Characterization of EPPIN's semenogelin I binding site: a contraceptive drug target

Biol Reprod. 2012 Sep 7;87(3):56. doi: 10.1095/biolreprod.112.101832. Print 2012 Sep.


Epididymal protease inhibitor (EPPIN) is found on the surface of spermatozoa and works as a central hub for a sperm surface protein complex (EPPIN protein complex [EPC]) that inhibits sperm motility on the binding of semenogelin I (SEMG1) during ejaculation. Here, we identify EPPIN's amino acids involved in the interactions within the EPC and demonstrate that EPPIN's sequence C102-P133 contains the major binding site for SEMG1. Within the same region, the sequence F117-P133 binds the EPC-associated protein lactotransferrin (LTF). We show that residues Cys102, Tyr107, and Phe117 in the EPPIN C-terminus are required for SEMG1 binding. Additionally, residues Tyr107 and Phe117 are critically involved in the interaction between EPPIN and LTF. Our findings demonstrate that EPPIN is a key player in the protein-protein interactions within the EPC. Target identification is an important step toward the development of a novel male contraceptive, and the functionality of EPPIN's residues Cys102, Tyr107, and Phe117 offers novel opportunities for contraceptive compounds that inhibit sperm motility by targeting this region of the molecule.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Binding Sites / genetics
  • Contraceptive Agents, Male* / analysis
  • Contraceptive Agents, Male* / chemistry
  • Contraceptive Agents, Male* / isolation & purification
  • Contraceptive Agents, Male* / metabolism
  • Drug Discovery
  • Humans
  • Male
  • Models, Molecular
  • Molecular Sequence Data
  • Molecular Targeted Therapy* / methods
  • Mutagenesis, Site-Directed
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Point Mutation / physiology
  • Protein Binding / genetics
  • Protein Interaction Domains and Motifs* / genetics
  • Protein Interaction Domains and Motifs* / physiology
  • Proteinase Inhibitory Proteins, Secretory / antagonists & inhibitors
  • Proteinase Inhibitory Proteins, Secretory / chemistry*
  • Proteinase Inhibitory Proteins, Secretory / genetics
  • Proteinase Inhibitory Proteins, Secretory / metabolism*
  • Seminal Vesicle Secretory Proteins / chemistry
  • Seminal Vesicle Secretory Proteins / genetics
  • Seminal Vesicle Secretory Proteins / metabolism*


  • Contraceptive Agents, Male
  • Eppin protein, human
  • Mutant Proteins
  • Proteinase Inhibitory Proteins, Secretory
  • Seminal Vesicle Secretory Proteins
  • seminal vesicle-specific antigen