Interaction of the alpha 2A domain of integrin with small collagen fragments

We here present a detailed study of the ligand-receptor interactions between single and triple-helical strands of collagen and the alpha 2A domain of integrin (alpha 2A), providing valuable newinsights into the mechanisms and dynamics of collagen-integrin binding at a sub-molecular level. The occurrence of single and triple-helical strands of the collagen fragments was scrutinized with atom force microscopy (AFM) techniques. Strong interactions of the triple-stranded fragments comparable to those of collagen can only be detected for the 42mer triple-helical collagen-like peptide under study (which contains 42 amino acid residues per strand) by solid phase assays as well as by surface plasmon resonance (SPR) measurements. However, changes in NMR signals during titration and characteristic saturation transfer difference (STD) NMR signals are also detectable when alpha 2A is added to a solution of the 21mer single-stranded collagen fragment. Molecular dynamics (MD) simulations employing different sets of force field parameters were applied to study the interaction between triple-helical or single-stranded collagen fragments with alpha 2A. It is remarkable that even single-stranded collagen fragments can form various complexes with alpha 2A showing significant differences in the complex stability with identical ligands. The results of MD simulations are in agreement with the signal alterations in our NMR experiments, which are indicative of the formation of weak complexes between single-stranded collagen and alpha 2A in solution. These results provide useful information concerning possible interactions of alpha 2A with small collagen fragments that are of relevance to the design of novel therapeutic A-domain inhibitors.