Biosynthesis Of Glycoconjugates Research Articles

Mapping the architecture of the initiating phosphoglycosyl transferase from S. enterica O-antigen biosynthesis in a liponanoparticle

Bacterial cell surface glycoconjugates are critical for cell survival and for interactions between bacteria and their hosts. Consequently, the pathways responsible for their biosynthesis have untapped potential as therapeutic targets. The localization of many glycoconjugate biosynthesis enzymes to the membrane represents a significant challenge for expressing, purifying, and characterizing these enzymes. Here, we leverage cutting-edge detergent-free methods to stabilize, purify, and structurally characterize WbaP, a phosphoglycosyl transferase (PGT) from the Salmonella enterica (LT2) O-antigen biosynthesis. From a functional perspective, these studies establish WbaP as a homodimer, reveal the structural elements responsible for dimerization, shed light on the regulatory role of a domain of unknown function embedded within WbaP, and identify conserved structural motifs between PGTs and functionally unrelated UDP-sugar dehydratases. From a technological perspective, the strategy developed here is generalizable and provides a toolkit for studying other classes of small membrane proteins embedded in liponanoparticles beyond PGTs.

Uridine Bisphosphonates Differentiate Phosphoglycosyl Transferase Superfamilies.

Complex bacterial glycoconjugates drive interactions between pathogens, symbionts, and their human hosts. Glycoconjugate biosynthesis is initiated at the membrane interface by phosphoglycosyl transferases (PGTs), which catalyze the transfer of a phosphosugar from a soluble uridine diphosphosugar (UDP-sugar) substrate to a membrane-bound polyprenol-phosphate (Pren-P). The two distinct superfamilies of PGT enzymes (polytopic and monotopic) show striking differences in their structure and mechanism. We designed and synthesized a series of uridine bisphosphonates (UBPs), wherein the diphosphate of the UDP and UDP-sugar is replaced by a substituted methylene bisphosphonate (CXY-BPs; X/Y = F/F, Cl/Cl, (S)-H/F, (R)-H/F, H/H, CH3/CH3). UBPs and UBPs incorporating an N-acetylglucosamine (GlcNAc) substituent at the β-phosphonate were evaluated as inhibitors of a polytopic PGT (WecA from Thermotoga maritima) and a monotopic PGT (PglC from Campylobacter jejuni). Although CHF-BP most closely mimics diphosphate with respect to its acid/base properties, the less basic CF2-BP conjugate more strongly inhibited PglC, whereas the more basic CH2-BP analogue was the strongest inhibitor of WecA. These surprising differences indicate different modes of ligand binding for the different PGT superfamilies, implicating a modified P-O- interaction with the structural Mg2+. For the monoPGT enzyme, the two diastereomeric CHF-BP conjugates, which feature a chiral center at the Pα-CHF-Pβ carbon, also exhibited strikingly different binding affinities and the inclusion of GlcNAc with the native α-anomer configuration significantly improved binding affinity. UBP-sugars are thus revealed as informative new mechanistic probes of PGTs that may aid development of novel antibiotic agents for the exclusively prokaryotic monoPGT superfamily.

Specificity determinants revealed by the structure of glycosyltransferase Campylobacter concisus PglA.

In selected Campylobacter species, the biosynthesis of N-linked glycoconjugates via the pgl pathway is essential for pathogenicity and survival. However, most of the membrane-associated GT-B fold glycosyltransferases responsible for diversifying glycans in this pathway have not been structurally characterized which hinders the understanding of the structural factors that govern substrate specificity and prediction of resulting glycan composition. Herein, we report the 1.8 Å resolution structure of Campylobacter concisus PglA, the glycosyltransferase responsible for the transfer of N-acetylgalatosamine (GalNAc) from uridine 5'-diphospho-N-acetylgalactosamine (UDP-GalNAc) to undecaprenyl-diphospho-N,N'-diacetylbacillosamine (UndPP-diNAcBac) in complex with the sugar donor GalNAc. This study identifies distinguishing characteristics that set PglA apart within the GT4 enzyme family. Computational docking of the structure in the membrane in comparison to homologs points to differences in interactions with the membrane-embedded acceptor and the structural analysis of the complex together with bioinformatics and site-directed mutagenesis identifies donor sugar binding motifs. Notably, E113, conserved solely among PglA enzymes, forms a hydrogen bond with the GalNAc C6″-OH. Mutagenesis of E113 reveals activity consistent with this role in substrate binding, rather than stabilization of the oxocarbenium ion transition state, a function sometimes ascribed to the corresponding residue in GT4 homologs. The bioinformatic analyses reveal a substrate-specificity motif, showing that Pro281 in a substrate binding loop of PglA directs configurational preference for GalNAc over GlcNAc. This proline is replaced by a conformationally flexible glycine, even in distant homologs, which favor substrates with the same stereochemistry at C4, such as glucose. The signature loop is conserved across all Campylobacter PglA enzymes, emphasizing its importance in substrate specificity.

Bittersweet Sugars: How Unusual Glycan Structures May Connect Epithelial-to-Mesenchymal Transition and Multidrug Resistance in Cancer.

Cancer cells are characterized by metabolic reprogramming, which enables their survival in of-ten inhospitable conditions. A very well-documented example that has gained attraction in re-cent years and is already considered a hallmark of transformed cells is the reprogramming of carbohydrate metabolism. Such a feature, in association with the differential expression of en-zymes involved in the biosynthesis of glycoconjugates, generically known as glycosyltransfer-ases, contributes to the expression of structurally atypical glycans when compared to those ex-pressed in healthy tissues. The latest studies have demonstrated that glycophenotypic alterations are capable of modulating multifactorial events essential for the development and/or progres-sion of the disease. Herein, we will address the importance of glycobiology in modern medi-cine, focusing on the ability of unusual/truncated O-linked glycans to modulate two complex and essential phenomena for cancer progression: the acquisition of the multidrug resistance (MDR) phenotype and the activation of molecular pathways associated with the epithelial-mesenchymal transition (EMT) process, an event deeply linked with cancer metastasis.

Co-conserved sequence motifs are predictive of substrate specificity in a family of monotopic phosphoglycosyl transferases.

Monotopic phosphoglycosyl transferases (monoPGTs) are an expansive superfamily of enzymes that catalyze the first membrane-committed step in the biosynthesis of bacterial glycoconjugates. MonoPGTs show a strong preference for their cognate nucleotide diphospho-sugar (NDP-sugar) substrates. However, despite extensive characterization of the monoPGT superfamily through previous development of a sequence similarity network comprising >38,000 nonredundant sequences, the connection between monoPGT sequence and NDP-sugar substrate specificity has remained elusive. In this work, we structurally characterize the C-terminus of a prototypic monoPGT for the first time and show that 19 C-terminal residues play a significant structural role in a subset of monoPGTs. This new structural information facilitated the identification of co-conserved sequence "fingerprints" that predict NDP-sugar substrate specificity for this subset of monoPGTs. A Hidden Markov model was generated that correctly assigned the substrate of previously unannotated monoPGTs. Together, these structural, sequence, and biochemical analyses have delivered new insight into the determinants guiding substrate specificity of monoPGTs and have provided a strategy for assigning the NDP-sugar substrate of a subset of enzymes in the superfamily that use UDP-di-N-acetyl bacillosamine. Moving forward, this approach may be applied to identify additional sequence motifs that serve as fingerprints for monoPGTs of differing UDP-sugar substrate specificity.

A generalizable protocol for expression and purification of membrane-bound bacterial phosphoglycosyl transferases in liponanoparticles

Phosphoglycosyl transferases (PGTs) are among the first membrane-bound enzymes involved in the biosynthesis of bacterial glycoconjugates. Robust expression and purification protocols for an abundant subfamily of PGTs remains lacking. Recent advancements in detergent-free methods for membrane protein solubilization open the door for purification of difficult membrane proteins directly from cell membranes into native-like liponanoparticles. By leveraging autoinduction, in vivo SUMO tag cleavage, styrene maleic acid co-polymer liponanoparticles (SMALPs), and Strep-Tag purification, we have established a robust workflow for expression and purification of previously unobtainable PGTs. The material generated from this workflow is extremely pure and can be directly visualized by Cryogenic Electron Microscopy (CryoEM). The methods presented here promise to be generalizable to additional membrane proteins recombinantly expressed in E. coli and should be of interest to the greater membrane proteomics community.

Identification of lthB, a Gene Encoding a Putative Glycosyltransferase Family 8 Protein Required for Leptothrix Sheath Formation.

The bacterium Leptothrix cholodnii generates cell chains encased in sheaths that are composed of woven nanofibrils. The nanofibrils are mainly composed of glycoconjugate repeats, and several glycosyltransferases (GTs) are required for its biosynthesis. However, only one GT (LthA) has been identified to date. In this study, we screened spontaneous variants of L. cholodnii SP6 to find those that form smooth colonies, which is one of the characteristics of sheathless variants. Genomic DNA sequencing of an isolated variant revealed an insertion in the locus Lcho_0972, which encodes a putative GT family 8 protein. We thus designated this protein LthB and characterized it using deletion mutants and antibodies. LthB localized adjacent to the cell envelope. ΔlthB cell chains were nanofibril free and thus sheathless, indicating that LthB is involved in nanofibril biosynthesis. Unlike the ΔlthA mutant and the wild-type strain, which often generate planktonic cells, most ΔlthB organisms presented as long cell chains under static conditions, resulting in deficient pellicle formation, which requires motile planktonic cells. These results imply that sheaths are not required for elongation of cell chains. Finally, calcium depletion, which induces cell chain breakage due to sheath loss, abrogated the expression of LthA, but not LthB, suggesting that these GTs cooperatively participate in glycoconjugate biosynthesis under different signaling controls. IMPORTANCE In recent years, the regulation of cell chain elongation of filamentous bacteria via extracellular signals has attracted attention as a potential strategy to prevent clogging of water distribution systems and filamentous bulking of activated sludge in industrial settings. However, a fundamental understanding of the ecology of filamentous bacteria remains elusive. Since sheath formation is associated with cell chain elongation in most of these bacteria, the molecular mechanisms underlying nanofibril sheath formation, including the intracellular signaling cascade in response to extracellular stimuli, must be elucidated. Here, we isolated a sheathless variant of L. cholodnii SP6 and thus identified a novel glycosyltransferase, LthB. Although mutants with deletions of lthA, encoding another GT, and lthB were both defective for nanofibril formation, they exhibited different phenotypes of cell chain elongation and pellicle formation. Moreover, LthA expression, but not LthB expression, was influenced by extracellular calcium, which is known to affect nanofibril formation, indicating the functional diversities of LthA and LthB. Such molecular insights are critical for a better understanding of ecology of filamentous bacteria, which, in turn, can be used to improve strategies to control filamentous bacteria in industrial facilities.

AepG is a glucuronosyltransferase involved in acidic exopolysaccharide synthesis and contributes to environmental adaptation of Haloarcula hispanica

The attachment of a sugar to a hydrophobic lipid carrier is the first step in the biosynthesis of many glycoconjugates. In the halophilic archaeon Haloarcula hispanica, HAH_1206, renamed AepG, is a predicted glycosyltransferase belonging to the CAZy Group 2 family that shares a conserved amino acid sequence with dolichol phosphate mannose synthases. In this study, the function of AepG was investigated by genetic and biochemical approaches. We found that aepG deletion led to the disappearance of dolichol phosphate-glucuronic acid. Our biochemical assays revealed that recombinant cellulose-binding, domain-tagged AepG could catalyze the formation of dolichol phosphate-glucuronic acid in time- and dose-dependent manners. Based on the invivo and invitro analyses, AepG was confirmed to be a dolichol phosphate glucuronosyltransferase involved in the synthesis of the acidic exopolysaccharide produced by H.hispanica. Furthermore, lack of aepG resulted in hindered growth and cell aggregation in high salt medium, indicating that AepG is vital for the adaptation of H.hispanica to a high salt environment. In conclusion, AepG is the first dolichol phosphate glucuronosyltransferase identified in any of the three domains of life and, moreover, offers a starting point for further investigation into the diverse pathways used for extracellular polysaccharide biosynthesis in archaea.

Nucleotide sugar transporter SLC35A2 is involved in promoting hepatocellular carcinoma metastasis by regulating cellular glycosylation.

Recently, aberrant glycosylation has been recognized to be relate to malignant behaviors of cancer and outcomes of patients with various cancers. SLC35A2 plays an indispensable role on glycosylation as a nucleotide sugar transporter. However, effects of SLC35A2 on malignant behaviors of cancer cells and alteration of cancer cells surface glycosylation profiles are still not fully understood, particularly in hepatocellular carcinoma (HCC). Hence, from a glycosylation perspective, we investigated the effects of SLC35A2 on metastatic behaviors of HCC cells. SLC35A2 expression in clinical samples and HCC cells was examined by immunohistochemical staining or Western blot/quantitative PCR and was regulated by RNA interference or vectors-mediated transfection. Effects of SLC35A2 expression alteration on metastatic behaviors and membrane glycan profile of HCC cells were observed by using respectively invasion, migration, cell adhesion assay, in vivo lung metastatic nude mouse model and lectins microarray. Co-location among proteins in HCC cells was observed by fluorescence microscope and detected by an in vitro co-immunoprecipitation assay. SLC35A2 was upregulated in HCC tissues, and is associated with poor prognosis of HCC patients. SLC35A2 expression alteration significantly affected the invasion, adhesion, metastasis and membrane glycan profile and led to the dysregulated expressions or glycosylation of cell adhesion-related molecules in HCC cells. Mechanistically, the maintenance of SLC35A2 activity is critical for the recruitment of the key galactosyltransferase B4GalT1, which is responsible for complex glycoconjugate and lactose biosynthesis, to Golgi apparatus in HCC cells. SLC35A2 plays important roles in promoting HCC metastasis by regulating cellular glycosylation modification and inducing the cell adhesive ability of HCC cells.

Probing Monotopic Phosphoglycosyl Transferases from Complex Cellular Milieu.

Monotopic phosphoglycosyl transferase enzymes (monoPGTs) initiate the assembly of prokaryotic glycoconjugates essential for bacterial survival and proliferation. MonoPGTs belong to an expansive superfamily with a diverse and richly annotated sequence space; however, the biochemical roles of most monoPGTs in glycoconjugate biosynthesis pathways remain elusive. To better understand these critical enzymes, we have implemented activity-based protein profiling (ABPP) probes as protein-centric, membrane protein compatible tools that lay the groundwork for understanding the activity and regulation of the monoPGT superfamily from a cellular proteome. With straightforward gel-based readouts, we demonstrate robust, covalent labeling at the active site of various representative monoPGTs from cell membrane fractions using 3-phenyl-2H-azirine probes.

Expanding the Substrate Scope of a Bacterial Nucleotidyltransferase via Allosteric Mutations.

Bacterial glycoconjugates, such as cell surface polysaccharides and glycoproteins, play important roles in cellular interactions and survival. Enzymes called nucleotidyltransferases use sugar-1-phosphates and nucleoside triphosphates (NTPs) to produce nucleoside diphosphate sugars (NDP-sugars), which serve as building blocks for most glycoconjugates. Research spanning several decades has shown that some bacterial nucleotidyltransferases have broad substrate tolerance and can be exploited to produce a variety of NDP-sugars in vitro. While these enzymes are known to be allosterically regulated by NDP-sugars and their fragments, much work has focused on the effect of active site mutations alone. Here, we show that rational mutations in the allosteric site of the nucleotidyltransferase RmlA lead to expanded substrate tolerance and improvements in catalytic activity that can be explained by subtle changes in quaternary structure and interactions with ligands. These observations will help inform future studies on the directed biosynthesis of diverse bacterial NDP-sugars and downstream glycoconjugates.

The role of bacterial ATP-binding cassette (ABC) transporters in pathogenesis and virulence: Therapeutic and vaccine potential

The ATP-binding cassette (ABC) transporter superfamily is found in all domains of life, facilitating critical biological processes through the translocation of a wide variety of substrates from, ions to proteins, across cellular membranes in an ATP-coupled process. The role of ABC transporters in eukaryotes has been well established: the facilitation of genetic diseases and multi-drug resistance (MDR) in cancer patients. In contrast, the role of ABC transporters in prokaryotes has been ambiguous due to their diverse functions and the sheer number of organisms in which they reside. This review examines the role of bacterial ABC transporters in pathogenesis and virulence, and their potential for therapeutic and vaccine application. We demonstrate how ABC transporters play a vital role in the virulence and pathogenesis of several pathogenic bacteria through the import of essential molecules, such as metal ions, amino acids, peptides, vitamins and osmoprotectants, as well as, the export of virulent determinants involved in glycoconjugate biosynthesis and Type I secretion. Furthermore, ABC exporters facilitate the persistence of pathogenic bacteria through the export of toxic xenobiotic substances, thus, contributing to the development of antimicrobial resistance. We also show that ABC transporters display considerable potential for therapeutic application through immunisation and resistance reversal. In conclusion, bacterial ABC transporters play an immense role in virulence and pathogenesis and display desirable traits for clinical use, therefore, potentially aiding in the battle against MDR.

Aberrant Protein Glycosylation in Brain Cancers, with Emphasis on Glioblastoma.

Aberrant glycosylation has been associated with several processes of tumorigenesis from cell signaling, migration and invasion, to immune regulation and metastasis formation. The biosynthesis of glycoconjugates is regulated through concerted and finely tuned enzymatic reactions. This includes the levels and activity of glycosyltransferases and glycosidases, nucleotide sugar metabolism, substrate availability, epigenetic condition, and cellular functional state. Glioblastoma (GBM) is the most aggressive brain tumor, frequently occurring in adults with overall survival not surpassing 17months after diagnosis. GBM has been classified by the World Health Organization (WHO) as a grade 4 astrocytoma and stratified into G-CIMP, proneural, classical, and mesenchymal subtypes. Several biomolecular features associated with GBM aggressiveness have been elucidated; however, more studies are needed to elucidate the role of glycosylation in GBM pathology, looking at their potential as cancer targets. Here, we focus on the alteration of genes involved in protein N- and O-linked glycosylation in GBM. Specifically, the mRNA levels of glycogenes were analyzed using astrocytoma-TCGA-RNAseq datasets from public repositories. A total of 68 genes were differentially regulated in the most aggressive, mesenchymal subtype of GBM compared to the proneural and classical subtypes, and the expression of these genes was compared to normal brain tissues. Among them, we focused on 38 genes coding for proteins that belong to: 1) asparagine glycosylation (ALG); 2) glycosyltransferases (B3T, B4T); 3) fucosyltransferase (FUT); 4) acetylgalactosaminyltransferases (GALNT); 5) hexosaminidase (HEX); 6) mannosidase (MAN); 7) acetylglucosaminyltransferase (MGAT); 8) sialidase or neuraminidase (NEU); 9) solute carrier 35 family (SLC); and 10) sialyltransferase (ST). The differential expression of some genes was already reported in several solid tumors; however, several of them were found to be dysregulated in GBM for the first time. These data represent an important starting point to perform further orthogonal and functional validations to pinpoint the role of these glycogenes in GBM as diagnostic and therapeutic targets.

Dynamic tracing of sugar metabolism reveals the mechanisms of action of synthetic sugar analogs.

Synthetic sugar analogs are widely applied in metabolic oligosaccharide engineering (MOE) and as novel drugs to interfere with glycoconjugate biosynthesis. However, mechanistic insights on their exact cellular metabolism over time are mostly lacking. We combined ion-pair ultrahigh performance liquid chromatography–triple quadrupole mass spectrometry mass spectrometry using tributyl- and triethylamine buffers for sensitive analysis of sugar metabolites in cells and organisms and identified low abundant nucleotide sugars, such as UDP-arabinose in human cell lines and CMP-sialic acid (CMP-NeuNAc) in Drosophila. Furthermore, MOE revealed that propargyloxycarbonyl (Poc)-labeled ManNPoc was metabolized to both CMP-NeuNPoc and UDP-GlcNPoc. Finally, time-course analysis of the effect of antitumor compound 3Fax-NeuNAc by incubation of B16-F10 melanoma cells with N-acetyl-D-[UL-13C6]glucosamine revealed full depletion of endogenous ManNAc 6-phosphate and CMP-NeuNAc within 24 h. Thus, dynamic tracing of sugar metabolic pathways provides a general approach to reveal time-dependent insights into the metabolism of synthetic sugars, which is important for the rational design of analogs with optimized effects.

Optimization of the UDP-Xyl biocatalytic synthesis from Crassostrea gigas by orthogonal design method

UDP-Xyl, a nucleotide sugar involved in the biosynthesis of various glycoconjugates, is difficult to obtain and quite expensive. Biocatalysis using a one-pot multi-enzyme cascade is one of the most valuable biotransformation processes widely used in the industry. Herein, two enzymes, UDP-glucose (UDP-Glc) dehydrogenase (CGIUGD) and UDP-Xyl synthase (CGIUXS) from the Pacific oyster Crassostrea gigas, which are coupled together for the biotransformation of UDP-Xyl, were characterized. The optimum pH was determined to be pH 9.0 for CGIUGD and pH 7.5 for CGIUXS. Both enzymes showed the highest activity at 37 °C. Neither enzyme is metal ion-dependent. On this basis, a single factor and orthogonal test were applied to optimize the condition of biotransformation of UDP-Xyl from UDP-Glc. Orthogonal design L9 (33) was conducted to optimize processing variables of enzyme amount, pH, and temperature. The conversion of UDP-Xyl was selected as an analysis indicator. Optimum variables were the ratio of CGIUGD to CGIUXS of 2:5, enzymatic pH of 8.0, and temperature of 37 °C, which is confirmed by three repeated validation experiments. The UDP-Xyl conversion was 69.921% in a 1 mL reaction mixture by optimized condition for 1 h. This is the first report for the biosynthesis of UDP-Xyl from oyster enzymes.

The screening by isoelectric focusing of transferrin for the diagnosis of congenital disorders of glycosylation

Background: Congenital Disorders of Glycosylation (CDG) are a group of inherited metabolic disorders caused by the defect in various steps in the biosynthesis of glycoproteins and other glycoconjugates. Material and methods: 40 patients under clinical suspicions for CDG at the Institute of Mother and Child were examined by isoelectric focusing of transferrin (IEFT) in collaboration with RadboudUMC, Netherlands and U.S.A. The spectrum of clinical presentations of these patients was multisystem damage, predominantly neurological manifestations. Results: Most of the patients (55%) had early neurological manifestations from the birth, such as hypotonia, psychomotor disability, cerebral MRI abnormalities, seizures (25%), cutis laxa (17.5%), total alopecia (2.5%), abnormal fat pads (2.5%), myopia (7.5%), nystagmus (5%), strabismus (2.5%), stroke-like episodes (2.5.%), ataxia (7.5%), abnormal coagulation (10%), hepatomegaly (35%) and liver cirrhosis (2.5%). Serum samples analyzed by IEFT showed the results: 37 normal, 2 questionable and 1 abnormal patterns. Two samples questionable belongs to the patients with Galactosemia and Fructosemia, which give the false-positive results. The last positive sample is performed additionally for glycomics profiling. In some cases, with IEFT negative profile was performed genetic test and were diagnosed other diseases, mimicking CDG, such as: NARP syndrome, late diagnosed PKU, GSD, Manosidoses, Prader-Willi Syndrome and chromosomal aberrations. Conclusions: The CDG is a rare metabolic disease with multisystem impairment and variety of symptoms which determine overlapping of phenotype with other genetic disorders. The process of diagnosis is very complex and can take several years.

Genomic Analysis of Sarcomyxa edulis Reveals the Basis of Its Medicinal Properties and Evolutionary Relationships.

Yuanmo [Sarcomyxa edulis (Y.C. Dai, Niemelä & G.F. Qin) T. Saito, Tonouchi & T. Harada] is an important edible and medicinal mushroom endemic to Northeastern China. Here we report the de novo sequencing and assembly of the S. edulis genome using single-molecule real-time sequencing technology. The whole genome was approximately 35.65 Mb, with a G + C content of 48.31%. Genome assembly generated 41 contigs with an N50 length of 1,772,559 bp. The genome comprised 9,364 annotated protein-coding genes, many of which encoded enzymes involved in the modification, biosynthesis, and degradation of glycoconjugates and carbohydrates or enzymes predicted to be involved in the biosynthesis of secondary metabolites such as terpene, type I polyketide, siderophore, and fatty acids, which are responsible for the pharmacodynamic activities of S. edulis. We also identified genes encoding 1,3-β-glucan synthase and endo-1,3(4)-β-glucanase, which are involved in polysaccharide and uridine diphosphate glucose biosynthesis. Phylogenetic and comparative analyses of Basidiomycota fungi based on a single-copy orthologous protein indicated that the Sarcomyxa genus is an independent group that evolved from the Pleurotaceae family. The annotated whole-genome sequence of S. edulis can serve as a reference for investigations of bioactive compounds with medicinal value and the development and commercial production of superior S. edulis varieties.

The surprising structural and mechanistic dichotomy of membrane-associated phosphoglycosyl transferases.

Phosphoglycosyl transferases (PGTs) play a pivotal role at the inception of complex glycoconjugate biosynthesis pathways across all domains of life. PGTs promote the first membrane-committed step in the en bloc biosynthetic strategy by catalyzing the transfer of a phospho-sugar from a nucleoside diphospho-sugar to a membrane-resident polyprenol phosphate. Studies on the PGTs have been hampered because they are integral membrane proteins, and often prove to be recalcitrant to expression, purification and analysis. However, in recent years exciting new information has been derived on the structures and the mechanisms of PGTs, revealing the existence of two unique superfamilies of PGT enzymes that enact catalysis at the membrane interface. Genome neighborhood analysis shows that these superfamilies, the polytopic PGT (polyPGT) and monotopic PGT (monoPGT), may initiate different pathways within the same organism. Moreover, the same fundamental two-substrate reaction is enacted through two different chemical mechanisms with distinct modes of catalysis. This review highlights the structural and mechanistic divergence between the PGT enzyme superfamilies and how this is reflected in differences in regulation in their varied glycoconjugate biosynthesis pathways.

A Pipeline towards the Biochemical Characterization of the Arabidopsis GT14 Family.

Glycosyltransferases (GTs) catalyze the synthesis of glycosidic linkages and are essential in the biosynthesis of glycans, glycoconjugates (glycolipids and glycoproteins), and glycosides. Plant genomes generally encode many more GTs than animal genomes due to the synthesis of a cell wall and a wide variety of glycosylated secondary metabolites. The Arabidopsis thaliana genome is predicted to encode over 573 GTs that are currently classified into 42 diverse families. The biochemical functions of most of these GTs are still unknown. In this study, we updated the JBEI Arabidopsis GT clone collection by cloning an additional 105 GT cDNAs, 508 in total (89%), into Gateway-compatible vectors for downstream characterization. We further established a functional analysis pipeline using transient expression in tobacco (Nicotiana benthamiana) followed by enzymatic assays, fractionation of enzymatic products by reversed-phase HPLC (RP-HPLC) and characterization by mass spectrometry (MS). Using the GT14 family as an exemplar, we outline a strategy for identifying effective substrates of GT enzymes. By addition of UDP-GlcA as donor and the synthetic acceptors galactose-nitrobenzodiazole (Gal-NBD), β-1,6-galactotetraose (β-1,6-Gal4) and β-1,3-galactopentose (β-1,3-Gal5) to microsomes expressing individual GT14 enzymes, we verified the β-glucuronosyltransferase (GlcAT) activity of three members of this family (AtGlcAT14A, B, and E). In addition, a new family member (AT4G27480, 248) was shown to possess significantly higher activity than other GT14 enzymes. Our data indicate a likely role in arabinogalactan-protein (AGP) biosynthesis for these GT14 members. Together, the updated Arabidopsis GT clone collection and the biochemical analysis pipeline present an efficient means to identify and characterize novel GT catalytic activities.

Early uterine development in pigs

The capacity of pig uterine tissues to recognize and respond to maternal and conceptus signals determines whether pregnancy can be established and defines the environment in which embryonic and fetal growth occur. Limits of uterine capacity may be defined genetically. However, the extent to which functional uterine capacity approaches genetic potential may be determined, in part, by the success of organizational events associated with growth, morphogenesis and cytodifferentiation of uterine tissues. It is important, therefore, that these events be identified and evaluated with respect to their potential effect on adult uterine function. Histogenesis of the pig uterus begins prenatally, but is completed postnatally. Transformation of the uterine wall from histoarchitectural infancy to maturity occurs between birth and day 120. Morphogenetic events characteristic of the first 60 days of neonatal life proceed normally in gilts ovariectomized at birth. These events include appearance and proliferation of uterine glands, development of endometrial folds, and growth of the myometrium. Endometrial development during this period involves alterations in patterns of epithelial and stromal DNA synthesis, coordinated changes in the distribution and biosynthesis of extracellular matrix glycosaminoglycans and cell surface glycoconjugates, and specific alterations in patterns of uterine protein secretion. The ovary-independent, spatially coordinated nature of these events suggests that neonatal uterine development is regulated locally via dynamic cell-cell and cell-extracellular matrix interactions. The extent to which such potentially critical interactions must be preserved to ensure developmental success remains unknown. However, the normal pattern of ovary-independent cellular and molecular events associated with development of the uterine wall was disrupted by treating neonatal gilts with oestradiol valerate, and daily administration of oestrogen to gilts from birth to day 13 did not affect ovulation rate, but did reduce embryonic survival by 22% on day 45 of gestation in adults that were exposed to oestrogen neonatally. These observations support the idea that some organizational events associated with development of the neonatal uterine wall must be allowed to proceed without interruption to ensure that adult uterine function is not compromised. Efforts to identify specific developmental determinants of uterine capacity may be facilitated by examining the consequences of xenobiotically induced interruption of uterine development on adult uterine function. Such studies may also contribute to identification of uterine factors affecting embryonic survival and fetal growth.