title: Stereospecific interactions of proline residues in protein structures and complexes.
abstract: The constrained backbone torsion angle of a proline (Pro) residue has usually been invoked to explain its three-dimensional context in proteins. Here we show that specific interactions involving the pyrrolidine ring atoms also contribute to its location in a given secondary structure and its binding to another molecule. It is adept at participating in two rather non-conventional interactions, C-H...pi and C-H...O. The geometry of interaction between the pyrrolidine and aromatic rings, vis-à-vis the occurrence of the C-H...pi interactions has been elucidated. Some of the secondary structural elements stabilized by Pro-aromatic interactions are beta-turns, where a Pro can interact with an adjacent aromatic residue, and in antiparallel beta-sheet, where a Pro in an edge strand can interact with an aromatic residue in the adjacent strand at a non-hydrogen-bonded site. The C-H groups at the Calpha and Cdelta positions can form strong C-H...O interactions (as seen from the clustering of points) and such interactions involving a Pro residue at C' position relative to an alpha-helix can cap the hydrogen bond forming potentials of the free carbonyl groups at the helix C terminus. Functionally important Pro residues occurring at the binding site of a protein almost invariably engage aromatic residues (with one of them being held by C-H...pi interaction) from the partner molecule in the complex, and such aromatic residues are highly conserved during evolution.
authors.affiliation: Department of Biochemistry, Bose Institute, P-1/12 CIT Scheme VIIM, Calcutta 700 054, India.
authors.forename: Rajasri
authors.initials: R
authors.lastname: Bhattacharyya
authors.forename: Pinak
authors.initials: P
authors.lastname: Chakrabarti
mesh_terms: D001665:Binding Sites; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008958:Models, Molecular; D011392:Proline / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D011506:Proteins; D011392:Proline