Cleavable Signal Sequence Research Articles

Recognition and cleavage of cryptic recombination signal sequences identified from lymphoid malignancies (49.20)

Abstract Immune repertoire diversity is largely achieved by V (D) J recombination, during which antigen receptor genes are assembled from arrays of component gene segments by site-specific DNA rearrangement. This process is initiated when the RAG proteins introduce DNA double-strand breaks (DSBs) at recombination signal sequences (RSSs) abutting antigen receptor coding segments. However, the RAG proteins occasionally mistarget DNA sequences outside of antigen receptor loci and promote chromosomal translocations and deletions, which are among the major events that initiate neoplasia in lymphoid organs. Previous studies have identified various RSS-like sequences involved in chromosomal translocations, including LMO2, TAL1, Ttg-1, and Hox11, and the interstitial deletion at 1p32 involving SIL/SCL. Here we have used electrophoretic mobility shift assays and in vitro cleavage assays to study RAG-mediated binding and cleavage to the oligonucleotide substrates containing these cryptic RSSs. We find that RAG proteins can cleave LMO2, TAL1, Ttg-1, and SIL in vitro, and introduce DSBs at these sites which can be detected by ligation-mediated PCR in cell culture. In contrast, Hox11 and SCL are nicked but fail to support DSB formation both in vitro and in cell culture. These data raise the possibility that Hox11 and SCL may be cleaved by an as-yet unidentified mechanism. This research is supported by American Cancer Society grant RSG-01-020-05-LIB to P.C.S.

Mycoplasma hyopneumoniae mhp379 is a Ca2+-dependent, sugar-nonspecific exonuclease exposed on the cell surface.

Mycoplasma hyopneumoniae mhp379 is a putative lipoprotein that shares significant amino acid sequence similarity with a family of bacterial thermostable nucleases. To examine the nuclease activity of mhp379, the gene was cloned and expressed in Escherichia coli following the deletion of the amino-terminal signal sequence and prokaryotic lipoprotein cleavage site and mutagenesis of the mycoplasma TGA tryptophan codons to TGG. The recombinant fusion protein yielded a 33-kDa thrombin cleavage product, corresponding in size to the mature mhp379 protein. Exonuclease activity was indicated by agarose gel electrophoresis analysis of the reaction products that were released when different nucleic acid substrates were used. Endonuclease activity was also indicated by the digestion of closed circular plasmid DNA. The recombinant mhp379 fusion protein completely digested single-stranded DNA, double-stranded DNA (dsDNA), and RNA. The optimal reaction conditions were determined with a novel nuclease assay based on the enhancement of fluorescence of SYBR green I bound to dsDNA. Optimal activity was observed in the presence of calcium ions at a concentration of 15 mM and a pH of 9.5. No nuclease activity was observed in the absence of calcium ions. Mycoplasmas do not have the ability to synthesize nucleic acid precursors, and thus, nucleases are likely to be important in the acquisition of precursors for the synthesis of nucleic acids. Homologs of an ATP-binding cassette (ABC) transport system were identified immediately downstream of the gene encoding mhp379, and two homologs of M. pneumoniae lipoprotein multigene family 2 were also identified immediately upstream. Homologs of mhp379 were identified in the sequenced genomes of a number of mycoplasma species, and in most cases the homologous ABC transport system was identified immediately downstream of the homologous gene; in several cases a homolog of M. pneumoniae lipoprotein multigene family 2 was also identified immediately upstream. These observations suggest that mhp379 comprises part of a conserved ABC transport operon in mycoplasmas and that the exonuclease activity of mhp379 may be associated with the conserved function of the ABC transport system in the import of nucleic acid precursors. This is the first study to identify the gene and characterize the activity of a mycoplasma exonuclease.

Stable expression of Cryptosporidium parvum glycoprotein gp40/15 in Toxoplasma gondii

Cryptosporidium is a cause of diarrheal disease worldwide. Parasite glycoproteins involved in invasion of Cryptosporidium into host cells have been investigated as possible targets for effective interventions against this parasite. One of these, Cpgp40/15, is expressed as a precursor protein that is cleaved by a parasite-derived furin-like protease activity into gp15, a glycophosphatidyl inositol anchored surface protein, and gp40, that associates with gp15 and binds to host cells. Investigation of the functions of these glycoproteins requires an expression system that can produce similar glycosylation patterns to the native antigens. Previous work demonstrated that Cpgp40/15 transiently expressed in Toxoplasma gondii was appropriately localized and glycosylated. In this study, T. gondii stable transfectants expressing gp40/15, gp15, gp40 and hemagglutinin (HA) tagged gp40 were generated. T. gondii recombinant gp40HA and gp40/15 (rec Tggp40HA and rec Tggp40/15) were isolated from infected cells by HA affinity chromatography and Helix pomatia lectin affinity chromatography, respectively. Mass spectrometry confirmed that rec Tggp40-HA and native Cpgp40 were similarly glycosylated. Like native Cpgp40/15, rec Tggp40/15 could be cleaved into the gp40 and gp15 products by human furin or by a furin-like protease activity in T. gondii tachyzoite lysates. However, processing was inefficient in intact tachyzoites. Unlike the N-terminus of native Cpgp40/15, which appears to be processed following signal peptide cleavage, the N-terminus of rec Tggp40/15 began at the predicted signal sequence cleavage site, 11 amino acids upstream of the N-terminus of native Cpgp40. The ability to express and isolate appropriately glycosylated Cryptosporidium glycoproteins will enable further investigations into host–parasite interactions of this important pathogen.

Deregulation of the SecYEG Translocation Channel upon Removal of the Plug Domain

Previous studies have shown that the SecY plug is displaced from the center of the SecYEG channel during polypeptide translocation. The structural and functional consequences of the deletion of the plug are now examined. Both in vivo and in vitro observations indicate that the plug domain is not essential to the function of the translocon. In fact, deletion of the plug confers to the cell and to the membranes a Prl-like phenotype: reduced proton-motive force dependence of translocation, increased membrane insertion of SecA, diminished requirement for functional leader peptide, and weakened SecYEG subunit association. Although the plug domain does not seem essential, locking the plug in the center of the channel inactivates the translocon. Thus, the SecY plug is important to regulate the activity of the channel and to confer specificity to the translocation reaction. We propose that the plug contributes to the gating mechanism of the channel by maintaining the structure of the SecYEG complex in a compact closed state.

Biosynthesis of the dystonia-associated AAA+ ATPase torsinA at the endoplasmic reticulum

TorsinA is a widely expressed AAA(+) (ATPases associated with various cellular activities) ATPase of unknown function. Previous studies have described torsinA as a type II protein with a cleavable signal sequence, a single membrane spanning domain, and its C-terminus located in the ER (endoplasmic reticulum) lumen. However, in the present study we show that torsinA is not in fact an integral membrane protein. Instead we find that the mature protein associates peripherally with the ER membrane, most likely through an interaction with an integral membrane protein. Consistent with this model, we provide evidence that the signal peptidase complex cleaves the signal sequence of torsinA, and we show that the region previously suggested to form a transmembrane domain is translocated into the lumen of the ER. The finding that torsinA is a peripheral, and not an integral membrane protein as previously thought, has important implications for understanding the function of this novel ATPase.

Biochemical and Structural Characterization of the Secreted Chorismate Mutase (Rv1885c) from Mycobacterium tuberculosis H 37 R v : an *AroQ Enzyme Not Regulated by the Aromatic Amino Acids

The gene Rv1885c from the genome of Mycobacterium tuberculosis H37Rv encodes a monofunctional and secreted chorismate mutase (*MtCM) with a 33-amino-acid cleavable signal sequence; hence, it belongs to the *AroQ class of chorismate mutases. Consistent with the heterologously expressed *MtCM having periplasmic destination in Escherichia coli and the absence of a discrete periplasmic compartment in M. tuberculosis, we show here that *MtCM secretes into the culture filtrate of M. tuberculosis. *MtCM functions as a homodimer and exhibits a dimeric state of the protein at a concentration as low as 5 nM. *MtCM exhibits simple Michaelis-Menten kinetics with a Km of 0.5 +/- 0.05 mM and a k(cat) of 60 s(-1) per active site (at 37 degrees C and pH 7.5). The crystal structure of *MtCM has been determined at 1.7 A resolution (Protein Data Bank identifier 2F6L). The protein has an all alpha-helical structure, and the active site is formed within a single chain without any contribution from the second chain in the dimer. Analysis of the structure shows a novel fold topology for the protein with a topologically rearranged helix containing Arg134. We provide evidence by site-directed mutagenesis that the residues Arg49, Lys60, Arg72, Thr105, Glu109, and Arg134 constitute the catalytic site; the numbering of the residues includes the signal sequence. Our investigation on the effect of phenylalanine, tyrosine, and tryptophan on *MtCM shows that *MtCM is not regulated by the aromatic amino acids. Consistent with this observation, the X-ray structure of *MtCM does not have an allosteric regulatory site.

High Level Expression of a Protein Precursor for Functional Studies

In vitro analyses of type I signal peptidase activities require protein precursors as substrates. Usually, these pre-proteins are expressed in vitro and cleavage of the signal sequence is followed by SDS polyacrylamide gel electrophoresis coupled with autoradiography. Radioactive amino acids have to be incorporated in the expressed protein, since the amount of the in vitro expressed protein is usually very low and processing of the signal peptide cannot be followed by SDS polyacrylamide gel electrophoresis alone. Here we describe a rapid and simple method to express large amounts of a protein precursor in E. coli. We have analyzed the effect of ionophors as well as of azide on the accumulation of expressed protein precursors. Azide blocks the function of SecA and the ionophors dissipate the electrochemical gradient across the cytoplasmic membrane of E. coli. Addition of azide ions resulted in the formation of inclusion bodies, highly enriched with pre-apo-plastocyanine. Plastocyanine is a soluble copper protein, which can be found in the periplasmic space of cyanobacteria as well as in the thylakoid lumen of cyanobacteria and chloroplasts, and the pre-protein contains a cleavable signal sequence at its N-terminus. After purification of cyanobacterial preapo-plastocyanine, its signal sequence can be cleaved off by the E. coli signal peptidase, and protein processing was followed on Coomassie stained SDS polyacrylamide gels. We are optimistic that the presented method can be further developed and applied.

Predicting secretory protein signal sequence cleavage sites by fusing the marks of global alignments

A newly synthesized secretory protein in cells bears a special sequence, called signal peptide or sequence, which plays the role of "address tag" in guiding the protein to wherever it is needed. Such a unique function of signal sequences has stimulated novel strategies for drug design or reprogramming cells for gene therapy. To realize these new ideas and plans, however, it is important to develop an automated method for fast and accurately identifying the signal sequences or their cleavage sites. In this paper, a new method is developed for predicting the signal sequence of a query secretory protein by fusing the results from a series of global alignments through a voting system. The very high success rates thus obtained suggest that the novel approach is very promising, and that the new method may become a useful vehicle in identifying signal sequence, or at least serve as a complementary tool to the existing algorithms of this field.

Influenza A H5N1 hemagglutinin cleavable signal sequence substitutions

Eleven influenza A H5N1 hemagglutinin N-terminal cleavable signal sequences, coded by single nucleotide substitutions relative to reference A/Viet Nam/1203/2004, were identified by BLASTN search of GenBank and were characterized by molecular modeling. The signal sequences statistically segregated into two classes of states. Members of one class were uncharged and conformationally compact while members of the second class each carried a 2+ electric charge and were conformationally extended. Virtual signal sequences, not found on GenBank and based upon hypothetical transversions in the third codon, had molecular characteristics intermediate to those of the two classes of actual signal sequences. The high incidence of non-synonymous substitutions (63.6%), the high transition/transversion ratio (10/1) and the results of molecular modeling all suggest that the N-terminal cleavable signal sequence is mutationally evolving more rapidly than proteins which must assume specific conformational states in the mature influenza virion.

Rice plastidial N-glycosylated nucleotide pyrophosphatase/phosphodiesterase is transported from the ER-golgi to the chloroplast through the secretory pathway.

A nucleotide pyrophosphatase/phosphodiesterase (NPP) activity that catalyzes the hydrolytic breakdown of ADP-glucose (ADPG) has been shown to occur in the plastidial compartment of both mono- and dicotyledonous plants. To learn more about this enzyme, we purified two NPPs from rice (Oryza sativa) and barley (Hordeum vulgare) seedlings. Both enzymes are glycosylated, since they bind to concanavalin A, stain with periodic acid-Schiff reagent, and are digested by Endo-H. A complete rice NPP cDNA, designated as NPP1, was isolated, characterized, and overexpressed in transgenic plants displaying high ADPG hydrolytic activity. Databank searches revealed that NPP1 belongs to a functionally divergent group of plant nucleotide hydrolases. NPP1 contains numerous N-glycosylation sites and a cleavable hydrophobic signal sequence that does not match with the N-terminal part of the mature protein. Both immunocytochemical analyses and confocal fluorescence microscopy of rice cells expressing NPP1 fused with green fluorescent protein (GFP) revealed that NPP1-GFP occurs in the plastidial compartment. Brefeldin A treatment of NPP1-GFP-expressing cells prevented NPP1-GFP accumulation in the chloroplasts. Endo-H digestibility studies revealed that both NPP1 and NPP1-GFP in the chloroplast are glycosylated. Collectively, these data demonstrate the trafficking of glycosylated proteins from the endoplasmic reticulum-Golgi system to the chloroplast in higher plants.

Both Cleavage Products of the mCLCA3 Protein Are Secreted Soluble Proteins

Members of the chloride channels, calcium-activated (CLCA) family of proteins and in particular the murine mCLCA3 (alias gob-5) and its human ortholog hCLCA1 have been identified as clinically relevant molecules in diseases with secretory dysfunctions including asthma and cystic fibrosis. Initial studies have indicated that these proteins evoke a calcium-activated chloride conductance when transfected into human embryonic kidney cells 293 cells. However, it is not yet clear whether the CLCA proteins form chloride channels per se or function as mediators of other, yet unknown chloride channels. Here, we present a systematic biochemical analysis of the posttranslational processing and intracellular trafficking of the mCLCA3 protein. Pulse-chase experiments after metabolic protein labeling of mCLCA3-transfected COS-1 or human embryonic kidney 293 cells revealed cleavage of a primary 110-kDa mCLCA3 translation product in the endoplasmic reticulum into a 75-kDa amino-terminal and a 35-kDa carboxyl-terminal protein that were glycosylated and remained physically associated with each other. Confocal fluorescent analyses identified both cleavage products in vesicles of the secretory pathway. Neither cleavage product was associated with the cell membrane at any time. Instead, both subunits were fully secreted into the extracellular environment as a soluble complex of two glycoproteins. These results suggest that the two mCLCA3 cleavage products cannot form an anion channel on their own but may instead act as extracellular signaling molecules. Furthermore, our results point toward significant structural differences between mCLCA3 and its human ortholog, hCLCA1, which is thought to be a single, non-integral membrane protein.

VCC-1, a novel chemokine, promotes tumor growth

We have identified a novel human gene by transcriptional microarray analysis, which is co-regulated in tumors and angiogenesis model systems with VEGF expression. Isolation of cDNA clones containing the full-length VCC-1 transcript from both human and mouse shows a 119 amino acid protein with a 22 amino acid cleavable signal sequence in both species. Comparison of the protein product of this gene with hidden Markov models of all known proteins shows weak but significant homology with two known chemokines, SCYA17 and SCYA16. Northern analysis of human tissues detects a 1 kb band in lung and skeletal muscle. Murine VCC-1 expression can also be detected in lung as well as thyroid, submaxillary gland, epididymis, and uterus tissues by slot blot analysis. By quantitative real time RT-PCR 71% of breast tumors showed 3- to 24-fold up-regulation of VCC-1. In situ hybridization of breast carcinomas showed strong expression of the gene in both normal and transformed mammary gland ductal epithelial cells. In vitro, human microvascular endothelial cells grown on fibronectin increase VCC-1 expression by almost 100-fold. In addition, in the mouse angioma endothelial cell line PY4.1 the gene was over-expressed by 28-fold 6 h after induction of tube formation while quiescent and proliferating cells showed no change. VCC-1 expression is also increased by VEGF and FGF treatment, about 6- and 5-fold, respectively. Finally, 100% of mice injected with NIH3T3 cells over-expressing VCC-1 develop rapidly progressing tumors within 21 days while no growth is seen in any control mice injected with NIH3T3 cells containing the vector alone. These results strongly suggest that VCC-1 plays a role in angiogenesis and possibly in the development of tumors in some tissue types.

P-491: SED1 (Secreted protein containing a cleavable signal sequence, N-terminal Notch-like type II EGF repeats and C-terminal Discoidin/F5/8 Complement domains) is expressed on the human sperm plasma membrane

SED1 has been shown to be important to mouse sperm-egg adhesion. SED1 is made by humans and has been studied in human breast milk, but its role in human sperm-egg binding has not been evaluated. The purpose of this study was to determine if SED1 is present on human sperm and important to human sperm-egg binding.

Identification and characterization of two mature isoforms of retinoschisin in murine retina

Retinoschisin (RS) is a 24 kDa secreted protein expressed in retina and is required for the structural and functional integrity of the retina. RS has been predicted to serve as an adhesive protein but the precise molecular mechanism by which it functions in retina is not yet known. During investigations on structural and functional aspects of RS in murine retina using proteomic tools, we identified two isoforms of RS that differed in mass by 200 Da with no apparent change in charge. Mass spectra and amino acid sequence analysis of the tryptic peptides revealed that these isoforms differed by two amino acids at the N-terminus which suggested processing of RS signal sequence at two cleavage sites by signal peptidase as the basic mechanism underlying the occurrence of two mature RS isoforms in retina. Bioinformatic analysis identified two potential cleavage sites (between amino acids 21–22 and 23–24) in RS signal sequence. The flexibility of the signal peptidase to cleave at two sites is correlated to the amino acid composition of the RS signal sequence. This finding represents a rare example of a naturally occurring signal sequence cleavage at more than one site in vivo.

Mitochondrial preprotein translocases as dynamic molecular machines

Proteomic studies have demonstrated that yeast mitochondria contain roughly 1000 different proteins. Only eight of these proteins are encoded by the mitochondrial genome and are synthesized on mitochondrial ribosomes. The remaining 99% of mitochondrial precursors are encoded within the nuclear genome and after their synthesis on cytosolic ribosomes must be imported into the organelle. Targeting of these proteins to mitochondria and their import into one of the four mitochondrial subcompartments--outer membrane, intermembrane space (IMS), inner membrane and matrix--requires various membrane-embedded protein translocases, as well as numerous chaperones and cochaperones in the aqueous compartments. During the last years, several novel protein components involved in the import and assembly of mitochondrial proteins have been identified. The picture that emerges from these exciting new findings is that of highly dynamic import machineries, rather than of regulated, but static protein complexes. In this review, we will give an overview on the recent progress in our understanding of mitochondrial protein import. We will focus on the presequence translocase of the inner mitochondrial membrane, the TIM23 complex and the presequence translocase-associated motor, the PAM complex. These two molecular machineries mediate the multistep import of preproteins with cleavable N-terminal signal sequences into the matrix or inner membrane of mitochondria.

Transcription factor Pax5 (BSAP) transactivates the RAG-mediated VH-to-DJH rearrangement of immunoglobulin genes

Immunoglobulin rearrangement from variable heavy chain (V(H)) to diversity (D)-joining heavy chain (J(H)), which occurs exclusively in B lineage cells, is impaired in mice deficient for the B lineage-specific transcription factor Pax5. Conversely, ectopic Pax5 expression in thymocytes promotes the rearrangement of D(H)-proximal V(H)7183 genes. In exploring the mechanism for Pax5 regulation of V(H)-to-DJ(H) recombination, we have identified multiple Pax5 binding sites in the coding regions of human and mouse V(H) gene segments. Pax5 bound to those sites in vitro and occupied V(H) genes in early human and mouse B lineage cells. Moreover, Pax5 interacted with the recombination-activating gene 1 (RAG1)-RAG2 complex to enhance RAG-mediated V(H) recombination signal sequence cleavage and recombination of a V(H) gene substrate. These findings indicate a direct activating function for Pax5 in RAG-mediated immunoglobulin V(H)-to-DJ(H) recombination.

DNA Cleavage of a Cryptic Recombination Signal Sequence by RAG1 and RAG2: IMPLICATIONS FOR PARTIAL VH GENE REPLACEMENT

Antibody and T cell receptor genes are assembled from gene segments by V(D)J recombination to produce an almost infinitely diverse repertoire of antigen specificities. Recombination is initiated by cleavage of conserved recombination signal sequences (RSS) by RAG1 and RAG2 during lymphocyte development. Recent evidence demonstrates that recombination can occur at noncanonical RSS sites within Ig genes or at other loci, outside the context of normal lymphocyte receptor gene rearrangement. We have characterized the ability of the RAG proteins to bind and cleave a cryptic RSS (cRSS) located within an Ig V(H) gene segment. The RAG proteins bound with sequence specificity to either the consensus RSS or the cRSS. The RAG proteins nick the cRSS on both the top and bottom strands, thereby bypassing the formation of the DNA hairpin intermediate observed in RAG cleavage of canonical RSS substrates. We propose that the RAG proteins may utilize an alternative mechanism for double-stranded DNA cleavage, depending on the substrate sequence. These results have implications for further diversification of the antigen receptor repertoire as well as the role of the RAG proteins in genomic instability.

Evidence for the Role of Adenosine 5′-Triphosphate-Binding Cassette (ABC)-A1 in the Externalization of Annexin 1 from Pituitary Folliculostellate Cells and ABCA1-Transfected Cell Models

Annexin 1 (ANXA1), a 37-kDa protein, is a member of the superfamily of Ca(2+)- and phospholipid-binding annexin proteins. In the anterior pituitary, ANXA1 is expressed mainly by folliculostellate (FS) cells and mediates the early delayed feedback inhibition exerted by glucocorticoids on the release of ACTH and other pituitary hormones. It has been previously demonstrated that TtT/GF cells (a FS cell line) express and externalize ANXA1 in response to glucocorticoid treatment. However, ANXA1 lacks a cleavable signal sequence and externalization is not affected by inhibitors of the secretory pathway. We have previously shown that glyburide, an ATP-binding cassette (ABC) transporter inhibitor, inhibits the externalization of ANXA1 from TtT/GF cells and pituitary tissue. Here we investigated whether ABCA1 is involved in ANXA1 externalization. The use of the ABCA1-transporter inhibitors geranyl-geranyl pyrophosphate and sulfobromophthalein significantly inhibited ANXA1 externalization. Partial silencing of ABCA1 expression in TtT/GF cells by siRNA also significantly decreased the amount of cell surface ANXA1. However, anterior pituitary tissue from ABCA1-null mice was found to externalize ANXA1 normally. Because compensation by other ABC family members may occur in vivo, ANXA1 externalization was studied in two transfection models: Xenopus oocytes injected with ABCA1 mRNA and AtT20 D1 corticoctroph cells cotransfected with ABCA1-green fluorescent protein and ANXA1. ABCA1-expressing oocytes, but not water-injected controls, were found to externalize ANXA1. Expression of ABCA1 in AtT20 D1 cells significantly increased the amount of cell surface ANXA1, compared with mock-transfected and ANXA1-only transfected controls. Together these data provide evidence for a role of ABCA1 in ANXA1 export.

EDEM3, a Soluble EDEM Homolog, Enhances Glycoprotein Endoplasmic Reticulum-associated Degradation and Mannose Trimming

Quality control in the endoplasmic reticulum ensures that only properly folded proteins are retained in the cell through mechanisms that recognize and discard misfolded or unassembled proteins in a process called endoplasmic reticulum-associated degradation (ERAD). We previously cloned EDEM (ER degradation-enhancing alpha-mannosidase-like protein) and showed that it accelerates ERAD of misfolded glycoproteins. We now cloned mouse EDEM3, a soluble homolog of EDEM. EDEM3 consists of 931 amino acids and has all the signature motifs of Class I alpha-mannosidases (glycosyl hydrolase family 47) in its N-terminal domain and a protease-associated motif in its C-terminal region. EDEM3 accelerates glycoprotein ERAD in transfected HEK293 cells, as shown by increased degradation of misfolded alpha1-antitrypsin variant (null (Hong Kong)) and of TCRalpha. Overexpression of EDEM3 also greatly stimulates mannose trimming not only from misfolded alpha1-AT null (Hong Kong) but also from total glycoproteins, in contrast to EDEM, which has no apparent alpha1,2-mannosidase activity. Furthermore, overexpression of the E147Q EDEM3 mutant, which has the mutation in one of the conserved acidic residues essential for enzyme activity of alpha1,2-mannosidases, abolishes the stimulation of mannose trimming and greatly decreases the stimulation of ERAD by EDEM3. These results show that EDEM3 has alpha1,2-mannosidase activity in vivo, suggesting that the mechanism whereby EDEM3 accelerates glycoprotein ERAD is different from that of EDEM.

The human FK506-binding proteins: characterization of human FKBP19

Analysis of the human repertoire of the FK506-binding protein (FKBP) family of peptidyl-prolyl cis/trans isomerases has identified an expansion of genes that code for human FKBPs in the secretory pathway. There are distinct differences in tissue distribution and expression levels of each variant. In this article we describe the characterization of human FKBP19 (Entrez Gene ID: FKBP11), an FK506-binding protein predominantly expressed in vertebrate secretory tissues. The FKBP19 sequence comprises a cleavable N-terminal signal sequence followed by a putative peptidyl-prolyl cis/trans isomerase domain with homology to FKBP12. This domain binds FK506 weakly in vitro. FKBP19 mRNA is abundant in human pancreas and other secretory tissues and high levels of FKBP19 protein are detected in the acinar cells of mouse pancreas.