Abstract
The GFOGER motif in collagens (O denotes hydroxyproline) represents a high-affinity binding site for all collagen-binding integrins. Other GxOGER motifs require integrin activation for maximal binding. The E318W mutant of the integrin α2β1 I domain displays a relaxed collagen specificity, typical of an active state. E318W binds more strongly than the wild-type α2 I domain to GMOGER, and forms a 2:1 complex with a homotrimeric, collagen-like, GFOGER peptide. Crystal structure analysis of this complex reveals two E318W I domains, A and B, bound to a single triple helix. The E318W I domains are virtually identical to the collagen-bound wild-type I domain, suggesting that the E318W mutation activates the I domain by destabilising the unligated conformation. E318W I domain A interacts with two collagen chains similarly to wild-type I domain (high-affinity mode). E318W I domain B makes favourable interactions with only one collagen chain (low-affinity mode). This observation suggests that single GxOGER motifs in the heterotrimeric collagens V and IX may support binding of activated integrins.
Highlights
The integrins are heterodimeric adhesion receptors, with 24 permitted pairings selected from 18 a and 8 b subunits [1]
The relative increase in prominence of the lower-affinity Toolkit peptides in these solid-phase binding experiments may be interpreted as a relaxation in the ligand specificity of a2 I E318W, resembling that of integrin a2b1 in activated platelets [15,16]
In binding experiments in which E318W and wild-type a2 I domains were applied in increasing dose to GFOGER, GMOGER and GAOGER, E318W showed a modest increase in affinity for GFOGER compared with wild-type and a substantially greater increase in affinity for GMOGER and GAOGER (Fig. 2B)
Summary
The integrins are heterodimeric adhesion receptors, with 24 permitted pairings selected from 18 a and 8 b subunits [1]. A series of loops at the distal surface of these I domains bind a Mg2+ ion that is crucially involved in the binding of ligand [4]. This arrangement is known as the metal ion-dependent adhesion site (MIDAS). The gross conformation of the extracellular region of integrins changes from a bent to an upright posture (reviewed in [5,6]), allowing unimpeded access to the ligand-binding head of the receptor. Since integrin ligands are generally macromolecular structures, this is an important aspect of the activation process, but its basis remains incompletely understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
