We have determined the structure of the human integrin α1I domain bound to a 
triple-helical collagen peptide. The structure of the α1I-peptide complex was 
investigated using data from NMR, small angle x-ray scattering, and size 
exclusion chromatography that were used to generate and validate a model of the 
complex using the data-driven docking program, HADDOCK (High Ambiguity Driven 
Biomolecular Docking). The structure revealed that the α1I domain undergoes a 
major conformational change upon binding of the collagen peptide. This involves 
a large movement in the C-terminal helix of the αI domain that has been 
suggested to be the mechanism by which signals are propagated in the intact 
integrin receptor. The structure suggests a basis for the different binding 
selectivity observed for the α1I and α2I domains. Mutational data identify 
residues that contribute to the conformational change observed. Furthermore, 
small angle x-ray scattering data suggest that at low collagen peptide 
concentrations the complex exists in equilibrium between a 1:1 and 2:1 
α1I-peptide complex.