Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, India.
PLoS One. 2012;7(7):e41894. doi: 10.1371/journal.pone.0041894. Epub 2012 Jul 26.
An analysis of the Mycobacterium smegmatis genome suggests that it codes for several thiolases and thiolase-like proteins. Thiolases are an important family of enzymes that are involved in fatty acid metabolism. They occur as either dimers or tetramers. Thiolases catalyze the Claisen condensation of two acetyl-Coenzyme A molecules in the synthetic direction and the thiolytic cleavage of 3-ketoacyl-Coenzyme A molecules in the degradative direction. Some of the M. smegmatis genes have been annotated as thiolases of the poorly characterized SCP2-thiolase subfamily. The mammalian SCP2-thiolase consists of an N-terminal thiolase domain followed by an additional C-terminal domain called sterol carrier protein-2 or SCP2. The M. smegmatis protein selected in the present study, referred to here as the thiolase-like protein type 1 (MsTLP1), has been biochemically and structurally characterized. Unlike classical thiolases, MsTLP1 is a monomer in solution. Its structure has been determined at 2.7 Å resolution by the single wavelength anomalous dispersion method. The structure of the protomer confirms that the N-terminal domain has the thiolase fold. An extra C-terminal domain is indeed observed. Interestingly, it consists of six β-strands forming an anti-parallel β-barrel which is completely different from the expected SCP2-fold. Detailed sequence and structural comparisons with thiolases show that the residues known to be essential for catalysis are not conserved in MsTLP1. Consistent with this observation, activity measurements show that MsTLP1 does not catalyze the thiolase reaction. This is the first structural report of a monomeric thiolase-like protein from any organism. These studies show that MsTLP1 belongs to a new group of thiolase related proteins of unknown function.
对耻垢分枝杆菌基因组的分析表明，它编码几种硫解酶和硫解酶样蛋白。硫解酶是参与脂肪酸代谢的重要酶家族。它们以二聚体或四聚体的形式存在。硫解酶催化两分子乙酰辅酶 A 在合成方向上的 Claisen 缩合反应，以及 3-酮酰基辅酶 A 分子在降解方向上的硫解断裂反应。一些耻垢分枝杆菌基因已被注释为特征不明显的 SCP2-硫解酶亚家族的硫解酶。哺乳动物 SCP2-硫解酶由 N 端硫解酶结构域和另外一个称为甾醇载体蛋白-2 或 SCP2 的 C 端结构域组成。本研究中选择的耻垢分枝杆菌蛋白，这里称为硫解酶样蛋白 1 型（MsTLP1），已进行了生化和结构表征。与经典的硫解酶不同，MsTLP1 在溶液中是单体。其结构已通过单波长异常分散法在 2.7 Å 的分辨率下确定。单体的结构证实 N 端结构域具有硫解酶折叠。确实观察到一个额外的 C 端结构域。有趣的是，它由六个β-链组成，形成一个与预期的 SCP2 折叠完全不同的反平行β-桶。与硫解酶的详细序列和结构比较表明，已知对催化至关重要的残基在 MsTLP1 中不保守。与这一观察结果一致，活性测量表明 MsTLP1 不能催化硫解酶反应。这是来自任何生物体的单体硫解酶样蛋白的第一个结构报告。这些研究表明，MsTLP1 属于未知功能的新的硫解酶相关蛋白组。
