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亮氨酰残基中空间不利侧链构象的观察：L-亮氨酰-L-亮氨酸二甲基亚砜溶剂化物的晶体和分子结构

Observation of a sterically unfavorable side-chain conformation in a leucyl residue: crystal and molecular structure of L-leucyl-L-leucine.DMSO solvate.

作者信息

Mitra S N, Subramanian E

机构信息

Department of Crystallography and Biophysics, University of Madras, India.

出版信息

Biopolymers. 1994 Sep;34(9):1139-43. doi: 10.1002/bip.360340903.

DOI:10.1002/bip.360340903
PMID:7948727
Abstract

The crystal structure of a dipeptide L-leucyl-L-leucine (C12H24N2O3) has been determined. The crystals are monoclinic, space group P2(1), with a = 5.434(4) A, b = 15.712(7) A, c = 11.275(2) A, beta = 100.41(1) degrees, and Z = 2. The crystals contain one molecule of dimethyl sulfoxide (DMSO) as solvent of crystallization for each dipeptide molecule. The structure has been solved by direct methods and refined to a final R index of 0.059 for 920 reflections (sin theta/lambda < or = 0.60 A-1) with I > or = 2 sigma (I). The trans peptide unit shows substantial degree of non-planarity (delta omega = 14 degrees). The peptide backbone adopts an extended conformation with torsion angles of psi 1 = 138(1) degrees, omega 1 = 166(1) degrees, phi 2 = -149.3(7) degrees, psi 21 = 164.2(7) degrees, and psi 22 = -15(1) degrees. For the first leucyl residue, the side-chain conformation is specified by the torsion angles 1 chi 1 = 176.7(7) degrees, 1 chi 21 = 62(1) degrees, 1 chi 22 = -177.4(8) degrees; the second leucyl residue adopts a sterically unfavorable conformation with 2 chi 1 = 61(1) degrees, 2 chi 21 = 97(1) degrees, and 2 chi 22 = -151(1) degrees. The packing involves head-to-tail interaction of peptide molecules and segregation of polar and nonpolar regions. The DMSO molecule is strongly hydrogen bonded to the terminal NH3+ group.

摘要

已确定二肽L-亮氨酰-L-亮氨酸（C12H24N2O3）的晶体结构。晶体为单斜晶系，空间群P2(1)，a = 5.434(4) Å，b = 15.712(7) Å，c = 11.275(2) Å，β = 100.41(1)°，Z = 2。每个二肽分子的晶体中含有一个作为结晶溶剂的二甲基亚砜（DMSO）分子。该结构通过直接法解析，并对920个反射（sin θ/λ ≤ 0.60 Å-1，I ≥ 2σ(I)）进行精修，最终R指数为0.059。反式肽单元显示出相当程度的非平面性（δω = 14°）。肽主链呈伸展构象，扭转角为ψ1 = 138(1)°，ω1 = 166(1)°，φ2 = -149.3(7)°，ψ21 = 164.2(7)°，ψ22 = -15(1)°。对于第一个亮氨酰残基，侧链构象由扭转角1χ1 = 176.7(7)°，1χ21 = 62(1)°，1χ22 = -177.4(8)°确定；第二个亮氨酰残基采用空间不利构象，2χ = 61(1)°，2χ21 = 97(1)°，2χ22 = -151(1)°。堆积涉及肽分子的头对尾相互作用以及极性和非极性区域的分离。DMSO分子与末端NH3+基团形成强氢键。

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