El Ghachi Meriem, Howe Nicole, Huang Chia-Ying, Olieric Vincent, Warshamanage Rangana, Touzé Thierry, Weichert Dietmar, Stansfeld Phillip J, Wang Meitian, Kerff Fred, Caffrey Martin
Centre d'Ingénierie des Protéines, InBioS, Université de Liège, allée du 6 Août 19, Bât B5a, 4000, Liège, Belgium.
Membrane Structural and Functional Biology (MS&FB) Group, School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, Dublin 2, D02 R590, Ireland.
Nat Commun. 2018 Mar 14;9(1):1078. doi: 10.1038/s41467-018-03477-5.
As a protective envelope surrounding the bacterial cell, the peptidoglycan sacculus is a site of vulnerability and an antibiotic target. Peptidoglycan components, assembled in the cytoplasm, are shuttled across the membrane in a cycle that uses undecaprenyl-phosphate. A product of peptidoglycan synthesis, undecaprenyl-pyrophosphate, is converted to undecaprenyl-phosphate for reuse in the cycle by the membrane integral pyrophosphatase, BacA. To understand how BacA functions, we determine its crystal structure at 2.6 Å resolution. The enzyme is open to the periplasm and to the periplasmic leaflet via a pocket that extends into the membrane. Conserved residues map to the pocket where pyrophosphorolysis occurs. BacA incorporates an interdigitated inverted topology repeat, a topology type thus far only reported in transporters and channels. This unique topology raises issues regarding the ancestry of BacA, the possibility that BacA has alternate active sites on either side of the membrane and its possible function as a flippase.
作为围绕细菌细胞的保护性包膜，肽聚糖囊是一个易受攻击的部位和抗生素靶点。在细胞质中组装的肽聚糖成分，通过使用十一异戊二烯磷酸的循环穿梭穿过膜。肽聚糖合成的产物十一异戊二烯焦磷酸，被膜整合焦磷酸酶BacA转化为十一异戊二烯磷酸，以便在循环中重新使用。为了了解BacA的功能，我们确定了其2.6埃分辨率的晶体结构。该酶通过延伸到膜中的口袋向周质和周质小叶开放。保守残基定位到发生焦磷酸解的口袋处。BacA包含一个相互交错的反向拓扑重复序列，这种拓扑类型迄今为止仅在转运蛋白和通道中报道过。这种独特的拓扑结构引发了关于BacA的起源、BacA在膜两侧可能存在交替活性位点的可能性以及其作为翻转酶的可能功能等问题。
