title: Molecular cloning and characterization of the novel, human complement-associated protein, SP-40,40: a link between the complement and reproductive systems.
abstract: The cDNA sequence encoding the human complement-associated protein, SP-40,40, is reported. The two chains of SP-40,40 are coded in a single open reading frame on the same mRNA molecule, indicating the existence of a biosynthetic precursor protein which matures post-synthetically by the proteolysis of at least one peptide bond. The precursor is preceded by a signal sequence for vectorial export and contains six N-linked glycosylation sites distributed equally between the two chains of the structure. The sequence of the SP-40,40 precursor bears a 77% identity to a rat sulphated glycoprotein-2 (SGP-2) which is the major secreted product of Sertoli cells. The presence of SP-40,40 within human seminal plasma at levels comparable to those in serum was demonstrated, indicating that SP-40,40 and SGP-2 are serum and seminal forms of the same protein. A sequence of 23 amino acids within the beta-chain of SP-40,40 exhibited significant homology to corresponding segments located within complement components C7, C8 and C9. The short cysteine-containing motif represented the only evidence of a possible vestigial relationship between SP-40,40 and other complement components. The precise role of SP-40,40 is not known in either blood or semen but the present findings document an intriguing link between the immune and the reproductive systems.
authors.affiliation: Department of Veterinary Preclinical Sciences, University of Melbourne, Victoria, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Kirszbaum
authors.forename: J A
authors.initials: JA
authors.lastname: Sharpe
authors.forename: B
authors.initials: B
authors.lastname: Murphy
authors.forename: A J
authors.initials: AJ
authors.lastname: d'Apice
authors.forename: B
authors.initials: B
authors.lastname: Classon
authors.forename: P
authors.initials: P
authors.lastname: Hudson
authors.forename: I D
authors.initials: ID
authors.lastname: Walker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001798:Blood Proteins / Q000235:genetics* / Q000276:immunology / Q000502:physiology; D003001:Cloning, Molecular; D051152:Clusterin; D003165:Complement System Proteins / Q000235:genetics*; D004247:DNA / Q000235:genetics; D006023:Glycoproteins / Q000235:genetics; D006801:Humans; D008297:Male; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000235:genetics; D051381:Rats; D012098:Reproduction; D012661:Semen / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001798:Blood Proteins; C495242:CLU protein, human; D051152:Clusterin; D006023:Glycoproteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D003165:Complement System Proteins; D004247:DNA