C-H center dot center dot center dot O hydrogen bonds in beta-sheets

A detailed analysis of the occurrence of the C-H ... O hydrogen bonds in sheet regions of proteins has been presented. 11 unique protein structures with resolution 1.3 Angstrom containing beta-sheets show a widespread presence of C-H .... O hydrogen bonds. These have average C-alpha... O, CH ... O distances and a C-alpha-H ... O angle of 3.29, 2.38 Angstrom and 143 degrees, respectively. As in the case of N-H ... O hydrogen bonds, parallel and antiparallel beta-sheet regions show the same hydrogen-bonds geometry. An inverse correlation is observed between the hydrogen-bond geometries involving the C-i(alpha)-H ... O=C and the Ni+1-H ... O=C suggesting that C-H ... O hydrogen bonds may act as an additional stabilizing factor. The propensity of different aminoacid residues to form such hydrogen bonds varies and shows a clear preference for valine and threonine. C-H ... O hydrogen bonds involving side chains also occur extensively in beta-sheet regions.