Abstract
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.
Highlights
Prostate Secretory Protein of 94 amino acids (PSP94) is secreted by the epithelial cells of the prostate [1] and is one of the major constituents present in human seminal plasma [2]
PSP94 secreted by the prostatic epithelial cells is one of the most abundant proteins present in human seminal plasma
Recent efforts have been focused towards identifying the binding partners of PSP94 in order to gain knowledge of its biological interactions. This has led to the identification of PSP94 binding proteins in serum and in seminal plasma
Summary
Prostate Secretory Protein of 94 amino acids (PSP94) is secreted by the epithelial cells of the prostate [1] and is one of the major constituents present in human seminal plasma [2]. It is a nonglycosylated, cysteine rich protein with a theoretical molecular mass of 10.7 kDa, which on SDS-PAGE (Sodium Dodecyl SulfatePolyacrylamide Gel Electrophoresis) shows an apparent molecular mass of ,17 kDa [3]. One such protein capable of interacting with PSP94 was identified and characterized to be Prostatic Acid Phosphatase (PAP) and the details are presented in this paper
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