Molecular cloning of S-protein, a link between complement, coagulation and cell-substrate adhesion

Area of Science:

• Molecular Biology
• Biochemistry
• Immunology

Background:

• Human S-protein's function and identity were previously unclear.
• Monoclonal antibodies were available for S-protein detection.

Purpose of the Study:

• To isolate and characterize cDNA clones encoding human S-protein.
• To determine the complete amino acid sequence of S-protein.
• To elucidate the relationship between S-protein, somatomedin B, and vitronectin.

Main Methods:

• Screening of a lambda gt11 cDNA library using monoclonal antibodies.
• DNA sequencing of isolated cDNA clones.
• Sequence analysis and comparison with known proteins.

Main Results:

• Isolated authentic S-protein cDNA clones.
• Determined the complete open reading frame for S-protein (459 amino acids) with a cleaved leader peptide.
• Identified significant sequence homology between S-protein and vitronectin (serum spreading factor).
• Found the N-terminal 42 of 44 residues identical to somatomedin B peptide, suggesting S-protein is its precursor.

Conclusions:

• S-protein and vitronectin are identical.
• S-protein functions as the precursor to somatomedin B.
• This identity has implications for the coagulation and complement pathways.