Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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Thrombostasin (TS) is a thrombin inhibitor found in the salivary glands of horn flies (Haematobia irritans). It is produced as an inactive form with a 76-amino acid propeptide in the N-terminus preceding the mature TS. A minimal recognition sequence by subtilisin-like proprotein convertases, Arg-Xaa-Xaa-Arg, is localized C-terminal to the propeptide. This study demonstrated that a gene cloned from the salivary glands of the horn fly encodes a new convertase, subsequently named horn fly proprotein convertase (HFPC), and that the recombinant HFPC expressed in insect HighFive cell culture specifically cleaves recombinant pro-thrombostasin, produced in E. coli, at the expected site. The relative cleavage efficiency of rHFPC was compared with that of recombinant human furin, a commercially available proprotein convertase. The result indicated that this newly identified proprotein convertase is of importance for the proteolytic maturation of thrombostasin, a protein secreted in horn fly saliva and used by the insect to counteract its host's haemostatic response.
Insect Biochem Mol Biol 2004 Dec
PMID:Processing of pro-thrombostasin by a recombinant subtilisin-like proprotein convertase derived from the salivary glands of horn flies (Haematobia irritans). 1554 42

In eukaryotes, many secreted proteins and peptide hormones are excised from larger precursors by calcium-dependent serine proteinases, the proprotein/prohormone convertases (PCs). These PCs cleave their protein substrates very specifically following multiple basic residues. The seven mammalian PCs and their yeast orthologue kexin are multi-domain proteinases consisting of a subtilisin-related catalytic domain, a conserved P-domain and a variable, often cysteine-rich domain, which in some PCs is followed by an additional C-terminal trans-membrane domain and a short cytoplasmic domain. The recently published crystal structures of the soluble mouse furin and yeast kexin ectodomains have revealed the relative arrangement of catalytic and P domains, the exact domain fold and the detailed architecture of the substrate binding clefts. Based on these experimental structures, we now have modelled the structures of the other human/mouse PCs. According to topology and to structure-based sequence comparisons, these other PCs closely resemble furin, with PC4, PACE4 and PC5/6 being more similar, and PC1/3, PC2 and PC7 being less similar to furin. Except for PC1 and PC2, this order of similarity is valid for the catalytic as well as for the P domains, and is almost reversed using kexin as a reference molecule. A similar order results from the number and clustering of negative charges lining the non-prime subsites, explaining the gradually decreasing requirement for basic residues N-terminal to substrate cleavage sites. The preference of the different PCs for distinct substrates seems to be governed by overall charge compensation and matching of the detailed charge distribution pattern.
J Mol Biol 2005 Jan 14
PMID:Proprotein convertase models based on the crystal structures of furin and kexin: explanation of their specificity. 1557 16

Typically, autosomal dominant familial hypercholesterolaemia (FH) is caused by mutations in the low density lipoprotein (LDL) receptor or apolipoprotein B genes that result in defective clearance of plasma LDL by the liver, but a third gene (PCSK9), encoding a putative proprotein convertase, has recently been implicated. Two independent microarray studies support a role for PCSK9 in sterol metabolism and adenoviral-mediated over-expression of PCSK9 in mouse liver depletes hepatic LDL-receptor protein, but the mechanism by which dominant mutations cause human FH is unclear. We have identified the D374Y mutant of PCSK9 in three FH families of English origin; all 12 affected individuals have unusually severe hypercholesterolaemia and require more stringent treatment than typical FH patients, who are heterozygous for defects in the LDL receptor. We have stably expressed wild-type (WT) and variant PCSK9 in McArdle-7777 rat hepatoma cells and shown by confocal microscopy that all forms of PCSK9 co-localize with protein disulphide isomerase in the ER whether or not they can be autocleaved. Expression of the proposed pathogenic variants, but not of WT, S386A or F216L PCSK9, increases secretion of apolipoprotein B100-containing lipoproteins from the cells by 2-4-fold probably by reducing the degradation of nascent protein; no differences in LDL-receptor content were observed in cells expressing WT, S386A or F216L PCSK9 and only a small reduction in cells expressing the D374Y or S127R mutants. This suggests that the variants of PCSK9 found in FH influence the secretion of apoB-containing lipoproteins, providing an explanation for the marked increase in circulating LDL in heterozygous carriers.
Hum Mol Genet 2005 May 01
PMID:Evidence for effect of mutant PCSK9 on apolipoprotein B secretion as the cause of unusually severe dominant hypercholesterolaemia. 1577 90

Proprotein convertases (PCs) are a group of Ca2+-dependent serine proteases that have homology to the endoproteases subtilisin (bacteria) and kexin (yeast). This group is comprised of less than a dozen members, known as furin/PACE, PC1/PC3, PC2, PC4, PACE4, PC5/PC6, PC7/PC8/LPC, SKI/S1P, and NARC-1/PCSK9. Four PCs (Furin, PACE4, PC5, and PC7) have been localized to several different tissues and epithelial or nervous system tumors. PCs activate their cognate substrates by limited proteolysis at the consensus sequence RXR/KR downward arrow. Many PC substrates are well known cancer-associated proteins such as growth factors, growth factor receptors, integrins, and matrix metalloproteases (MMPs). For example, IGF-1 and its receptor, TGF-beta, VEGF-C, and MT-MMPs have direct roles in tumor progression and metastasis. Furin, a well-studied member of the PC family, has been associated with enhanced invasion and proliferation in head and neck, breast, and lung cancer. Conversely, inhibition of PC activity by PDX or several PC pro-segments, resulted in reduced processing of these key cancer-related substrates in human squamous cell carcinomas (SCC), colon adenocarcinoma, and astrocytoma cell lines. In parallel to these changes in cell proliferation and invasiveness as well as metastatic ability were markedly impaired. By controlling the maturation/activation of key cancer-associated proteins, PCs act as "master switches" at different levels during tumor development and progression. The manifold effects of PCs, influencing tumor cell proliferation, motility, adhesiveness, and invasiveness, should be exploited by further developing competitive/inhibitory therapeutic strategies that would be able to neutralize simultaneously the most salient cancer cell properties.
Mol Carcinog 2005 Nov
PMID:Proprotein convertases: "master switches" in the regulation of tumor growth and progression. 1616 51

The discovery of mammalian subtilases, proprotein convertases (PCs) or subtilisin-like proprotein convertases (SPCs), in 1990 was a result of sustained efforts in searching for enzyme/s responsible for maturation of inactive protein precursors. Since then, seven PCs have so far been discovered that cleave at the carboxy-terminal of a basic amino acid characterized by the consensus sequence Arg/Lys/His-X-X/Lys/Arg-Arg downward arrow, where X denotes any amino acid other than Cys. Two additional PC subtypes--called subtilisin kexin isozyme 1 (SKI-1) or site 1 protease (S1P) and neural apoptosis regulated convertase 1 (NARC-1), also known as PCSK9--that cleave at the carboxy terminus of nonbasic amino acids were discovered later. Numerous studies revealed various important functional roles of PCs in health and diseases such as tumorigenesis, diabetes, viral infections, bacterial pathogenesis, atherosclerosis, and neurodegenarative diseases such as Alzheimer's. Owing to these findings, PCs became a promising frontier for treatment of diverse pathologies. Thus modulation of PC activity with designed inhibitors is an attractive proposition not only for intervention of diseases, but also for biochemical characterization of these enzymes. Various physiological and bioengineered proteins as well as small molecules such as peptide, peptidomimetic, and nonpeptide compounds as inhibitors of PCs have been described in the literature. Among the strategies used for design of PC inhibitors, the most successful is the one based on bioengineered serpin proteins, of which the best example is alpha1-PDX, the double mutant variant of alpha1-antitrypsin (from A(355)IPM(358) to R(355)IPR(358)). Others include small peptide inhibitors with C-terminal carboxyl function modified with a potent neucleophile or those containing pseudo or isosteric peptide bond at the scissile site of a suitable peptide substrate. Among nonpeptide PC inhibitors, the number is very limited. So far, these include 20-carbon atoms containing alicyclic diterpenes of andrographolide family and heterocyclic compounds that are ligands of Zn2+ and Cu2+ ions. Overall, these molecules display only a modest enzyme inhibition; however, they may serve as important lead structures for further development of more potent and specific nonpeptide PC inhibitors as potential therapeutic agents. Many PC inhibitors display their functional properties in proliferation, fertilization, tumorigenesis, obesity, embryogenesis, or diabetes via their inhibitory action on PC activities.
J Mol Med (Berl) 2005 Nov
PMID:Inhibitors of proprotein convertases. 1621 68

PC5 belongs to the proprotein convertase family and activates precursor proteins by cleavage at basic sites during their transit through the secretory pathway and/or at the cell surface. These precursors include prohormones, proreceptors, growth factors, adhesion molecules, and viral glycoproteins. The Pcsk5 gene encodes two alternatively spliced isoforms, the soluble PC5A and transmembrane PC5B. We have carefully analyzed the expression of PC5 in the mouse during development and in adulthood by in situ hybridization, as well as in mouse tissues and various cell lines by quantitative reverse transcription-PCR. The data show that adrenal cortex and intestine are the richest sources of PC5A and PC5B, respectively. To better define the specific physiological roles of PC5, we have generated a mouse Pcsk5(Delta4)-deficient allele missing exon 4 that encodes the catalytic Asp173. While Delta4/+ heterozygotes were healthy and fertile, genotyping of progeny obtained from Delta4/+ interbreeding indicated that Delta4/Delta4 embryos died between embryonic days 4.5 and 7.5. These data demonstrate that Pcsk5 is an essential gene.
Mol Cell Biol 2006 Jan
PMID:Deletion of the gene encoding proprotein convertase 5/6 causes early embryonic lethality in the mouse. 1635 5

Genetic analysis of the nematode Caenorhabditis elegans reveals that all dpy-5 alleles are dominant suppressors of bli-4 blistering. Molecular cloning of dpy-5 establishes that it encodes a cuticle procollagen, defects in which are responsible for the short-body, dumpy phenotype. The null mutation, e907 removes the entire coding region, whereas the dpy-5 reference allele, e61, contains a nonsense substitution. RT-PCR analysis and a dpy-5::gfp fusion show that dpy-5 is expressed only in hypodermal cells at all post-embryonic life-cycle stages. Variable expression of dpy-5 in V lineage-derived seam cells suggests an alternative regulatory mechanism in these cells. The dpy-5 gene product contains an Arg-X-X-Arg cleavage motif that could be recognized by a proprotein convertase, such as BLI-4. Mutation of this site cause a dominant dumpy phenotype suggesting Dpy-5 procollagen requires processing for normal cuticle production.
Cell Mol Life Sci 2006 May
PMID:Caenorhabditis elegans dpy-5 is a cuticle procollagen processed by a proprotein convertase. 1664 43

The Xenopus egg extract translation system has proved an ideal tool with which to study the biosynthesis of the prohormone convertases. It provides a robust coupled translation/translocation system capable of efficient translocation of any protein containing an N-terminal signal sequence into the lumen of its microsomal membranes, with cotranslational cleavage of the signal peptide. Its main advantage over rival in vitro translation systems is that it will also carry out posttranslational modification of proteins, such as N-glycosylation, and, in the case of the proprotein convertases, support autocatalytic proregion removal. The egg extract also contains an endogenous, acidic pH optimum enzyme activity, suggestive of a proprotein convertase, that can undertake limited proteolysis of precursors containing multibasic processing sites.
Methods Mol Biol 2006
PMID:Xenopus egg extracts: a model system to study proprotein convertases. 1673 25

Positional scanning-synthetic peptide combinatorial libraries (PS-SPCLs) are powerful molecular tools to identify enzyme substrate and potent inhibitory sequences and also to provide crucial information about active site determinants. PS-SPCLs have been surveyed for furin, proprotein convertase (PC)2, PC1/3, and PACE4 and proven efficient to identify potent peptidyl inhibitors in the low nanomolar range for furin and PC1/3. We report herein the screenings of nonamidated and acetylated hexapeptide PS-SPCLs for PC5/6A and PC7. The L-configuration library surveys distinctively revealed that L-Arg, L-Lys, and sometimes L-His in all six positions would generate the most potent inhibitors for both enzymes. Based on this clear polybasic preference, L-poly-Arg peptides ranging from four to nine residues were assayed. Inhibitory potency of these polybasic peptides increased with chain length, making nona-l-Arg a potent nanomolar inhibitor of PC5/6A and PC7 (Ki of 150 and 120 nM). PC5/6 and PC7 inhibition by nona-l-arginine was equivalent to that of furin (Ki of 114 nM) (J Biol Chem 275: 36741-36749, 2000). Nona-d-arginine was a more potent inhibitor of PC5/6 and PC7 than its levorotatory version (Ki of 19 and 81 nM), reminiscent of furin (Ki of 1.3 nM) (J Biol Chem 279:36788-36794, 2004). Our data indicate that certain poly-arginine peptides represent potent inhibitors targeting PCs of the constitutive secretory pathway (furin, PC5/6, and PC7). We conclude that basic residues within PC peptide inhibitors might be responsible for targeting PCs in general and for inhibitory potency, but that select amino acid changes will be necessary to acquire true specificity toward a single PC.
Mol Pharmacol 2007 Jan
PMID:Short polybasic peptide sequences are potent inhibitors of PC5/6 and PC7: Use of positional scanning-synthetic peptide combinatorial libraries as a tool for the optimization of inhibitory sequences. 1701 22

The family of the secretory proprotein convertases (PCs) comprises seven basic amino acid (aa)-specific subtilisin-like serine proteinases known as PC1/3, PC2, furin, PC4, PC5/6, PACE4 and PC7, and two other PCs, SKI-1 (subtilisin-kexin isozyme-1)/S1P (site-1 protease) and PCSK9 (proprotein convertase subtilisin kexin 9) that cleave at nonbasic residues. Except for the testicular PC4, all the other convertases are expressed in brain and peripheral organs and play a critical role in various functions including the production of diverse neuropeptides as well as growth factors and receptors, the regulation of cellular adhesion/migration, cholesterol and fatty acid homeostasis, and growth/differentiation of progenitor cells. Some of these convertases process proteins that are implicated in pathologies, including cancer malignancies, tissue regeneration, and viral infections. The implication of some of these convertases in sterol/lipid metabolism has only recently been appreciated. SKI-1/S1P activates the synthesis of cholesterol and fatty acids as well as the LDL receptor (LDLR), whereas PCSK9 inactivates the LDLR. Moreover, furin, PC5 and/or, PACE4 inactivates endothelial and lipoprotein lipases. Humans and mice exhibiting either a gain or loss of function of PCSK9 through specific point mutations or knockouts develop hypercholesterolemia and hypocholesterolemia phenotypes, respectively. A PCSK9 inhibitor in combination with statins offers a most promising therapeutic target to treat cardiovascular disorders including dyslipidemias. Specific inhibitors/modulators of the other PCs should find novel therapeutic applications in the control of PC-regulated pathologies.
J Mol Med (Berl) 2007 Jul
PMID:The proprotein convertases are potential targets in the treatment of dyslipidemia. 1735 64


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