1bho
MAC-1 I DOMAIN MAGNESIUM COMPLEX
Structural highlights
DiseaseITAM_HUMAN Genetic variations in ITGAM has been associated with susceptibility to systemic lupus erythematosus type 6 (SLEB6) [MIM:609939. Systemic lupus erythematosus (SLE) is a chronic, inflammatory and often febrile multisystemic disorder of connective tissue. It affects principally the skin, joints, kidneys and serosal membranes. It is thought to represent a failure of the regulatory mechanisms of the autoimmune system. FunctionITAM_HUMAN Integrin alpha-M/beta-2 is implicated in various adhesive interactions of monocytes, macrophages and granulocytes as well as in mediating the uptake of complement-coated particles. It is identical with CR-3, the receptor for the iC3b fragment of the third complement component. It probably recognizes the R-G-D peptide in C3b. Integrin alpha-M/beta-2 is also a receptor for fibrinogen, factor X and ICAM1. It recognizes P1 and P2 peptides of fibrinogen gamma chain. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: The integrin family of cell-surface receptors mediate cell adhesion through interactions with the extracellular matrix or other cell-surface receptors. The alpha chain of some integrin heterodimers includes an inserted 'I domain' of about 200 amino acids which binds divalent metal ions and is essential for integrin function. Lee et al. proposed that the I domain of the integrin CD11b adopts a unique 'active' conformation when bound to its counter receptor. In addition, they proposed that the lack of adhesion in the presence of Ca2+ ion reflected the stabilization of an 'inactive' I-domain conformation. We set out to independently determine the structure of the CD11 b I domain and to evaluate the structural effects of divalent ion binding to this protein. RESULTS: We have determined the X-ray structure of a new crystal form of the CD11 b I domain in the absence of added metal ions by multiple isomorphous replacement (MIR). Metal ions were easily introduced into this crystal form allowing the straight-forward assessment of the structural effects of divalent cation binding at the metal ion dependent adhesion site (MIDAS). The equilibrium binding constants for these ions were determined by titration calorimetry. The overall protein conformation and metal-ion coordination of the I domain is the same as that observed for all previously reported CD11 a I-domain structures and a CD11 b I-domain complex with Mn2+. These structures define a majority conformation. CONCLUSIONS: Addition of the cations Mg2+, Mn2+ and Cd2+ to the metal-free I domain does not induce conformational changes in the crystalline environment. Moreover, we find that Ca2+ binds poorly to the I domain which serves to explain its failure to support adhesion. We show that the active conformation proposed by Lee et al, is likely to be a construct artifact and we propose that the currently available data do not support a dramatic structural transition for the I domain during counter-receptor binding. Cation binding to the integrin CD11b I domain and activation model assessment.,Baldwin ET, Sarver RW, Bryant GL Jr, Curry KA, Fairbanks MB, Finzel BC, Garlick RL, Heinrikson RL, Horton NC, Kelley LL, Mildner AM, Moon JB, Mott JE, Mutchler VT, Tomich CS, Watenpaugh KD, Wiley VH Structure. 1998 Jul 15;6(7):923-35. PMID:9687375[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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