CLONING, PRIMARY STRUCTURE AND PROPERTIES OF A NOVEL HUMAN INTEGRIN BETA-SUBUNIT

The originally described integrin β subunits that define the three subfamilies of integrin heterodimers are β1, β2 and β3. In this paper, we describe the isolation of a cDNA coding for a novel human integrin β subunit, designated as β5. The β5 cDNA was isolated from a human thymic epithelial cell library, using oligonucleotide probes that were designed from a region highly conserved among the known β1, β2 and β3 sequences. The β5 cDNA codes for 799 (or 796) amino acids, including a 23 amino acid leader sequence. There are 776 (or 773) amino acids in the mature protein, which includes a long extracellular domain of 696 amino acids, a transmembrane domain and an intracellular C-terminal domain of 57 amino acids. The β5 sequence resembled the known β3, β1 and β2 sequences by 55, 43 and 38%, respectively, including conservation of 56/56 cysteines. Rabbit antiserum was prepared against a 20 amino acid synthetic peptide predicted from the β5 C-terminal sequence. This serum immunoprecipitated a β5 protein that was 100000 M(r) (reduced) and 95000 M(r) (nonreduced). Only a single α subunit was detected in association with β5, and that α subunit was immunochemically indistinguishable from the α(v) subunit previously found as part of the vitronectin receptor complex. By immunoprecipitation, β5 was most prevalent on carcinoma cell lines, was also present on hepatoma and fibroblast cell lines, and was absent fom lymphoblastoid cells and platelets.