by a missense mutation at codon 66 of the α2-globin gene (HBA2: c.200T>C), resulting in the substitution of leucine by proline. We here emphasize the importance of this point mutation involving Hb H disease and also the necessity for prenatal diagnosis (PND) for those who carry this point mutation in the heterozygous state.