Nishida Noritaka, Xie Can, Shimaoka Motomu, Cheng Yifan, Walz Thomas, Springer Timothy A
CBR Institute for Biomedical Research, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA.
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.
我们使用负染电子显微镜（EM）来检测白细胞整合素α(X)β(2)和α(L)β(2)激活所需的胞外结构域的构象变化。它们在弯曲构象和两种伸展构象之间转变，其中头部处于关闭或开放状态。伸展的整合素在α亚基膝部以及整合素表皮生长因子样（I-EGF）结构域1和2之间表现出显著的灵活性。模拟整合素α和β亚基之间近膜关联的扣环对α(X)β(2)的弯曲构象有很强的稳定作用，对α(L)β(2)的稳定作用较弱。一种小分子变构拮抗剂诱导出伸展的、开放的头部构象。一种已知可激活白细胞上β(2)整合素的Fab诱导伸展，并且只有在诱导出伸展后，激活的Fab报告分子才会结合。这些结果确立了β(2)整合素的伸展与其在免疫反应和白细胞运输中的激活之间的密切关系。
