title: n-->pi* interactions in proteins.
abstract: Hydrogen bonds between backbone amides are common in folded proteins. Here, we show that an intimate interaction between backbone amides also arises from the delocalization of a lone pair of electrons (n) from an oxygen atom to the antibonding orbital (pi*) of the subsequent carbonyl group. Natural bond orbital analysis predicted significant n-->pi* interactions in certain regions of the Ramachandran plot. These predictions were validated by a statistical analysis of a large, non-redundant subset of protein structures determined to high resolution. The correlation between these two independent studies is striking. Moreover, the n-->pi* interactions are abundant and especially prevalent in common secondary structures such as alpha-, 3(10)- and polyproline II helices and twisted beta-sheets. In addition to their evident effects on protein structure and stability, n-->pi* interactions could have important roles in protein folding and function, and merit inclusion in computational force fields.
authors.affiliation: School of Chemistry, University of Bristol, Bristol, United Kingdom.
authors.forename: Gail J
authors.initials: GJ
authors.lastname: Bartlett
authors.forename: Amit
authors.initials: A
authors.lastname: Choudhary
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Raines
authors.forename: Derek N
authors.initials: DN
authors.lastname: Woolfson
mesh_terms: D019295:Computational Biology; D018360:Crystallography, X-Ray; D030561:Databases, Nucleic Acid; D004151:Dipeptides / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*
chemical_list: D004151:Dipeptides; D011506:Proteins