Kennedy Robert J, Tsang Kwok-Yin, Kemp Daniel S
Department of Chemistry, Room 18-582, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Am Chem Soc. 2002 Feb 13;124(6):934-44. doi: 10.1021/ja016285c.
The helicity reporting parameters t/c and theta have been measured at 2, 25, and 60 degrees C in water for the solubilized polyalanine series Ac-Hel-A(n)-(t)LInp(2)K(4)W-NH(2) of length 4 < or = n < or = 14 that bears the helix-initiating and monitoring N-cap Ac-Hel and the spaced solubilizer (t)LInp(2)K(4)W-NH(2) as a C-cap. Correlation of t/c with length shows that the helical propensity for n < or = 6 is ca. 1.0, consistent with our early reports, but that a dramatic increase in temperature dependence and helical propensity occurs for n > or = 8. A model based on hydrogen-bonding cooperativity is proposed to explain this finding, and both t/c and theta are modeled successfully by length-dependent alanine propensities at 2 degrees C of 1.03 for n = 6, 1.15, for 7 < or = n < or = 9 and 1.26 for n > or = 10. The implications of these results for the energetics of helix formation by alanine-rich peptide sequences are discussed.
在2℃、25℃和60℃的水中，对长度为4≤n≤14的可溶性聚丙氨酸系列Ac-Hel-A(n)-(t)LInp(2)K(4)W-NH₂测定了螺旋度报告参数t/c和θ。该系列带有起始螺旋和监测螺旋的N端帽Ac-Hel以及作为C端帽的间隔增溶剂(t)LInp(2)K(4)W-NH₂。t/c与长度的相关性表明，n≤6时的螺旋倾向约为1.0，这与我们早期的报告一致，但对于n≥8，温度依赖性和螺旋倾向会急剧增加。提出了一个基于氢键协同作用的模型来解释这一发现，并且在2℃时，通过长度依赖性丙氨酸倾向成功地对t/c和θ进行了建模，n = 6时为1.03，7≤n≤9时为1.15，n≥10时为1.26。讨论了这些结果对富含丙氨酸的肽序列形成螺旋的能量学的影响。
