Purification, molecular cloning and functional characterization of swine phosphatidylethanolamine-binding protein 4 from seminal plasma

Abstract

Phosphatidylethanolamine-binding proteins (PEBPs) are found in various species and have multiple functions. In this study, we purified the swine homolog of human PEBP4 (sPEBP4) from swine seminal plasma, cloned the sPEBP4 cDNA and functionally characterized this protein. The molecular mass of the purified protein was calculated to be 25 kDa by SDS-polyacrylamide gel electrophoresis under reducing conditions. The full-length cDNA of sPEBP4 contains 815 bp with an open reading frame of 669 bp that encodes a protein 222 residues in length. sPEBP4 contains a putative phosphatidylethanolamine-binding domain between residues 79 and 195; however, this domain did not show lipid binding activity. The overall amino acid sequence identity of PEBP4s from swine, human, mouse, bovine and canine ranges between 56.1% and 82.4%. Immunohistochemical staining and western blotting analysis showed that sPEBP4 is secreted from epithelial cells in the epididymis to the seminal plasma. To explore the role of sPEBP4 in the seminal plasma, we tested the effect of sPEBP4 on swine sperm motility. Sperms suspended in phosphate-buffered saline began to swim after the addition of purified sPEBP4, but not when swine serum albumin was added, indicating that sPEBP4 promotes sperm motility.