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