Mowbray S L, Petsko G A
J Biol Chem. 1983 Jul 10;258(13):7991-7. doi: 10.2210/pdb1gbp/pdb.
The x-ray structure of the periplasmic galactose binding protein from Salmonella typhimurium, the specific receptor for taxis toward, and high-affinity transport of, galactose has been solved at 3.0-A resolution using multiple isomorphous replacement. The path of the polypeptide chain has been traced, and a model structure consisting of 292 amino acids has been fit to the electron density map. The overall shape of the molecule is that of a prolate ellipsoid, with dimensions 35 X 35 X 65 A. The protein consists of two similar domains of roughly equal size, related by an axis of pseudosymmetry, and separated by a deep cleft about 8 A wide. Each domain has a core of parallel beta sheet surrounded by five alpha helices, built by alternating strands of sheet and helix in a repeating pattern. Approximately 36% of the residues are involved in alpha helices, and 27% in beta sheet. The tertiary structure has been compared to that of the Escherichia coli arabinose binding protein (Gilliland, G.L., and Quiocho, F. A. (1981) J. Mol. Biol. 146, 341-362), a periplasmic receptor which is involved in transport, but not in chemotaxis. The overall folding of these two molecules is very similar, with the exception of two areas on the surface of the molecule on the long sides of the prolate ellipsoid. The observed variations are adequate to explain the differences in interaction of L-arabinose binding protein and galactose binding protein with the membrane proteins for transport and chemotaxis.
鼠伤寒沙门氏菌周质半乳糖结合蛋白的X射线结构已通过多同晶置换法在3.0埃分辨率下解析出来。该蛋白是半乳糖趋化作用的特异性受体及半乳糖的高亲和力转运蛋白。多肽链的路径已被追踪，由292个氨基酸组成的模型结构已与电子密度图拟合。分子的整体形状为长椭圆形，尺寸为35×35×65埃。该蛋白由两个大小大致相等的相似结构域组成，通过假对称轴对称相关，并由一个约8埃宽的深裂缝隔开。每个结构域都有一个由平行β折叠片层组成的核心，周围环绕着五个α螺旋，由片层和螺旋的交替链以重复模式构建而成。大约36%的残基参与α螺旋，27%参与β折叠片层。已将其三级结构与大肠杆菌阿拉伯糖结合蛋白（吉利兰，G.L.，和基奥乔，F.A.（1981年）《分子生物学杂志》146卷，341 - 362页）的结构进行了比较，后者是一种参与转运但不参与趋化作用的周质受体。这两个分子的整体折叠非常相似，除了长椭圆形分子长边上的两个表面区域。观察到的差异足以解释L -阿拉伯糖结合蛋白和半乳糖结合蛋白与参与转运和趋化作用的膜蛋白相互作用的差异。
