Activation of leukocyte beta2 integrins by conversion from bent to extended conformations

Immunity. 2006 Oct;25(4):583-94. doi: 10.1016/j.immuni.2006.07.016.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies / pharmacology
  • Epidermal Growth Factor / chemistry
  • Humans
  • Integrin alphaXbeta2 / chemistry
  • Integrin alphaXbeta2 / drug effects
  • Integrin alphaXbeta2 / ultrastructure*
  • Leukocytes / immunology
  • Lymphocyte Function-Associated Antigen-1 / chemistry
  • Lymphocyte Function-Associated Antigen-1 / drug effects
  • Lymphocyte Function-Associated Antigen-1 / ultrastructure*
  • Microscopy, Electron
  • Protein Conformation
  • Protein Folding
  • Protein Structure, Tertiary


  • Antibodies
  • Integrin alphaXbeta2
  • Lymphocyte Function-Associated Antigen-1
  • Epidermal Growth Factor