Antimicrobial activity of human EPPIN, an androgen-regulated, sperm-bound protein with a whey acidic protein motif

Biol Reprod. 2004 Nov;71(5):1484-90. doi: 10.1095/biolreprod.104.031567. Epub 2004 Jun 30.


The role of epididymal sperm-binding proteins in reproductive tract immunity is now well recognized in addition to their role in sperm maturation. Spermatozoa acquire forward motility and fertilizing ability during their passage through the epididymis, where they acquire a wide variety of proteins belonging to different classes. Previously, we demonstrated that EPPIN (epididymal protease inhibitor), an androgen-regulated, sperm-binding protein containing protease-inhibitory motifs, is expressed specifically in the testis and epididymis. In the present study, we investigated the antibacterial activity of EPPIN against Escherichia coli and the mechanism of antimicrobial action. EPPIN exhibited dose- and time-dependent antibacterial activity that was relatively insensitive to salt. However, EPPIN lost its antibacterial activity completely on reduction and alkylation of its cysteines, indicating the importance of disulfide bonds for its activity. EPPIN permeabilized the outer and inner membranes of E. coli, which is consistent with its ability to induce striking morphological alterations of E. coli membranes as shown by scanning electron microscopy. EPPIN did not cause disruption of eukaryotic membranes in the rat erythrocyte hemolytic assay. The present results indicate that EPPIN has a role in the innate immune system of human epididymis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Androgens / physiology*
  • Animals
  • Anti-Bacterial Agents / metabolism*
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure
  • Dose-Response Relationship, Drug
  • Erythrocytes / drug effects
  • Escherichia coli / drug effects
  • Escherichia coli / metabolism
  • Escherichia coli / ultrastructure
  • Hemolysis
  • Humans
  • Male
  • Microscopy, Electron, Scanning
  • Milk Proteins / genetics*
  • Molecular Sequence Data
  • Proteinase Inhibitory Proteins, Secretory
  • Proteins / administration & dosage
  • Proteins / genetics
  • Proteins / pharmacology
  • Proteins / physiology*
  • Rats
  • Spermatozoa / metabolism*
  • Time Factors


  • Androgens
  • Anti-Bacterial Agents
  • Eppin protein, human
  • Milk Proteins
  • Proteinase Inhibitory Proteins, Secretory
  • Proteins
  • whey acidic proteins