Cf. Lu et al., Locking in alternate conformations of the integrin alpha L beta 2 I domainwith disulfide bonds reveals functional relationships among integrin domains, P NAS US, 98(5), 2001, pp. 2393-2398
Citations number
33
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
We used integrin alphaL beta2 heterodimers containing I domains locked open
(active) or closed (inactive) with disulfide bonds to investigate regulato
ry interactions among domains in integrins, mAbs to the alphaL I domain and
beta2 I-like domain inhibit adhesion of wild-type alphaL beta2 to intercel
lular adhesion molecule-1. However, with alphaL beta2 containing a locked o
pen I domain, mAbs to the I domain were subdivided into subsets (i) that di
d not inhibit, and thus appear to inhibit by favoring the closed conformati
on, and tin that did inhibit, and thus appear to bind to the ligand binding
site. Furthermore, alphaL beta2 containing a locked open I domain was comp
letely resistant to inhibition by mAbs to the beta2 I-like domain, but beca
me fully susceptible to inhibition after disulfide reduction with DTT. This
finding suggests that the I-like domain indirectly contributes to ligand b
inding by regulating opening of the I domain in wild-type alphaL beta2. Con
versely, locking the I domain closed partially restrained conformational ch
ange of the I-like domain by Mn2+, as measured with mAb m24, which we map h
ere to the beta2 I-like domain. By contrast, locking the I domain closed or
open did not affect constitutive or Mn2+-induced exposure of the KIM127 ep
itope in the beta2 stalk region. Furthermore, locked open I domains, in alp
haL beta2 complexes or expressed in isolation on the cell surface, bound to
intercellular adhesion molecule-1 equivalently in Mg2+ and Mn2+. These res
ults suggest that Mn2+ activates alphaL beta2 by binding to a site other th
an the I domain, most likely the I-like domain of beta2.