Division of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea.
Mol Microbiol. 2009 May;72(3):699-709. doi: 10.1111/j.1365-2958.2009.06680.x. Epub 2009 Apr 7.
Methionine sulphoxide reductases (Msr) catalyse the reduction of oxidized methionine to methionine. These enzymes are divided into two classes, MsrA and MsrB, according to substrate specificity. Although most MsrA and MsrB exist as separate enzymes, in some bacteria these two enzymes are fused to form a single polypeptide (MsrAB). Here, we report the first crystal structure of MsrAB from Streptococcus pneumoniae (SpMsrAB) at 2.4 A resolution. SpMsrAB consists of an N-terminal MsrA domain, a C-terminal MsrB domain and a linker. The linker is composed of 13 residues and contains one 3(10)-helix and several hydrogen bonds interacting with both MsrA and MsrB domains. Interestingly, our structure includes the MsrB domain complexed with an SHMAEI hexa-peptide that is the N-terminal region of neighbouring MsrA domain. A kinetic analysis showed that the apparent K(m) of SpMsrAB for the R-form-substrate was 20-fold lower than that for the S-form substrate, indicating that the MsrB domain had a much higher affinity for the substrate than the MsrA domain. Our study reveals the first structure of the MsrAB by providing insights into the formation of a disulphide bridge in the MsrB, the structure of the linker region, and the distinct structural nature of active site of each MsrA and MsrB domain.
甲硫氨酸亚砜还原酶（Msr）催化氧化甲硫氨酸还原为甲硫氨酸。这些酶根据底物特异性分为 MsrA 和 MsrB 两类。尽管大多数 MsrA 和 MsrB 作为独立的酶存在，但在一些细菌中，这两种酶融合形成单个多肽（MsrAB）。在这里，我们报告了来自肺炎链球菌（SpMsrAB）的 MsrAB 的首个晶体结构，分辨率为 2.4A。SpMsrAB 由 N 端 MsrA 结构域、C 端 MsrB 结构域和连接子组成。连接子由 13 个残基组成，包含一个 3（10）-螺旋和几个氢键，与 MsrA 和 MsrB 结构域相互作用。有趣的是，我们的结构包含与 SHMAEI 六肽复合的 MsrB 结构域，该六肽是相邻 MsrA 结构域的 N 端区域。动力学分析表明，SpMsrAB 对 R 型底物的表观 K(m) 比 S 型底物低 20 倍，表明 MsrB 结构域对底物的亲和力远高于 MsrA 结构域。我们的研究通过提供对 MsrB 中二硫键形成、连接子区域结构以及每个 MsrA 和 MsrB 结构域活性位点的独特结构性质的深入了解，揭示了 MsrAB 的首个结构。
