Cloning and analysis of monkey fertilin reveals novel alpha subunit isoforms

The fertilin complex, a heterodimeric surface membrane glycoprotein found on the head region of mammalian spermatozoa, has been reported to mediate membrane fusion with the egg plasma membrane during fertilization. We have employed PCR to generate products corresponding to monkey (Macaca fascicularis) fertilins from testis cDNA. These PCR products have been used to isolate full-length fertilin cDNA clones corresponding to both alpha and beta subunits. Both monkey fertilin alpha and beta cDNAs encode proteins which belong to an expanding family of metalloproteinase-like, disintegrin-like, cysteine-rich, mammalian proteins. Surprisingly, cDNAs for two fertilin alpha isoforms, alpha I and alpha II, were isolated, encoding proteins of 905 and 825 residues respectively. The predicted fertilin alpha isoforms share extensive identity, but differ significantly towards their N- and C-termini, suggesting the possibility of more than one type of fertilin complex in primates. Alignment of monkey alpha and beta fertilins with their respective guinea-pig counterparts suggests a high level of overall structural conservation throughout, whilst providing new insights into the domain function of each.