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. 1989 Mar;8(3):711–718. doi: 10.1002/j.1460-2075.1989.tb03430.x

Molecular cloning and characterization of the novel, human complement-associated protein, SP-40,40: a link between the complement and reproductive systems.

L Kirszbaum 1, J A Sharpe 1, B Murphy 1, A J d'Apice 1, B Classon 1, P Hudson 1, I D Walker 1
PMCID: PMC400866  PMID: 2721499

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.

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Selected References

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