Kreusch A, Schulz G E
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.
J Mol Biol. 1994 Nov 11;243(5):891-905. doi: 10.1006/jmbi.1994.1690.
The structure of the membrane channel porin from the phototrophic bacteria Rhodopseudomonas blastica has been refined at 1.96 A resolution yielding an R-factor of 17.6%. The final model consists of all 289 amino acid residues, 247 water molecules and three detergent molecules modelled as n-octyltetraoxyethylene. One of these detergent molecules binds together with its two symmetry-related molecules tightly in a pocket at the molecular 3-fold axis. This pocket may bind three alkyl chains of a lipopolysaccharide which in turn would stabilize the trimer and could possibly play a role in membrane insertion. The overall shape of this porin resembles OmpF of Escherichia coli more than the only known sequence-related porin from Rhodobacter capsulatus. The membrane contacting surface is similar in all structurally known porins; it shows exceptional frequencies of amino acid residues and side-chain rotamers. The 46-residue loop beta 5-beta 6 of the porin is shown to be tightly fastened to the beta-barrel, excluding an in vivo loop movement that closes the pore. The trimer interface region has the structure of a water-soluble protein with an extensive non-polar core and numerous hydrogen bonds at the surface. The loops at the external end of the barrel are long and rigid whereas those at the periplasmic barrel end are short and mobile. The crystal packing is discussed.
光合细菌 Blastica 红假单胞菌膜通道孔蛋白的结构已在 1.96 Å 分辨率下得到优化，R 因子为 17.6%。最终模型包含所有 289 个氨基酸残基、247 个水分子和三个模拟为正辛基四氧乙烯的去污剂分子。其中一个去污剂分子与其两个对称相关分子在分子三重轴处的一个口袋中紧密结合。这个口袋可能结合脂多糖的三条烷基链，进而稳定三聚体，并可能在膜插入中发挥作用。这种孔蛋白的整体形状与大肠杆菌的 OmpF 更相似，而不是来自荚膜红细菌的唯一已知序列相关孔蛋白。在所有已知结构的孔蛋白中，与膜接触的表面相似；它显示出氨基酸残基和侧链旋转异构体的特殊频率。孔蛋白的 46 个残基的β5-β6 环被证明与β桶紧密相连，排除了在体内使孔关闭的环运动。三聚体界面区域具有水溶性蛋白质的结构，有一个广泛的非极性核心，表面有许多氢键。桶外部末端的环长且刚性，而周质桶末端的环短且可移动。讨论了晶体堆积情况。
