Hinderaker Matthew P, Raines Ronald T
Department of Chemistry and Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Protein Sci. 2003 Jun;12(6):1188-94. doi: 10.1110/ps.0241903.
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.
肽键对反式构象的众所周知的偏好归因于空间效应。在这里，我们表明，带有N-甲酰基（H(i-1)-C'(i-1)=O(i-1)）的脯氨酸残基，其中H(i-1)的空间位阻比O(i-1)小，同样偏好反式构象。因此，肽键对反式构象的偏好不能仅用空间效应来解释。相反，肽键的氧（O(i-1)）与多肽链中随后的羰基碳（C'(i)）之间的n→π相互作用也促成了这种偏好。在聚脯氨酸II螺旋中，O(i-1)和C'(i)的距离以及O(i-1).C'(i)=O(i)角度特别有利于这种n→π相互作用。我们提出，这种电子效应为蛋白质结构的这一元素和其他元素提供了实质性的稳定性。
