ZP3 explained

Zona pellucida sperm-binding protein 3, also known as zona pellucida glycoprotein 3 (Zp-3) or the sperm receptor, is a ZP module-containing protein that in humans is encoded by the ZP3 gene.^[1] ZP3 is the glycoprotein in the zona pellucida most important for inducting the acrosome reaction of sperm cells at the beginning of fertilization.^[2]

Function

The zona pellucida (ZP) is a specialized extracellular matrix that surrounds the oocyte and early embryo. It is composed of three or four glycoproteins (ZP1-4) with various functions during oogenesis, fertilization and preimplantation development. The protein encoded by this gene is a major structural component of the ZP and functions in primary binding and stimulation of the sperm acrosome reaction. The nascent protein contains a N-terminal signal peptide sequence, a conserved "ZP domain" module, a consensus furin cleavage site (CFCS), a polymerization-blocking external hydrophobic patch (EHP), and a C-terminal transmembrane domain. Cleavage at the CFCS separates the mature protein from the EHP, allowing it to incorporate into nascent ZP filaments. A variation in the last exon of this gene has previously served as the basis for an additional ZP3 locus; however, sequence and literature review reveals that there is only one full-length ZP3 locus in the human genome. Another locus encoding a bipartite transcript designated POMZP3 contains a duplication of the last four exons of ZP3, including the above described variation, and maps closely to this gene.^[1]

In mice, ZP3 (more specifically the portion in its exon 7) is the single ZP protein that is sufficient and necessary for sperm binding in vitro,^[2] but is insufficient for fertilization in vivo.^[3] In humans, ZP1, ZP3, and ZP4 all appear partially responsible for starting the acrosome reaction.^[4]

Orthologs of these genes are found throughout Vertebrata. The western clawed frog appears to have two orthologs, and the sea lamprey has seven.^[5]

3D Structure

X-ray crystallographic studies of the N-terminal half of mammalian ZP3 ^[6] as well as its full-length avian homolog ^[7] revealed that the protein's ZP module consists of two immunoglobulin-like domains, ZP-N and ZP-C. The latter, which contains EHP as well as a ZP3-specific subdomain, interacts with the ZP-N domain of a second molecule to generate an antiparallel homodimeric arrangement required for protein secretion.^[7]

Mutations

The Zona Pellucida (ZP) is a complex matrix of glycoprotein that surrounds the oocyte and plays a crucial role in the attachment of sperm during reproduction. Ultimately, through the facilitation of sperm binding and the initiation of the acrosome reaction, the ZP proteins are essential to reproduction and have an important impact on fertility. Research through the Journal of Cellular and Molecular Medicine conducted experiments to determine the mechanisms surrounding possible mutations to the ZP gene and how they would impact fertility.^[8] By performing whole-exome sequencing they isolated a genome that had a mutation in the ZP3 and the ZP1 genes. They then transfected these genes into HeLa cell cultures and ran a variety of tests to isolate the consequences of these mutations. The authors wrote this regarding their results:

“The results indicate that the mutations are involved in the reduced secretion of ZP1 and ZP3 and leading to connection failure of the ZP filaments in vitro. The data suggest a potential that the mutations may be involved in the lacking ZP phenotype, which need to be further investigated in vivo.” (Cao, Qiqi, et al.)

It is clear that that the ZP proteins are crucial to expressing a correct ZP phenotype in humans, in which all of the ZP proteins 1-4 are properly functioning. Without this interface of proper protein function, sperm binding is inhibited, and fertility is compromised.

References

^[9]

Further reading

• Bansal P, Chakrabarti K, Gupta SK . Functional activity of human ZP3 primary sperm receptor resides toward its C-terminus . Biol. Reprod. . 81 . 1 . 7–15 . 2009 . 19246320 . 10.1095/biolreprod.108.074716 . free .
• Bleil JD, Wassarman PM . Mammalian sperm-egg interaction: identification of a glycoprotein in mouse egg zonae pellucidae possessing receptor activity for sperm . Cell . 20 . 3 . 873–82 . 1980 . 7418009 . 10.1016/0092-8674(80)90334-7 . 29105880 .
• Caballero-Campo P, Chirinos M, Fan XJ, etal . Biological effects of recombinant human zona pellucida proteins on sperm function . Biol. Reprod. . 74 . 4 . 760–8 . 2006 . 16407501 . 10.1095/biolreprod.105.047522 . free .
• Chamberlin ME, Dean J . Human homolog of the mouse sperm receptor . Proc. Natl. Acad. Sci. U.S.A. . 87 . 16 . 6014–8 . 1990 . 2385582 . 10.1073/pnas.87.16.6014 . 54462. 1990PNAS...87.6014C . free .
• Chiu PC, Wong BS, Chung MK, etal . Effects of native human zona pellucida glycoproteins 3 and 4 on acrosome reaction and zona pellucida binding of human spermatozoa . Biol. Reprod. . 79 . 5 . 869–77 . 2008 . 18667750 . 10.1095/biolreprod.108.069344 . free .
• Choudhury S, Ganguly A, Chakrabarti K, etal . DNA vaccine encoding chimeric protein encompassing epitopes of human ZP3 and ZP4: immunogenicity and characterization of antibodies . J. Reprod. Immunol. . 79 . 2 . 137–47 . 2009 . 19004505 . 10.1016/j.jri.2008.09.002 .
• Dell A, Chalabi S, Easton RL, etal . Murine and human zona pellucida 3 derived from mouse eggs express identical O-glycans . Proc. Natl. Acad. Sci. U.S.A. . 100 . 26 . 15631–6 . 2003 . 14673092 . 10.1073/pnas.2635507100 . 307619. 2003PNAS..10015631D . free .
• Florman HM, Wassarman PM . O-linked oligosaccharides of mouse egg ZP3 account for its sperm receptor activity . Cell . 41 . 1 . 313–24 . 1985 . 2986849 . 10.1016/0092-8674(85)90084-4 . 7133279 .
• Furlong LI, Harris JD, Vazquez-Levin MH . Binding of recombinant human proacrosin/acrosin to zona pellucida (ZP) glycoproteins. I. Studies with recombinant human ZPA, ZPB, and ZPC . Fertil. Steril. . 83 . 6 . 1780–90 . 2005 . 15950651 . 10.1016/j.fertnstert.2004.12.042 . free .
• Gook DA, Edgar DH, Borg J, Martic M . Detection of zona pellucida proteins during human folliculogenesis . Hum. Reprod. . 23 . 2 . 394–402 . 2008 . 18033806 . 10.1093/humrep/dem373 . free .
• Han L, Monné M, Okumura H, Schwend T, Cherry AL, Flot D, Matsuda T, Jovine L . Insights into egg coat assembly and egg-sperm interaction from the X-ray structure of full-length ZP3 . Cell . 143 . 3 . 404–15 . 2010 . 20970175 . 10.1016/j.cell.2010.09.041 . 18583237 . free . 11563/8931 . free .
• Jovine L, Qi H, Williams Z, Litscher E, Wassarman PM . The ZP domain is a conserved module for polymerization of extracellular proteins . Nat. Cell Biol. . 4 . 6 . 457–61 . 2002 . 12021773 . 10.1038/ncb802 . 11575790 .
• Jovine L, Qi H, Williams Z, Litscher ES, Wassarman PM . A duplicated motif controls assembly of zona pellucida domain proteins . Proc. Natl. Acad. Sci. U.S.A. . 101 . 16 . 5922–7 . 2004 . 15079052 . 10.1073/pnas.0401600101 . 395899. 2004PNAS..101.5922J . free .
• Kiefer SM, Saling P . Proteolytic processing of human zona pellucida proteins . Biol. Reprod. . 66 . 2 . 407–14 . 2002 . 11804956 . 10.1095/biolreprod66.2.407. free .
• Monné M, Han L, Schwend T, Burendahl S, Jovine L . Crystal structure of the ZP-N domain of ZP3 reveals the core fold of animal egg coats . Nature . 456 . 7222 . 653–7 . 2008 . 19052627 . 10.1038/nature07599 . 2008Natur.456..653M . 11563/8930 . 4430083 . free .
• Ni Y, Li K, Xu W, etal . Acrosome reaction induced by recombinant human zona pellucida 3 peptides rhuZP3a22 approximately 176 and rhuZP3b177 approximately 348 and their mechanism . J. Androl. . 28 . 3 . 381–8 . 2007 . 17192598 . 10.2164/jandrol.106.001289 . free .
• Qi H, Williams Z, Wassarman PM . Secretion and assembly of zona pellucida glycoproteins by growing mouse oocytes microinjected with epitope-tagged cDNAs for mZP2 and mZP3 . Mol. Biol. Cell . 13 . 2 . 530–41 . 2002 . 11854410 . 10.1091/mbc.01-09-0440 . 65647.
• Rankin T, Dean J . The zona pellucida: using molecular genetics to study the mammalian egg coat . Rev. Reprod. . 5 . 2 . 114–21 . 2000 . 10864856 . 10.1530/ror.0.0050114. free .
• Törmälä RM, Jääskeläinen M, Lakkakorpi J, etal . Zona pellucida components are present in human fetal ovary before follicle formation . Mol. Cell. Endocrinol. . 289 . 1–2 . 10–5 . 2008 . 18502569 . 10.1016/j.mce.2008.01.029 . 3455166 .
• van Duin M, Polman JE, Verkoelen CC, Bunschoten H, Meyerink JH, Olijve W, Aitken RJ . Cloning and characterization of the human sperm receptor ligand ZP3: evidence for a second polymorphic allele with a different frequency in the Caucasian and Japanese populations . Genomics . 14 . 4 . 1064–70 . December 1992 . 1478648 . 10.1016/S0888-7543(05)80130-2.
• Wassarman PM, Jovine L, Litscher ES . A profile of fertilization in mammals . Nat. Cell Biol. . 3 . 2 . E59–64 . 2001 . 11175768 . 10.1038/35055178 . 6172791 .
• Zhao M, Boja ES, Hoodbhoy T, etal . Mass spectrometry analysis of recombinant human ZP3 expressed in glycosylation-deficient CHO cells . Biochemistry . 43 . 38 . 12090–104 . 2004 . 15379548 . 10.1021/bi048958k .
• Zhao M, Gold L, Ginsberg AM, etal . Conserved furin cleavage site not essential for secretion and integration of ZP3 into the extracellular egg coat of transgenic mice . Mol. Cell. Biol. . 22 . 9 . 3111–20 . 2002 . 11940668 . 10.1128/MCB.22.9.3111-3120.2002 . 133755.

Notes and References

1. Web site: Entrez Gene: zona pellucida glycoprotein 3 (sperm receptor).
2. Zona pellucida glycoprotein ZP3 and fertilization in mammals . 19504560 . 2009 . Litscher . E. S. . Williams . Z. . Wassarman . P. M. . Molecular Reproduction and Development . 76 . 10 . 933–941 . 10.1002/mrd.21046 . 21186053 .
3. Avella MA, Baibakov B, Dean J . A single domain of the ZP2 zona pellucida protein mediates gamete recognition in mice and humans. . J Cell Biol . 205 . 6 . 801–809 . 24934154 . 10.1083/jcb.201404025 . 4068139 . 2014 . Female mice that form a zona pellucida lacking ZP2 are sterile.
4. Gupta . SK . Bhandari . B . Acrosome reaction: relevance of zona pellucida glycoproteins. . Asian journal of andrology . January 2011 . 13 . 1 . 97-105 . 10.1038/aja.2010.72 . 21042299 . 3739397.
5. Web site: EggNOG Database Orthology predictions and functional annotation . eggnogdb.embl.de . 5 March 2019 . 4 March 2019 . https://web.archive.org/web/20190304080601/http://eggnogdb.embl.de/#/app/results?seqid=P21754&target_nogs=ENOG410II9V . dead .
6. Monné M, Han L, Schwend T, Burendahl S, Jovine L . Crystal structure of the ZP-N domain of ZP3 reveals the core fold of animal egg coats . Nature . 456 . 7222 . 653–7 . 2008 . 19052627 . 10.1038/nature07599 . 2008Natur.456..653M . 11563/8930 . 4430083 . free .
7. Han L, Monné M, Okumura H, Schwend T, Cherry AL, Flot D, Matsuda T, Jovine L . Insights into egg coat assembly and egg-sperm interaction from the X-ray structure of full-length ZP3 . Cell . 143 . 3 . 404–15 . 2010 . 20970175 . 10.1016/j.cell.2010.09.041 . 18583237 . free . 11563/8931 . free .
8. Cao . Qiqi . Zhao . Chun . Zhang . Xiaolan . Zhang . Heng . Lu . Qianneng . Wang . Congjing . Hu . Yue . Ling . Xiufeng . Zhang . Junqiang . Huo . Ran . 2020-06-22 . Heterozygous mutations in ZP1 and ZP3 cause formation disorder of ZP and female infertility in human . Journal of Cellular and Molecular Medicine . en . 24 . 15 . 8557–8566 . 10.1111/jcmm.15482 . 1582-1838 . 7412702 . 32573113.
9. Cao, Qiqi, et al. “Heterozygous Mutations in ZP1 and ZP3 Cause Formation ...” Journal of Cellular and Molecular Medicine, Wiley Online Library, 22 June 2020, onlinelibrary.wiley.com/doi/10.1111/jcmm.15482.