Folding and Function of I Domain-deleted Mac-1 and Lymphocyte Function-associated Antigen-1

• Published in: The Journal of biological chemistry Vol. 275; no. 29; pp. 21877 - 21882
• Main Authors: Yalamanchili, Padmaja, Lu, Chafen, Oxvig, Claus, Springer, Timothy A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21-07-2000; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Binding Sites; Cattle; Cell Line; Humans; integrins; LFA-1 antigen; Ligands; Lymphocyte Function-Associated Antigen-1 - chemistry; Lymphocyte Function-Associated Antigen-1 - genetics; Lymphocyte Function-Associated Antigen-1 - metabolism; Mac-1 antigen; Macrophage-1 Antigen - chemistry; Macrophage-1 Antigen - genetics; Macrophage-1 Antigen - metabolism; Protein Folding; Sequence Deletion; Structure-Activity Relationship
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M908868199

In those integrins that contain it, the I domain is a major ligand recognition site. The I domain is inserted between β-sheets 2 and 3 of the predicted β-propeller domain of the integrin α subunit. We deleted the I domain from the integrin αM and αL subunits to give I-less Mac-1 and lymphocyte function-associated antigen-1 (LFA-1), respectively. The I-less αM and αL subunits were expressed in association with the wild-type β2subunit on the surface of transfected cells and bound to all the monoclonal antibodies mapped to the putative β-propeller and C-terminal regions of the αM and αLsubunits, suggesting that the folding of these domains is independent of the I domain. I-less Mac-1 bound to the ligands iC3b and factor X, but this binding was reduced compared with wild-type Mac-1. In contrast, I-less Mac-1 did not bind to fibrinogen or denatured bovine serum albumin. Binding to iC3b and factor X by I-less Mac-1 was inhibited by the function-blocking antibody CBRM1/32, which binds to the β-propeller domain of the αM subunit. I-less LFA-1 did not bind its ligands intercellular adhesion molecule-1 and -3. Thus, the I domain is not essential for the folding, heterodimer formation, and surface expression of Mac-1 and LFA-1 and is required for binding to some ligands, but not others.