Czerminski R, Elber R
Department of Chemistry, University of Illinois, Chicago 60680.
Proc Natl Acad Sci U S A. 1989 Sep;86(18):6963-7. doi: 10.1073/pnas.86.18.6963.
Conformational transitions between the 112 stable states of the tetrapeptide isobutyryl-Ala3-NH-methyl (IAN) are studied theoretically. The objective of the investigation is to advance the understanding of helix formation and of conformational transitions in polypeptides. The possible reaction paths between extended chain and helical configurations are examined in detail. The study of the multiple reaction paths in this 48-atom molecule became possible due to development of a new computational algorithm. It is shown that the helix-coil transitions in IAN follow a sequence of local dihedral flips and that the number of the available routes for the transition is significantly lower than in a random search. A quasi-melting point is obtained at 5 +/- 1 kcal (1 cal = 4.18 J)/mol above the lowest energy minimum. Below this point the molecule is trapped in one or very few minima, and above it the molecule hops between a large number of configurations.
对四肽异丁酰 - Ala3 - NH - 甲基（IAN）的112种稳定状态之间的构象转变进行了理论研究。该研究的目的是增进对多肽中螺旋形成和构象转变的理解。详细研究了伸展链和螺旋构型之间可能的反应路径。由于一种新的计算算法的发展，对这个48原子分子中的多条反应路径进行研究成为可能。结果表明，IAN中的螺旋 - 卷曲转变遵循一系列局部二面角翻转，并且转变的可用路径数量明显低于随机搜索中的数量。在比最低能量最小值高5±1千卡（1卡 = 4.18焦耳）/摩尔处获得了一个准熔点。低于这个点，分子被困在一个或极少数的最小值中，而高于这个点，分子在大量构型之间跳跃。
