An electronic effect on protein structure.
The well-known preference of the peptide bond for the trans conformation has been attributed to steric effects. Here, we show that a proline residue with an N-formyl group (H(i-1)-C'(i-1)=O(i-1)), in which H(i-1) presents less steric hindrance than does O(i-1), likewise prefers a trans conformation. Thus, the preference of the peptide bond for the trans conformation cannot be explained by steric effects alone. Rather, an n --> pi* interaction between the oxygen of the peptide bond (O(i-1)), and the subsequent carbonyl carbon in the polypeptide chain (C'(i)) also contributes to this preference. The O(i-1) and C'(i) distance and O(i-1).C'(i)=O(i) angle are especially favorable for such an n --> pi* interaction in a polyproline II helix. We propose that this electronic effect provides substantial stabilization to this and other elements of protein structure.
Hinderaker
Matthew P
MP
Department of Chemistry and Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Raines
Ronald T
RT
D000577:Amides / Q000138:chemical synthesis; D004583:Electrons; D004952:Esters / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
D000577:Amides; D004952:Esters; D010455:Peptides; D011506:Proteins; D012997:Solvents; C011083:polyproline; D011392:Proline