Thiolases are CoA-dependent enzymes that catalyze the thiolytic cleavage of 3-ketoacyl-CoA, as well as its reverse reaction, which is the thioester-dependent Claisen condensation reaction. Thiolases are dimers or tetramers (dimers of dimers). All thiolases have two reactive cysteines: ( a) a nucleophilic cysteine, which forms a covalent intermediate, and ( b) an acid/base cysteine. The best characterized thiolase is the Zoogloea ramigera thiolase, which is a bacterial biosynthetic thiolase belonging to the CT-thiolase subfamily. The thiolase active site is also characterized by two oxyanion holes, two active site waters, and four catalytic loops with characteristic amino acid sequence fingerprints. Three thiolase subfamilies can be identified, each characterized by a unique sequence fingerprint for one of their catalytic loops, which causes unique active site properties. Recent insights concerning the thiolase reaction mechanism, as obtained from recent structural studies, as well as from classical and recent enzymological studies, are addressed, and open questions are discussed.

中文翻译：

---

硫解酶：一种利用辅酶 A-硫酯化学来形成和破坏 C-C 键的多功能生物催化剂

硫解酶是 CoA 依赖性酶，可催化 3-酮酰基-CoA 的硫解裂解及其逆反应，即硫酯依赖性克莱森缩合反应。硫解酶是二聚体或四聚体（二聚体的二聚体）。所有硫解酶都具有两个反应性半胱氨酸：(a) 形成共价中间体的亲核半胱氨酸，以及 (b) 酸/碱半胱氨酸。最具特征的硫解酶是Zoogloea ramigera硫解酶，它是一种属于CT-硫解酶亚家族的细菌生物合成硫解酶。硫解酶活性位点的特征还包括两个氧阴离子孔、两个活性位点水和四个具有特征氨基酸序列指纹的催化环。可以鉴定出三个硫解酶亚家族，每个亚家族都以其催化环之一的独特序列指纹为特征，这导致了独特的活性位点特性。讨论了从最近的结构研究以及经典和最近的酶学研究中获得的有关硫解酶反应机制的最新见解，并讨论了悬而未决的问题。