ANALYSIS OF C-H...O HYDROGEN BONDS IN BETA SHEETS. Vasantha Pattabhi, G. Felcy Fabiola & S.Krishnaswamy⁺ Department of Biophysics, University of Madras, Guindy Campus, Madras-600025, INDIA and ⁺Bioinformatics Centre, School of Biotechnology, Madurai Kamaraj University, Madurai-625021, INDIA

C-H...O hydrogen bonds stabilising organic structures have been thoroughly studied and well documented.However,the observation of contiguous C-H...O hydrogen bonds in the beta sheet region of one of our peptide structures prompted us to analyse the beta sheet regions of proteins whose high resolution structures are known.Our analysis shows that C-H...O hydrogen bond geometry calculated using the PDB coordinates is well within the acceptable limits. As for the sequence specificity, tryptophan is the major contributor (23%) to C-H...O hydrogen bonds in antiparallel region whereas Val, Leu and Lys contribute equally to the parallel sheet region.On the whole residues other than the nonpolar ones are poor contributors to C-H...O in parallel sheets,though lysine is an exception. In the side chain main chain interactions, charged residues like Arg,Gln,His have a major role as compared to others. Twist angle of the beta sheets do not seem to affect the formation of C-H...O hydrogen bonds in a systematic way.However C-H...O and N-H..O hydrogen bond strengths appear to be correlated.