Affinage

PCSK4

Proprotein convertase subtilisin/kexin type 4 · UniProt Q6UW60

Length
755 aa
Mass
82.8 kDa
Annotated
2026-06-10
33 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PCSK4 (PC4) is a germ cell serine endoprotease of the proprotein convertase family that is required for sperm fertilizing competence and successful early embryonic development (PMID:9192653). It localizes to acrosomal granules of round spermatids, the acrosomal ridge of elongated spermatids, and the plasma membrane overlying the acrosome of mature sperm, where it restrains premature capacitation and raises the zona pellucida threshold for the acrosome reaction while supporting zona binding (PMID:16371590). During capacitation, loss of PCSK4 produces tyrosine hyperphosphorylation and altered proteolytic processing, and the enzyme drives maturation cleavage of the fertilization-relevant substrates ADAM2 and the acrosin-binding protein ACRBP/sp32, with proacrosin autoactivation failing in its absence (PMID:19342015, PMID:21302280, PMID:22357636). PCSK4 activity is controllable through its prodomain autocatalytic cleavage site, the target of peptide and enediynyl competitive inhibitors (PMID:21302280, PMID:25881830), and is physiologically constrained by the epididymal serpin CRES, which inhibits the enzyme in an oligomeric-state-dependent manner (PMID:22827436). In somatic cells PCSK4 cannot efficiently self-activate, remaining a zymogen retained in the endoplasmic reticulum through interaction with the GRP78/BiP chaperone, so that its maturation depends on a germ cell-specific environment (PMID:21080038). Beyond reproduction, PCSK4 processes pro-IGF2 in cell-based assays, a function linked to big-IGF2 accumulation when PCSK4 expression is low (PMID:22827436, PMID:29897468).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1995 Medium

    Before functional study, the genomic position of PC4 was undefined; mapping the gene anchored it to specific mouse and human chromosomal loci, enabling subsequent genetic targeting.

    Evidence RFLP backcross panel and somatic cell hybrid Southern blotting

    PMID:7782070

    Open questions at the time
    • Locus mapping provides no functional or mechanistic information
    • No link to a disease locus established
  2. 1997 High

    It was unknown whether this germ cell convertase had a non-redundant physiological role; knockout established PCSK4 as essential for sperm fertilizing ability and for embryonic progression to blastocyst.

    Evidence Homologous-recombination knockout in mice with in vivo and in vitro fertility assays

    PMID:9192653

    Open questions at the time
    • Did not identify molecular substrates
    • Did not define the cellular step (capacitation, acrosome reaction, binding) that fails
    • No subcellular localization
  3. 2005 High

    The cellular basis of the fertilization defect was unresolved; localization to the acrosomal region combined with KO functional assays showed PCSK4 restrains premature capacitation/acrosome reaction and supports zona binding.

    Evidence Immunolocalization (IHC, IF, immuno-EM) plus capacitation, acrosome reaction and egg-binding assays in WT vs null sperm

    PMID:16371590

    Open questions at the time
    • Did not identify the proteolytic substrates mediating these effects
    • Mechanism by which PCSK4 sets the acrosome reaction threshold unknown
  4. 2009 Medium

    The signaling and proteolytic events downstream of PCSK4 were unknown; KO sperm revealed tyrosine hyperphosphorylation during capacitation and increased ADAM2 processing, tying PCSK4 to capacitation signaling and substrate cleavage.

    Evidence Capacitation time-course with phosphotyrosine and ADAM2 western blotting plus pharmacological dissection in WT vs null sperm

    PMID:19342015

    Open questions at the time
    • Direct enzyme-substrate relationship not demonstrated in this study
    • Single lab
    • Causal link between phosphorylation changes and fertilization failure not established
  5. 2011 Medium

    Whether PCSK4 enzymatic activity was directly required for sperm function was untested; a prodomain-based competitive inhibitor blocked recombinant and sperm PC activity, reduced fertilizing ability, and suppressed ADAM2 processing, supporting ADAM2 as a natural substrate.

    Evidence Recombinant enzyme inhibition (Ki determination), sperm fertilization assays with peptide inhibitor, ADAM2 processing blots

    PMID:21302280

    Open questions at the time
    • Pharmacological inhibition cannot fully exclude off-target proteases
    • Direct cleavage of ADAM2 by purified PCSK4 not reconstituted
    • Single lab
  6. 2012 Medium

    Beyond ADAM2, the substrate repertoire was unknown; proteomics identified ACRBP/sp32 as a PCSK4-dependent processing substrate and revealed failed proacrosin autoactivation and acrosome morphology defects in null sperm.

    Evidence 2D-DIGE proteomics with ACRBP/proacrosin western blots and immunolocalization in null vs WT sperm

    PMID:22357636

    Open questions at the time
    • Direct cleavage of ACRBP by PCSK4 not reconstituted in vitro
    • Single lab
    • Hierarchy among ACRBP, proacrosin and ADAM2 processing unresolved
  7. 2010 Medium

    Why PCSK4 is restricted to germ cells was unclear; expression in somatic HEK293 cells showed the zymogen is retained in the ER via GRP78/BiP and cannot self-activate, establishing a germ cell-specific maturation requirement.

    Evidence Transfection of rat/human PCSK4 in HEK293, GRP78/BiP co-IP and zymogen/processed-form blots

    PMID:21080038

    Open questions at the time
    • Germ cell-specific activating factor not identified
    • Physiological site of activation in sperm not defined
    • Single lab
  8. 2012 Medium

    Endogenous regulation of PCSK4 activity was unknown; the epididymal serpin CRES was shown to inhibit PCSK4 in an oligomeric-state-dependent manner and to block PCSK4-mediated pro-IGF2 processing, identifying a regulatory inhibitor and extending substrate scope to pro-IGF2.

    Evidence Fluorogenic substrate inhibition assays with CRES oligomers (Ki determination) and cell-based pro-IGF2 processing in trophoblast cells

    PMID:22827436

    Open questions at the time
    • In vivo relevance of CRES-PCSK4 regulation not demonstrated
    • Pro-IGF2 processing shown in heterologous cells, not native tissue
    • Single lab
  9. 2015 Medium

    To enable selective targeting, the inhibitory determinants of PCSK4 were probed; enediynyl peptides designed against the cleavage site competitively inhibited the enzyme at low µM-to-nM potency, mapping the substrate-binding site as the druggable target.

    Evidence In vitro fluorogenic-substrate enzyme kinetics establishing competitive inhibition, with cell-free and cell-culture assays

    PMID:25881830

    Open questions at the time
    • No in vivo efficacy or specificity against other convertases shown
    • Single lab
  10. 2018 Low

    Whether PCSK4-IGF2 processing operates in human pathology was unknown; in NICTH-associated solitary fibrous tumors, low PCSK4 with high IGF2 correlated with big-IGF2 accumulation, consistent with PCSK4 acting as a pro-IGF2 convertase in vivo.

    Evidence Western blot for big IGF2 in serum and IHC quantification of IGF2/PCSK4 in patient tumor tissue

    PMID:29897468

    Open questions at the time
    • Correlative only; no direct enzymatic experiment
    • Causation between PCSK4 loss and big-IGF2 not demonstrated
    • Single study

Open questions

Synthesis pass · forward-looking unresolved questions
  • The germ cell-specific factor that activates the ER-retained PCSK4 zymogen, and a reconstituted demonstration of direct substrate cleavage for ADAM2, ACRBP and pro-IGF2, remain to be defined.
  • Activation mechanism in sperm unidentified
  • No structural model of PCSK4 or its substrate complexes
  • Reconstituted enzyme-substrate cleavage not established for the physiological substrates

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 4 GO:0016787 hydrolase activity 3
Localization
GO:0005783 endoplasmic reticulum 1 GO:0005886 plasma membrane 1 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-392499 Metabolism of proteins 3 R-HSA-1474165 Reproduction 2
Partners
ACRBPADAM2CRESGRP78/BIP

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Genetic inactivation of Pcsk4 (PC4) in male mice via homologous recombination severely impairs in vivo and in vitro fertilizing ability of sperm without any evident spermatogenic abnormality, and eggs fertilized by Pcsk4-null sperm fail to develop to the blastocyst stage, establishing PCSK4 as required for fertilization and early embryonic development. Gene knockout by homologous recombination in mouse embryonic stem cells; fertility assays in vivo and in vitro Proceedings of the National Academy of Sciences of the United States of America High 9192653
2005 PCSK4 localizes to acrosomal granules of round spermatids, acrosomal ridges of elongated spermatids, and the plasma membrane overlying the acrosome of mature sperm; PCSK4-null sperm undergo capacitation at an accelerated rate, are induced to acrosome react at lower zona pellucida concentrations, and show ~50% reduced zona pellucida-binding ability, indicating PCSK4 restrains premature capacitation/acrosome reaction and supports egg binding. Immunohistochemistry, indirect immunofluorescence, immunoelectron microscopy for localization; in vitro capacitation, acrosome reaction, and egg-binding assays comparing wild-type vs. PCSK4-null sperm Biology of reproduction High 16371590
2009 PCSK4-null sperm exhibit hyperphosphorylation of tyrosine residues during capacitation (PKA-, albumin-, and calcium-dependent) and increased proteolytic processing of ADAM2 from a 46-kDa form to a 27-kDa form (cholesterol efflux-dependent), linking PCSK4 to regulation of signal transduction and proteolytic processing during capacitation. Comparative capacitation time-course assays; western blotting for phosphotyrosine and ADAM2 processing; pharmacological inhibitors of PKA, albumin chelation, calcium chelation, and cholesterol efflux in wild-type vs. Pcsk4-null sperm Fertility and sterility Medium 19342015
2011 A peptide inhibitor based on the PCSK4 prodomain autocatalytic cleavage site (proPC4(75-90)) inhibits recombinant PCSK4 activity (Ki = 5.4 µM) and suppresses sperm PC activity; inhibitor-treated sperm show dose-dependent reduction in fertilizing ability with high correlation (r > 0.9), specifically impairing capacitation and zona pellucida-induced acrosome reaction; ADAM2 processing from 45 kDa to 27 kDa during capacitation is markedly reduced, suggesting ADAM2 is a natural PCSK4 substrate. In vitro enzyme inhibition assay with recombinant PCSK4; sperm fertilization assay with peptide inhibitor; capacitation and acrosome reaction rate measurements; western blotting for ADAM2 processing Journal of cellular physiology Medium 21302280
2012 2D-DIGE proteomic analysis of PCSK4-null vs. wild-type sperm identified acrosin-binding protein (ACRBP/sp32) as a PCSK4-dependent processing substrate: ACRBP is normally processed from a 58.5 kDa precursor to a 27.5 kDa form, but this processing does not occur in PCSK4-null mice; additionally, proacrosin autoactivation fails in null sperm, and sperm head/acrosome morphological defects are observed. Two-dimensional differential in-gel electrophoresis (2D-DIGE); western blotting for ACRBP and proacrosin isoforms; immunolocalization in PCSK4-null vs. wild-type spermatozoa Molecular human reproduction Medium 22357636
2010 When expressed in HEK293 somatic cells, the bulk of PCSK4 remains as an intracellular zymogen trapped in the endoplasmic reticulum and interacts with the GRP78/BiP chaperone, indicating that proPCSK4 cannot efficiently self-activate in somatic cells and requires germ cell-specific factors or environment for maturation. Transfection of rat or human PCSK4 into HEK293 cells; co-immunoprecipitation with GRP78/BiP; western blotting for zymogen vs. processed forms Molecular and cellular biochemistry Medium 21080038
2012 The epididymal serpin CRES (cystatin-related epididymal spermatogenic protein) inhibits PCSK4 protease activity in vitro in an oligomeric-state-dependent manner: CRES dimer inhibits PCSK4 with Ki ~8 µM, while CRES monomer shows Ki > 100 µM; both forms block PCSK4-mediated processing of pro-IGF2 in placental trophoblast cells, identifying CRES as a regulatory inhibitor of PCSK4. In vitro fluorogenic substrate (Boc-RVRR-MCA) enzyme inhibition assay with recombinant PCSK4 and CRES oligomers; cell-based pro-IGF2 processing assay in human placental trophoblast cell line Current molecular medicine Medium 22827436
2015 Enediynyl peptides designed based on PCSK4 substrate cleavage site inhibit PCSK4 activity with Ki and IC50 values in low µM to high nM ranges and exhibit competitive inhibition kinetics, establishing the substrate-binding site as the target for this class of inhibitors. In vitro enzyme inhibition assay with recombinant PCSK4 using fluorogenic substrates; enzyme kinetic plots (competitive inhibition); in vitro cell-free and cell culture inhibition assays Bioorganic & medicinal chemistry letters Medium 25881830
2018 In solitary fibrous tumors causing non-islet cell tumor hypoglycemia (NICTH), imbalanced expression (high IGF2, low PCSK4) is associated with accumulation of big IGF2 in serum, consistent with PCSK4 functioning as a proteolytic convertase of pro-IGF2 in vivo. Western immunoblotting for big IGF2 in patient serum; immunohistochemical quantification of IGF2 and PCSK4 protein in tumor tissue; statistical comparison of IGF2/PCSK4 ratio between NICTH and non-NICTH groups The Journal of clinical endocrinology and metabolism Low 29897468
1995 The gene for PC4/PCSK4 was mapped to mouse chromosome 10 (near Adn and Amh loci) and to human chromosome 19 by RFLP analysis and somatic cell hybrid Southern blotting, establishing its chromosomal locus. RFLP analysis of (C57BL/6JEi x SPRET/Ei)F1 x SPRET/Ei backcross DNA panel; Southern blot analysis of human-rodent somatic cell hybrid DNA panel Genomics Medium 7782070

Source papers

Stage 0 corpus · 33 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1997 Impaired fertility in mice deficient for the testicular germ-cell protease PC4. Proceedings of the National Academy of Sciences of the United States of America 127 9192653
2008 Codon and mRNA sequence optimization of microdystrophin transgenes improves expression and physiological outcome in dystrophic mdx mice following AAV2/8 gene transfer. Molecular therapy : the journal of the American Society of Gene Therapy 96 18766174
2003 Cellular recognition of tri-/di-palmitoylated peptides is independent from a domain encompassing the N-terminal seven leucine-rich repeat (LRR)/LRR-like motifs of TLR2. The Journal of biological chemistry 66 12860988
2013 Genetics of the first seven proprotein convertase enzymes in health and disease. Current genomics 46 24396277
2005 Sperm from mice genetically deficient for the PCSK4 proteinase exhibit accelerated capacitation, precocious acrosome reaction, reduced binding to egg zona pellucida, and impaired fertilizing ability. Biology of reproduction 44 16371590
2014 Genome-wide computational analysis reveals cardiomyocyte-specific transcriptional Cis-regulatory motifs that enable efficient cardiac gene therapy. Molecular therapy : the journal of the American Society of Gene Therapy 39 25195597
2008 Proprotein convertase subtilisin/kexin type 4 in mammalian fertility: a review. Human reproduction update 35 19109312
2012 Alteration in the processing of the ACRBP/sp32 protein and sperm head/acrosome malformations in proprotein convertase 4 (PCSK4) null mice. Molecular human reproduction 33 22357636
2014 Systemic gene transfer reveals distinctive muscle transduction profile of tyrosine mutant AAV-1, -6, and -9 in neonatal dogs. Molecular therapy. Methods & clinical development 27 25105153
1995 Chromosomal assignment of the genes for proprotein convertases PC4, PC5, and PACE 4 in mouse and human. Genomics 27 7782070
2022 Therapeutic potential of highly functional codon-optimized microutrophin for muscle-specific expression. Scientific reports 22 35039573
2019 Duplications in 19p13.3 are associated with male infertility. Journal of assisted reproduction and genetics 21 31418107
2023 CRISPR-Cas9 homology-independent targeted integration of exons 1-19 restores full-length dystrophin in mice. Molecular therapy. Methods & clinical development 17 37706184
2022 Therapeutic potential of the Proprotein Convertase Subtilisin/Kexin family in vascular disease. Frontiers in pharmacology 15 36188622
2018 Imbalanced Expression of IGF2 and PCSK4 Is Associated With Overproduction of Big IGF2 in SFT With NICTH: A Pilot Study. The Journal of clinical endocrinology and metabolism 13 29897468
2021 BB-301: a silence and replace AAV-based vector for the treatment of oculopharyngeal muscular dystrophy. Molecular therapy. Nucleic acids 10 33738139
2012 Subtilisin-like proprotein convertase paired basic amino acid-cleaving enzyme 4 is required for chondrogenic differentiation in ATDC5 cells. The FEBS journal 10 22925071
2005 Synthetic bacterial lipopeptide analogs facilitate naive CD4+ T cell differentiation and enhance antigen-specific HLA-II-restricted responses. European journal of immunology 10 16052608
2021 Dose-Dependent Microdystrophin Expression Enhancement in Cardiac Muscle by a Cardiac-Specific Regulatory Element. Human gene therapy 9 33765840
2011 Enzymatic activity of sperm proprotein convertase is important for mammalian fertilization. Journal of cellular physiology 9 21302280
2009 PCSK4-null sperm display enhanced protein tyrosine phosphorylation and ADAM2 proteolytic processing during in vitro capacitation. Fertility and sterility 9 19342015
2020 Muscle overexpression of Klf15 via an AAV8-Spc5-12 construct does not provide benefits in spinal muscular atrophy mice. Gene therapy 7 32313099
2012 Dysregulation of FURIN by prostaglandin-endoperoxide synthase 2 in lung epithelial NCI-H292 cells. Molecular carcinogenesis 6 23065687
2013 Relative expression of proprotein convertases in rat ovaries during pregnancy. Journal of ovarian research 5 24330629
2012 In vitro regulatory effect of epididymal serpin CRES on protease activity of proprotein convertase PC4/PCSK4. Current molecular medicine 5 22827436
2010 The precursor to the germ cell-specific PCSK4 proteinase is inefficiently activated in transfected somatic cells: evidence of interaction with the BiP chaperone. Molecular and cellular biochemistry 5 21080038
2023 Integrated testis transcriptome and whole genome analysis of sexual maturity in Large White and Tongcheng pigs. Reproduction in domestic animals = Zuchthygiene 4 37151112
2015 Enediynyl peptides and iso-coumarinyl methyl sulfones as inhibitors of proprotein convertases PCSK8/SKI-1/S1P and PCSK4/PC4: Design, synthesis and biological evaluations. Bioorganic & medicinal chemistry letters 3 25881830
2025 Long-Term Functional Correction of Pompe Disease and Increased α-Glucosidase Expression after Gene Therapy with Novel Combinations of Muscle-Targeted Transcriptional Cis-Regulatory Elements. Human gene therapy 2 40679403
2023 CFTR and dystrophin encoding plasmids carrying both luciferase reporter gene, nuclear import specific sequences and triple helix sites. Plasmid 2 37207938
2024 A comprehensive study of common and rare genetic variants in spermatogenesis-related loci identifies new risk factors for idiopathic severe spermatogenic failure. Human reproduction open 1 39678461
2026 Novel transcriptomic alterations in poorly differentiated endometrial carcinomas: evidence from South African women. Frontiers in oncology 0 41952686
2026 AAV-mediated gene transfer of a novel microdystrophin ameliorates pathology and enhances muscle function in a mouse model of DMD. Molecular therapy. Nucleic acids 0 42003884

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