Zagari A, Némethy G, Scheraga H A
Dipartimento di Chimica, Università di Napoli, Italy.
Biopolymers. 1990;30(9-10):951-9. doi: 10.1002/bip.360300909.
The L-azetidine-2-carboxylic acid (Aze) residue can be incorporated into proteins in the place of L-proline, of which it is the lower homologue. This substitution alters the properties of proteins, especially of collagen. Conformational constraints in N-acetyl-Aze-N'-methylamide and in several dipeptides containing Aze have been analyzed by means of energy computations. They have been compared with peptides containing Pro. The overall conformational preferences of Aze and Pro are similar, but several significant differences occur between them. In general, peptides containing Aze are somewhat more flexible than corresponding peptides containing Pro, because of a decrease in constraints caused by repulsive nonconvalent interactions of the atoms of the ring with neighboring residues. This results in an entropic effect that lessens the stability of ordered polypeptide conformations with respect to the disordered statistical coil. The collagen-like near-extended conformation is energetically less favorable for Aze than for Pro in the single residue and in dipeptides. This effect also contributes to a destabilization of the collagen triple helix. The influence of Aze on the conformation of polypeptides is discussed in the accompanying papers.
L-氮杂环丁烷-2-羧酸（Aze）残基可取代L-脯氨酸掺入蛋白质中，Aze是L-脯氨酸的低级同系物。这种取代会改变蛋白质的性质，尤其是胶原蛋白的性质。通过能量计算分析了N-乙酰-Aze-N'-甲酰胺以及几种含Aze的二肽中的构象限制。将它们与含Pro的肽进行了比较。Aze和Pro的总体构象偏好相似，但它们之间存在一些显著差异。一般来说，含Aze的肽比相应的含Pro的肽更具柔性，这是由于环原子与相邻残基之间的排斥性非共价相互作用导致的限制减少。这会产生一种熵效应，相对于无序的统计卷曲，减弱了有序多肽构象的稳定性。在单残基和二肽中，类胶原蛋白的近伸展构象对Aze的能量有利程度低于对Pro的能量有利程度。这种效应也导致胶原蛋白三螺旋的不稳定。Aze对多肽构象的影响在随附论文中进行了讨论。
