PURIFICATION AND CHARACTERIZATION OF INTEGRIN ALPHA-9-BETA-1

A new beta 1-containing integrin was isolated from rat liver by affini ty chromatography on Sepharose conjugated with the peptide GRGDSPC. Th e interaction was weakened but not abolished when the arginine and/or aspartic acid in the peptide were replaced with lysine and glutamic ac id, respectively. In contrast, the cysteine was necessary for binding of the integrin. The beta 1-associated protein, referred to as alpha 9 , had an N-terminal amino acid sequence related to but distinct from p reviously described integrin alpha-subunits. In addition, an internal peptide sequence was obtained which confirmed that the protein is a ne w member of the family of integrin alpha-subunits. An antiserum raised against a synthetic peptide corresponding to amino acids 1-16 of alph a 9 reacted specifically with this protein and was used to identify al pha 9 in several tissues. The integrin alpha 9 beta 1 was not retained on Sepharose conjugated with Englebreth-Holm-Swarm tumor (EHS)-lamini n, collagen type I, or a 105-kDa cell-binding fragment of fibronectin. However, it did bind specifically to EHS-laminin and collagen type I adsorbed to plastic microtiter wells. The sites of the interactions we re localized to fragment E8 of EHS-laminin and to cyanogen bromide fra gment 8 of collagen alpha 1(I) and were not inhibited by soluble RGD-c ontaining peptides. The results indicate that alpha 9 beta 1 is a wide ly distributed laminin/collagen receptor which may have additional, ye t unidentified ligands. (C) 1994 Academie Press, Inc.