Characterization of a cDNA clone coding for human testis membrane cofactor protein (MCP, CD46).
Membrane cofactor protein (MCP) is a complement regulatory protein that acts as a cofactor for the cleavage of C3b and C4b by the serine protease factor I. We have previously reported the characterization of a functional MCP molecule on the acrosomal membrane. This protein migrated as a single band with a molecular weight of 40,000 Da, which is 10,000-20,000 Da smaller than the known MCP molecules, and is devoid of N- and O-linked sugars. We have proposed that the difference in molecular weight resulted from the lack of sugars. To investigate if this is due to the absence of glycosylation sites, we have characterized a cDNA clone from a human testis cDNA library. This cDNA corresponds to a peculiar MCP form previously described, which is characterized by the presence of the serine/threonine/proline-rich exon C (STPC) and the cytoplasmic tail known as CYT2, and we conclude that the absence of mature oligosaccharide of the sperm MCP cannot be totally attributed to a defect of N- and O-glycosylation sequences but rather reflects an alteration of the mechanisms of glycosylation in spermatozoa. The presence of functional MCP on the acrosomal membrane, as well as the other complement regulatory protein, decay-accelerating factor, strongly suggests that these proteins may act concomitantly to protect the acrosome-reacted spermatozoa from the attack of the complement present in the female genital tract.
Cervoni
F
F
Institut National de la Santé et de la Recherche Médicale, Unité 210, Faculté de Médecine, Nice, France.
Fenichel
P
P
Akhoundi
C
C
Hsi
B L
BL
Rossi
B
B
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D013094:Spermatozoa / Q000276:immunology / Q000378:metabolism; D013737:Testis / Q000276:immunology / Q000378:metabolism*
D015703:Antigens, CD; C497857:CD46 protein, human; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D004247:DNA