Prostate Secretory Protein of 94 amino acids (PSP94) binds to prostatic acid phosphatase (PAP) in human seminal plasma

PLoS One. 2013;8(3):e58631. doi: 10.1371/journal.pone.0058631. Epub 2013 Mar 4.


Prostate Secretory Protein of 94 amino acids (PSP94) is one of the major proteins present in the human seminal plasma. Though several functions have been predicted for this protein, its exact role either in sperm function or in prostate pathophysiology has not been clearly defined. Attempts to understand the mechanism of action of PSP94 has led to the search for its probable binding partners. This has resulted in the identification of PSP94 binding proteins in plasma and seminal plasma from human. During the chromatographic separation step of proteins from human seminal plasma by reversed phase HPLC, we had observed that in addition to the main fraction of PSP94, other fractions containing higher molecular weight proteins also showed the presence of detectable amounts of PSP94. This prompted us to hypothesize that PSP94 could be present in the seminal plasma complexed with other protein/s of higher molecular weight. One such fraction containing a major protein of ~47 kDa, on characterization by mass spectrometric analysis, was identified to be Prostatic Acid Phosphatase (PAP). The ability of PAP present in this fraction to bind to PSP94 was demonstrated by affinity chromatography. Co-immunoprecipitation experiments confirmed the presence of PSP94-PAP complex both in the fraction studied and in the fresh seminal plasma. In silico molecular modeling of the PSP94-PAP complex suggests that β-strands 1 and 6 of PSP94 appear to interact with domain 2 of PAP, while β-strands 7 and 10 with domain 1 of PAP. This is the first report which suggests that PSP94 can bind to PAP and the PAP-bound PSP94 is present in human seminal plasma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acid Phosphatase
  • Binding Sites
  • Chromatography, Affinity
  • Chromatography, Reverse-Phase
  • Humans
  • Immunoprecipitation
  • Male
  • Molecular Docking Simulation
  • Prostate / physiology
  • Prostatic Secretory Proteins / chemistry*
  • Prostatic Secretory Proteins / isolation & purification
  • Prostatic Secretory Proteins / metabolism
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Tyrosine Phosphatases / chemistry*
  • Protein Tyrosine Phosphatases / isolation & purification
  • Protein Tyrosine Phosphatases / metabolism
  • Semen / chemistry*


  • Prostatic Secretory Proteins
  • beta-microseminoprotein
  • Acid Phosphatase
  • prostatic acid phosphatase
  • Protein Tyrosine Phosphatases

Grant support

This work was financially supported by the Indian Council of Medical Research, New Delhi, India (NIRRH/MS/47/2012) and the Department of Biotechnology, Government of India. JHA is recipient of Junior Scholarship from the Lady Tata Memorial Trust. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.