Crystal Structure of DmdD, a Crotonase Superfamily Enzyme That Catalyzes the Hydration and Hydrolysis of Methylthioacryloyl-CoA
作者:Dazhi Tan、Warren M. Crabb、William B. Whitman、Liang Tong
DOI:10.1371/journal.pone.0063870
日期:——
Dimethyl-sulphoniopropionate (DMSP) is produced in abundance by marine phytoplankton, and the catabolism of this compound is an important source of carbon and reduced sulfur for marine bacteria and other organisms. The enzyme DmdD catalyzes the last step in the methanethiol (MeSH) pathway of DMSP catabolism. DmdD is a member of the crotonase superfamily of enzymes, and it catalyzes both the hydration and the hydrolysis of methylthioacryloyl-CoA (MTA-CoA), converting it to acetaldehyde, CO2, MeSH, and CoA. We report here the crystal structure of Ruegeria pomeroyi DmdD free enzyme at 1.5 Å resolution and the structures of the E121A mutant in complex with MTA-CoA and 3-methylmercaptopropionate-CoA (MMPA-CoA) at 1.8 Å resolution. DmdD is a hexamer, composed of a dimer of trimers where the three monomers of each trimer are related by a crystallographic 3-fold axis. The overall structure of this hexamer is similar to those of canonical crotonases. However, the C-terminal loops of DmdD in one of the trimers assume a different conformation and contribute to CoA binding in the active site of a neighboring monomer of the trimer, while these loops in the second trimer are disordered. MTA-CoA is bound deep in the active site in the first trimer, but shows a 1.5 Å shift in its position in the second trimer. MMPA-CoA has a similar binding mode to MTA-CoA in the first trimer. MMPA-CoA cannot be hydrated and is only hydrolyzed slowly by DmdD. Replacement of the sulfur atom in MMPA-CoA with a methylene group abolishes hydrolysis, suggesting that the unique property of the substrate is a major determinant of the hydrolysis activity of DmdD.
二甲基硫代丙酸(DMSP)主要由海洋浮游植物产生,这种化合物的分解代谢是海洋细菌和其他生物碳和还原硫的重要来源。酶DmdD催化DMSP分解代谢中甲硫醇(MeSH)途径的最后一步。DmdD是巴豆酶超家族的一员,它催化甲基硫代丙烯酰辅酶A(MTA-CoA)的水化和水解,将其转化为乙醛、二氧化碳、甲硫醇和辅酶A。我们在此报告了鲁氏菌(Ruegeria pomeroyi)DmdD游离酶的晶体结构(1.5 Å分辨率)以及E121A突变体与MTA-CoA和3-甲基硫代丙酸-辅酶A(MMPA-CoA)复合物的结构(1.8 Å分辨率)。DmdD是一种六聚体,由三聚体的二聚体组成,每个三聚体的三个单体通过一个晶体学3倍轴相关。这种六聚体的整体结构与典型的巴豆酶类似。然而,其中一个三聚体中DmdD的C-末端环具有不同的构象,并有助于在相邻三聚体单体的活性位点结合辅酶A,而第二个三聚体中的这些环是无序的。MTA-CoA在第一个三聚体中结合在活性位点的深处,但在第二个三聚体中位置发生了1