Theoretical Analysis of the Contributions Made by CH••OH Bonds to Protein Structure

It has become increasingly apparent that there are a multitude of interactions within the context of proteins where a CH group is situated near an O atom in an arrangement that would lead one to believe that there exists a H-bond between them. Indeed, there are numerous examples in the literature where there is evidence that CH••O H-bonds play important roles in the structure of small molecules and complexes. The complexity and large size of proteins, coupled with the presence of a multitude of conventional NH••OH-bonds, however, has made such unqualified documentation difficult in these macromolecules. This paper reviews work over the last few years in which quantum calculations have been applied to this problem. Calculations are used to evaluate the properties of model systems which, while smaller than full proteins, closely approximate them. Particular attention has been paid to the CαH groups of protein residues, and in common secondary structures such as α-helices and β-sheets. The calculations detail means of estimating the energetic contribution of a given CH••O H-bond, and how this quantity depends upon the geometry of the interaction, and its relation to experimental measures, such as spectroscopic data.