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：5
页码：2393-2398
DOI：10.1073/pnas.041618598
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We used integrin L{beta}2 heterodimers containing I domains locked open (active) or closed (inactive) with disulfide bonds to investigate regulatory interactions among domains in integrins. mAbs to the L I domain and {beta}2 I-like domain inhibit adhesion of wild-type L{beta}2 to intercellular adhesion molecule-1. However, with L{beta}2 containing a locked open I domain, mAbs to the I domain were subdivided into subsets (i) that did not inhibit, and thus appear to inhibit by favoring the closed conformation, and (ii) that did inhibit, and thus appear to bind to the ligand binding site. Furthermore, L{beta}2 containing a locked open I domain was completely resistant to inhibition by mAbs to the {beta}2 I-like domain, but became fully susceptible to inhibition after disulfide reduction with DTT. This finding suggests that the I-like domain indirectly contributes to ligand binding by regulating opening of the I domain in wild-type L{beta}2. Conversely, locking the I domain closed partially restrained conformational change of the I-like domain by Mn2+, as measured with mAb m24, which we map here to the {beta}2 I-like domain. By contrast, locking the I domain closed or open did not affect constitutive or Mn2+-induced exposure of the KIM127 epitope in the {beta}2 stalk region. Furthermore, locked open I domains, in L{beta}2 complexes or expressed in isolation on the cell surface, bound to intercellular adhesion molecule-1 equivalently in Mg2+ and Mn2+. These results suggest that Mn2+ activates L{beta}2 by binding to a site other than the I domain, most likely the I-like domain of {beta}2.
