A porcine homolog of the major secretory protein of human epididymis, HE1,specifically binds cholesterol

A porcine homolog of the major secretory protein of human epididymis, HE1, was for the first time purified from the porcine cauda epididymal fluid. Th e HE1 homolog was secreted into the epididymal fluid as a 19-kDa glycoprote in, whose sugar moiety was gradually processed to form a 16-kDa protein dur ing transit through the epididymis. The HEI homolog mRNA was detected only in the caput and corpus epididymis among the porcine tissues examined. The purified HEI homolog specifically bound cholesterol with high affinity (K-d = 2.3 mu M). The binding stoichiometry was determined to be 0.94 mol/mol, suggesting that 1 mol of cholesterol binds to 1 mol of the protein, It was also found that the HE1 homolog is a major cholesterol-binding protein in t he porcine epididymal fluid. The possibility that the HE1 homolog is involv ed in the regulation of the lipid composition of the sperm membranes during the maturation in epididymis is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.