Skálová Tereza, Dohnálek Jan, Spiwok Vojtech, Lipovová Petra, Vondrácková Eva, Petroková Hana, Dusková Jarmila, Strnad Hynek, Králová Blanka, Hasek Jindrich
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, 1606 Praha 6, Czech Republic.
J Mol Biol. 2005 Oct 21;353(2):282-94. doi: 10.1016/j.jmb.2005.08.028.
The X-ray structure of cold-active beta-galactosidase (isoenzyme C-2-2-1) from an Antarctic bacterium Arthrobacter sp. C2-2 was solved at 1.9A resolution. The enzyme forms 660 kDa hexamers with active sites opened to the central cavity of the hexamer and connected by eight channels with exterior solvent. To our best knowledge, this is the first cold-active beta-galactosidase with known structure and also the first known beta-galactosidase structure in the form of compact hexamers. The hexamer organization regulates access of substrates and ligands to six active sites and this unique packing, present also in solution, raises questions about its purpose and function. This enzyme belongs to glycosyl hydrolase family 2, similarly to Escherichia coli beta-galactosidase, forming tetramers necessary for its enzymatic function. However, we discovered significant differences between these two enzymes affecting the ability of tetramer/hexamer formation and complementation of the active site. This structure reveals new insights into the cold-adaptation mechanisms of enzymatic pathways of extremophiles.
解析出了来自南极节杆菌属细菌Arthrobacter sp. C2-2的冷活性β-半乳糖苷酶(同工酶C-2-2-1)的X射线结构,分辨率为1.9埃。该酶形成660 kDa的六聚体,活性位点向六聚体的中心腔开放,并通过八个通道与外部溶剂相连。据我们所知,这是首个具有已知结构的冷活性β-半乳糖苷酶,也是首个已知的呈紧密六聚体形式的β-半乳糖苷酶结构。六聚体结构调控底物和配体进入六个活性位点,这种独特的堆积方式在溶液中也存在,引发了关于其目的和功能的疑问。该酶与大肠杆菌β-半乳糖苷酶一样,属于糖基水解酶家族2,形成其酶功能所需的四聚体。然而,我们发现这两种酶之间存在显著差异,影响四聚体/六聚体的形成能力以及活性位点的互补性。这一结构揭示了对嗜极生物酶促途径冷适应机制的新见解。