Biomedical Program, CSIRO, 343 Royal Parade, Parkville, VIC 3052, Australia.
Health and Biosecurity, CSIRO, Clunies Ross Street, Black Mountain, ACT 2601, Australia.
Acta Crystallogr D Struct Biol. 2019 Jul 1;75(Pt 7):639-646. doi: 10.1107/S2059798319008131. Epub 2019 Jun 26.
The structure of BgaR, a transcriptional regulator of the lactose operon in Clostridium perfringens, has been solved by SAD phasing using a mercury derivative. BgaR is an exquisite sensor of lactose, with a binding affinity in the low-micromolar range. This sensor and regulator has been captured bound to lactose and to lactulose as well as in a nominal apo form, and was compared with AraC, another saccharide-binding transcriptional regulator. It is shown that the saccharides bind in the N-terminal region of a jelly-roll fold, but that part of the saccharide is exposed to bulk solvent. This differs from the classical AraC saccharide-binding site, which is mostly sequestered from the bulk solvent. The structures of BgaR bound to lactose and to lactulose highlight how specific and nonspecific interactions lead to a higher binding affinity of BgaR for lactose compared with lactulose. Moreover, solving multiple structures of BgaR in different space groups, both bound to saccharides and unbound, verified that the dimer interface along a C-terminal helix is similar to the dimer interface observed in AraC.
BgaR 是梭菌属中乳糖操纵子的转录调节剂，其结构已通过使用汞衍生物的 SAD 相位测定法解决。BgaR 是乳糖的精密传感器，具有低微摩尔范围内的结合亲和力。这种传感器和调节剂已被捕获为与乳糖以及乳果糖结合，以及在名义上的无配体形式，并且与另一种糖结合转录调节剂 AraC 进行了比较。结果表明，糖结合在果冻卷折叠的 N 端区域，但糖的一部分暴露于大量溶剂中。这与经典的 AraC 糖结合位点不同，后者主要与大量溶剂隔离。与乳糖和乳果糖结合的 BgaR 的结构突出了特异性和非特异性相互作用如何导致 BgaR 对乳糖的结合亲和力高于乳果糖。此外，通过在不同的空间群中解决多个 BgaR 结构，包括结合和未结合的糖，证实了沿着 C 末端螺旋的二聚体界面与在 AraC 中观察到的二聚体界面相似。
