The metalloproteinase-like, disintegrin-like, cysteine-rich (MDC) family is a large group of sequence-related proteins, first characterized in the male reproductive tract, but subsequently also identified in non-reproductive tissues. Their primary translation products are of approximately 90 kDa and each can be divided into distinct domains which show remarkable homology to reprolysins; snake venom haemorrhagic components possessing metalloproteinase and/or disintegrin domains. Several MDC proteins are abundantly-expressed in the male reproductive tract, suggesting functions in fertility. We now describe the cloning, sequence determination and characterization of transcripts encoding the human and macaque (Macaca fascicularis) orthologues of a novel member of the MDC family (eMDC II) which is abundantly-expressed in the epididymis. Unlike many MDC proteins expressed in the reproductive tract, eMDC II possesses the extended 'catalytic centre' consensus sequence characteristic of a reprolysin-like metalloproteinase. This suggests that eMDC II has proteolytic activity.

A large number of sequence-related, cysteine-rich membrane proteins containing metalloproteinase-like and disintegrin-like domains (the MDC protein family) have been identified in mammalian tissues from a variety of species. Previous studies in the macaque (Macaca fascicularis) have led to the cDNA cloning and sequence analysis of a number of MDC proteins which are abundantly expressed in the male reproductive tract. We now describe the distribution of seven of these macaque MDC transcripts in a range of different tissues. This description includes a novel macaque testis-derived MDC, tMDC III, whose full-length sequence is reported for the first time. In addition, polyclonal antisera have been used to localize a number of these MDC proteins to spermatogenic cells in testis sections, and to demonstrate their processing on the sperm surface during epididymal transit.

Five members of the MDC (metalloproteinase-like,disintegrin-like cysteine-rich domain) family of proteins (fertilin α, fertilin β, tMDC I, tMDC II and tMDC III) are expressed on the surface of macaque (Macaca fascicularis) sperm, where they have been proposed to play a role in sperm-egg binding via an interaction between their disintegrin-like domain and one or more integrins on the egg plasma membrane. Of these, two (fertilin α and tMDC I) have recently been shown to be non-functional in the human. Here we report the existence of multiple isoforms of human tMDC II transcripts in the human, all of which are also non-functional owing to the presence of deletions and in-frame termination codons, when compared with the macaque orthologue, a finding which is further supported by the lack of immunoreactivity on Western blots of human testis and sperm extracts probed with a macaque anti-tMDC II polyclonal antiserum. These results are discussed in the context of our proposed model for multiple proteins implicated in sperm-egg interactions.

Five members of the MDC (metalloproteinase-like,disintegrin-like cysteine-rich domain) family of proteins (fertilin alpha, fertilin beta, tMDC I, tMDC II and tMDC III) are expressed on the surface of macaque (Macaca fascicularis) sperm, where they have been proposed to play a role in sperm-egg binding via an interaction between their disintegrin-like domain and one or more integrins on the egg plasma membrane. Of these, two (fertilin alpha and tMDC I) have recently been shown to be non-functional in the human. Here we report the existence of multiple isoforms of human tMDC II transcripts in the human, all of which are also non-functional owing to the presence of deletions and in-frame termination codons, when compared with the macaque orthologue, a finding which is further supported by the lack of immunoreactivity on Western blots of human testis and sperm extracts probed with a macaque anti-tMDC II polyclonal antiserum. These results are discussed in the context of our proposed model for multiple proteins implicated in sperm-egg interactions.