标题：Reversibly locking a protein fold in an active conformation with a disulfide bond: Integrin αL I domains with high affinity and antagonist activity in vivo
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2001
卷号：98
期号：11
页码：6009-6014
DOI：10.1073/pnas.101130498
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The integrin L{beta}2 has three different domains in its headpiece that have been suggested to either bind ligand or to regulate ligand binding. One of these, the inserted or I domain, has a fold similar to that of small G proteins. The I domain of the M and 2 subunits has been crystallized in both open and closed conformations; however, the L I domain has been crystallized in only the closed conformation. We hypothesized that the L domain also would have an open conformation, and that this would be the ligand binding conformation. Therefore, we introduced pairs of cysteine residues to form disulfides that would lock the L I domain in either the open or closed conformation. Locking the I domain open resulted in a 9,000-fold increase in affinity to intercellular adhesion molecule-1 (ICAM-1), which was reversed by disulfide reduction. By contrast, the affinity of the locked closed conformer was similar to wild type. Binding completely depended on Mg2+. Orders of affinity were ICAM-1 > ICAM-2 > ICAM-3. The kon, koff, and KD values for the locked open I domain were within 1.5-fold of values previously determined for the L{beta}2 complex, showing that the I domain is sufficient for full affinity binding to ICAM-1. The locked open I domain antagonized L{beta}2-dependent adhesion in vitro, lymphocyte homing in vivo, and firm adhesion but not rolling on high endothelial venules. The ability to reversibly lock a protein fold in an active conformation with dramatically increased affinity opens vistas in therapeutics and proteomics.
