title: Activation of leukocyte beta2 integrins by conversion from bent to extended conformations.
abstract: We used negative stain electron microscopy (EM) to examine the conformational changes in the ectodomains required for activation of the leukocyte integrins alpha(X)beta(2) and alpha(L)beta(2). They transitioned between a bent conformation and two extended conformations in which the headpiece was in either a closed or an open state. Extended integrins exhibited marked flexibility at the alpha subunit genu and between integrin epidermal growth factor-like (I-EGF) domains 1 and 2. A clasp to mimic juxtamembrane association between the integrin alpha and beta subunits stabilized the bent conformation strongly for alpha(X)beta(2) and less so for alpha(L)beta(2). A small molecule allosteric antagonist induced the extended, open headpiece conformation. A Fab known to activate beta(2) integrins on leukocytes induced extension, and a Fab reporter of activation bound only after extension had been induced. The results establish an intimate relationship between extension of beta(2) integrins and their activation in immune responses and leukocyte trafficking.
authors.affiliation: CBR Institute for Biomedical Research, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA.
authors.forename: Noritaka
authors.initials: N
authors.lastname: Nishida
authors.forename: Can
authors.initials: C
authors.lastname: Xie
authors.forename: Motomu
authors.initials: M
authors.lastname: Shimaoka
authors.forename: Yifan
authors.initials: Y
authors.lastname: Cheng
authors.forename: Thomas
authors.initials: T
authors.lastname: Walz
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000737:chemistry; D006801:Humans; D016167:Integrin alphaXbeta2 / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*; D007962:Leukocytes / Q000276:immunology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*; D008854:Microscopy, Electron; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary
chemical_list: D000906:Antibodies; D016167:Integrin alphaXbeta2; D016169:Lymphocyte Function-Associated Antigen-1; D004815:Epidermal Growth Factor