Figure 7
From: Cα-H···O=C hydrogen bonds contribute to the specificity of RGD cell-adhesion interactions
Bifurcated hydrogen bonding topologies. (a) The ubiquitous bifurcated hydrogen bonding topology seen in β-sheets and also in the collagen triple helix. The peptide chain is depicted with the N-terminus to the left. (b) Variation of the same bifurcated topology when the residue N-terminal to the donor N-H group is Gly, as observed in the c RGD-αVβ3 and EFB-αIIbβ3 crystal structures when Gly Hα atoms are built with standard geometry. Either one or two of the Gly Hα atoms can be in hydrogen bonding position. (c) Variation of the same bifurcated topology when the CH2 group N-terminal to the donor N-H group is replaced by another N-H group. This situation occurs for example when Gly is substituted by aza-glycine [37].