Division of Magnetic Resonance Research, Korea Basic Science Institute, Chungbuk, Korea.
FASEB J. 2012 Jan;26(1):219-28. doi: 10.1096/fj.11-188425. Epub 2011 Sep 30.
The outer membrane protein A (OmpA) plays important roles in anchoring of the outer membrane to the bacterial cell wall. The C-terminal periplasmic domain of OmpA (OmpA-like domain) associates with the peptidoglycan (PGN) layer noncovalently. However, there is a paucity of information on the structural aspects of the mechanism of PGN recognition by OmpA-like domains. To elucidate this molecular recognition process, we solved the high-resolution crystal structure of an OmpA-like domain from Acinetobacter baumannii bound to diaminopimelate (DAP), a unique bacterial amino acid from the PGN. The structure clearly illustrates that two absolutely conserved Asp271 and Arg286 residues are the key to the binding to DAP of PGN. Identification of DAP as the central anchoring site of PGN to OmpA is further supported by isothermal titration calorimetry and a pulldown assay with PGN. An NMR-based computational model for complexation between the PGN and OmpA emerged, and this model is validated by determining the crystal structure in complex with a synthetic PGN fragment. These structural data provide a detailed glimpse of how the anchoring of OmpA to the cell wall of gram-negative bacteria takes place in a DAP-dependent manner.
外膜蛋白 A（OmpA）在外膜与细菌细胞壁的锚定中发挥重要作用。OmpA 的 C 端周质域（OmpA 样结构域）与肽聚糖（PGN）层非共价结合。然而，关于 OmpA 样结构域识别 PGN 的机制的结构方面的信息很少。为了阐明这个分子识别过程，我们解析了鲍曼不动杆菌的 OmpA 样结构域与二氨基庚二酸（DAP）结合的高分辨率晶体结构，DAP 是 PGN 中的一种独特细菌氨基酸。该结构清楚地表明，两个绝对保守的天冬氨酸残基 271 和精氨酸残基 286 是结合 PGN 中 DAP 的关键。DAP 作为 PGN 与 OmpA 中心锚定位点的鉴定，进一步得到了与 PGN 的等温滴定量热法和下拉测定的支持。出现了基于 NMR 的 PGN 与 OmpA 之间复合物形成的计算模型，并且通过确定与合成 PGN 片段的复合物的晶体结构对该模型进行了验证。这些结构数据提供了一个详细的视角，说明 OmpA 如何以 DAP 依赖性的方式锚定在革兰氏阴性菌的细胞壁上。
