Urry D W, Walter R
Proc Natl Acad Sci U S A. 1971 May;68(5):956-8. doi: 10.1073/pnas.68.5.956.
A conformation of the neurohypophyseal hormone oxytocin in solution is proposed. The structure possesses, in addition to the beta-turn comprised of the sequence -L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl- in the ring component of the hormonal molecule, a second beta-turn involving the C-terminal oxytocin sequence, -L-cysteinyl-L-prolyl-L-leucylglycinamide. The resulting oxytocin structure places the bulky side chains of the leucine and isoleucine residues, as well as the cyclic moiety of the proline residue, at corners of the two beta-turns. A critical role is played by the asparagine residue: its peptide N-H participates in the formation of the hydrogen-bonded cyclic structure of the beta-turn in the ring component of oxytocin and its peptide C=O can be hydrogen-bonded to the N-H of tyrosine, while its side chain C=O stabilizes the second beta-turn by forming a hydrogen bond with the N-H of the leucine residue, which is part of the end peptide of the second beta-turn. This conformational assignment of oxytocin is consistent with hydrogen-deuterium exchange studies, with plots of temperature dependence of peptide proton chemical shifts, and with the coupling constants for the NH-CH dihedral angles.
本文提出了神经垂体激素催产素在溶液中的一种构象。该结构除了在激素分子的环结构部分含有由-L-酪氨酰-L-异亮氨酰-L-谷氨酰胺基-L-天冬酰胺基序列组成的β-转角外，还存在一个涉及C端催产素序列-L-半胱氨酰-L-脯氨酰-L-亮氨酰甘氨酰胺的第二个β-转角。由此产生的催产素结构将亮氨酸和异亮氨酸残基的庞大侧链以及脯氨酸残基的环状部分置于两个β-转角的转角处。天冬酰胺残基起着关键作用：其肽键N-H参与催产素环结构部分β-转角氢键环结构的形成，其肽键C=O可与酪氨酸的N-H形成氢键，而其侧链C=O通过与亮氨酸残基的N-H形成氢键来稳定第二个β-转角，亮氨酸残基是第二个β-转角末端肽的一部分。催产素的这种构象分配与氢-氘交换研究、肽质子化学位移的温度依赖性图以及NH-CH二面角的耦合常数一致。
