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

EMBO J. 1989 Mar;8(3):711-8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Blood Proteins / genetics*
  • Blood Proteins / immunology
  • Blood Proteins / physiology
  • Cloning, Molecular
  • Clusterin
  • Complement System Proteins / genetics*
  • DNA / genetics
  • Glycoproteins / genetics
  • Humans
  • Male
  • Molecular Chaperones*
  • Molecular Sequence Data
  • Protein Precursors / genetics
  • Rats
  • Reproduction*
  • Semen / metabolism
  • Sequence Homology, Nucleic Acid


  • Blood Proteins
  • CLU protein, human
  • Clusterin
  • Glycoproteins
  • Molecular Chaperones
  • Protein Precursors
  • Complement System Proteins
  • DNA

Associated data

  • GENBANK/X14723