Kreusch A, Neubüser A, Schiltz E, Weckesser J, Schulz G E
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.
Protein Sci. 1994 Jan;3(1):58-63. doi: 10.1002/pro.5560030108.
The crystal structure of a membrane channel, homotrimeric porin from Rhodopseudomonas blastica has been determined at 2.0 A resolution by multiple isomorphous replacement and structural refinement. The current model has an R-factor of 16.5% and consists of 289 amino acids, 238 water molecules, and 3 detergent molecules per subunit. The partial protein sequence and subsequently the complete DNA sequence were determined. The general architecture is similar to those of the structurally known porins. As a particular feature there are 3 adjacent binding sites for n-alkyl chains at the molecular 3-fold axis. The side chain arrangement in the channel indicates a transverse electric field across each of the 3 pore eyelets, which may explain the discrimination against nonpolar solutes. Moreover, there are 2 significantly ordered girdles of aromatic residues at the nonpolar/polar borderlines of the interface between protein and membrane. Possibly, these residues shield the polypeptide conformation against adverse membrane fluctuations.
通过多同晶置换和结构精修，已在2.0埃分辨率下测定了来自 Blastica 红假单胞菌的膜通道——同三聚体孔蛋白的晶体结构。当前模型的R因子为16.5%，每个亚基由289个氨基酸、238个水分子和3个去污剂分子组成。测定了部分蛋白质序列，随后测定了完整的DNA序列。总体结构与结构已知的孔蛋白相似。一个特别的特征是在分子三重轴处有3个相邻的正烷基链结合位点。通道中的侧链排列表明在3个孔眼的每一个上都有横向电场，这可能解释了对非极性溶质的区分。此外，在蛋白质与膜界面的非极性/极性边界处有2个明显有序的芳香族残基带。这些残基可能保护多肽构象免受不利的膜波动影响。
