Characterization of human membrane cofactor protein (MCP; CD46) on spermatozoa.
Membrane cofactor protein (MCP; CD46) is a complement regulator widely expressed as four isoforms that arise via alternative splicing. On human spermatozoa, MCP is expressed on the inner acrosomal membrane and alterations of spermatozoa MCP may be associated with infertility. In rodents, expression of MCP is largely restricted to the testes. MCP on human spermatozoa has a unique M(r) pattern that we have investigated. We also characterized MCP expression in mice transgenic (tg) for human MCP. Human MCP expression in the tg mice mimics the human pattern in that it is located on the inner acrosomal membrane and has a faster M(r) than MCP expressed elsewhere. Sequencing of RT-PCR products from the testis indicates that there is not a unique male reproductive tissue specific cytoplasmic tail. Instead, human spermatozoa express MCP bearing cytoplasmic tail two, which is also utilized in most other tissues and contains several signaling motifs. Further, using N-glycosidases, we demonstrate that the unique lower molecular weight of MCP on spermatozoa is secondary to a modification in the N-linked sugars. Specifically, as the spermatozoa mature, but before they reach the epididymis, the three N-linked sugars of MCP are trimmed to less complex structures. While the purpose of this deglycosylation is unknown, we propose that it is a common feature of proteins expressed on the plasma and inner acrosomal membranes of spermatozoa and hypothesize that it is a spermatozoa specific event critical for facilitating sperm-egg interactions.
Riley
Rebecca C
RC
Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Kemper
Claudia
C
Leung
Marilyn
M
Atkinson
John P
JP
D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D003001:Cloning, Molecular; D006031:Glycosylation; D006801:Humans; D008297:Male; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D011499:Protein Processing, Post-Translational; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017423:Sequence Analysis, RNA; D013094:Spermatozoa / Q000378:metabolism*; D013737:Testis / Q000378:metabolism
D015703:Antigens, CD; C497857:CD46 protein, human; C497859:Mcp protein, mouse; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins