The primary structure of the beta‐subunit of the cell surface adhesion glycoproteins LFA‐1, CR3 and p150,95 and its relationship to the fibronectin receptor

The lymphocyte‐function‐associated antigen‐1 (LFA‐1), the complement receptor type 3 (CR3) and the antigen p150,95 are cell‐surface glycoproteins. They are heterodimeric complexes, each containing a unique alpha‐subunit noncovalently associated with a common beta‐subunit. We have purified the beta‐subunit from human spleen and obtained limited peptide sequences. What appears to be the complete primary structure for the fully processed beta‐subunit was obtained by cDNA sequencing of clones from a phorbol ester (PMA) stimulated U937 cDNA library. There are five possible glycosylation sites and a transmembrane segment. The sequence contains a high level of cysteine (7.6%), with 24 of the 57 cysteine residues being found in three repeating units each with eight residues. The entire primary structure has 47% identity to a subunit of a fibronectin binding protein from chicken fibroblasts. It seems that LFA‐1, CR3 and p150,95 antigens may belong to an extended family of cell surface molecules including the fibronectin binding protein.