Novel sperm-binding proteins of epididymal origin contain four fibronectintype II-modules

Novel fibronectin type II (Fn2)module proteins were cloned from human and c anine epididymal cDNA libraries. cDNA sequences predicted a highly conserve d protein family, related but not homologous to ungulate seminal plasma pro teins (approximately 50% sequence identity), and the first known examples o f proteins with four tandemly arranged Fn2-domains. By Northern blot and in situ hybridization analyses the encoding mRNAs were shown to be abundant p roducts of the epididymal duct epithelium, but not detectable in other tiss ues. Homologous mRNAs were identified in the epididymides of various mammal s, representing members of this novel protein family of epididymal origin. Within the Fn2-module-encoding stretches, species homologues displayed >85% sequence identity, but showed high variability at their predicted N-termin i. An antipeptide antiserum in Western blot analyses detected 30-35 kDa imm unoreactive protein bands in epididymal tissue, cauda epididymidal fluid, a nd sperm membrane protein preparations. The tandem arrangement of increasin g numbers of Fn2-modules might functionally correspond to the tendency to f orm oligomers that has been described for lipid-binding proteins. (C) 2001 Wiley-Liss, Inc.