Rajashankar K R, Ramakumar S, Mal T K, Jain R M, Chauhan V S
Department of Physics, Indian Institute of Science, Bangalore.
Biopolymers. 1995 Feb;35(2):141-7. doi: 10.1002/bip.360350202.
alpha,beta-Dehydro amino acid residues are known to constrain the peptide backbone to the beta-bend conformation. A pentapeptide containing only one alpha,beta-dehydrophenylalanine (delta Phe) residue has been synthesized and crystallized, and its solid state conformation has been determined. The pentapeptide Boc-Leu-Phe-Ala-delta Phe-Leu-OMe (C39H55N5O8, Mw = 721.9) was crystallized from aqueous methanol. Monoclinic space group was P2(1), a = 10.290(2) degrees, b = 17.149(2) degrees, c = 12.179(2) A, beta = 96.64(1) degrees with two molecules in the unit cell. The x-ray (MoK alpha, lambda = 0.7107A) intensity data were collected using a CAD4 diffractometer. The crystal structure was determined by direct methods and refined using least-squares technique. R = 4.4% and Rw = 5.4% for 4403 reflections having magnitude of F0 > or = 3 sigma(magnitude of F0). All the peptide links are trans and the pentapeptide molecule assumes 3(10)-helical conformation. The mean phi,psi values, averaged over the first four residues, are -64.4 degrees, -22.4 degrees respectively. There are three 4-->1 intramolecular hydrogen bonds, characteristic of 3(10)-helix. In the crystal, the peptide helices interact through two head-to-tail, N-H-O intermolecular hydrogen bonds. The peptide molecules related by 2(1) screw symmetry form a skewed assembly of helices.
已知α，β-脱氢氨基酸残基可将肽主链限制为β-转角构象。已合成并结晶出一种仅含一个α，β-脱氢苯丙氨酸（δPhe）残基的五肽，并确定了其固态构象。五肽Boc-Leu-Phe-Ala-δPhe-Leu-OMe（C39H55N5O8，Mw = 721.9）从甲醇水溶液中结晶出来。单斜空间群为P2(1)，a = 10.290(2) 埃，b = 17.149(2) 埃，c = 12.179(2) 埃，β = 96.64(1)°，晶胞中有两个分子。使用CAD4衍射仪收集X射线（MoKα，λ = 0.7107埃）强度数据。通过直接法确定晶体结构，并使用最小二乘法进行精修。对于4403个|F0|≥3σ(|F0|)的反射，R = 4.4%，Rw = 5.4%。所有肽键均为反式，五肽分子呈3(10)-螺旋构象。前四个残基的平均φ、ψ值分别为-64.4°、-22.4°。有三个4→1分子内氢键，这是3(10)-螺旋的特征。在晶体中，肽螺旋通过两个头对尾的N-H-O分子间氢键相互作用。由2(1)螺旋对称相关的肽分子形成螺旋的倾斜组装体。
