Department of Plant Pathology, Shandong Agricultural University, Tai'an, Shandong, China.
PLoS One. 2013 Nov 11;8(11):e80024. doi: 10.1371/journal.pone.0080024. eCollection 2013.
Polyhydroxyalkanoates (PHAs) have attracted increasing attention as "green plastic" due to their biodegradable, biocompatible, thermoplastic, and mechanical properties, and considerable research has been undertaken to develop low cost/high efficiency processes for the production of PHAs. MaoC-like hydratase (MaoC), which belongs to (R)-hydratase involved in linking the β-oxidation and the PHA biosynthetic pathways, has been identified recently. Understanding the regulatory mechanisms of (R)-hydratase catalysis is critical for efficient production of PHAs that promise synthesis an environment-friendly plastic.
METHODOLOGY/PRINCIPAL FINDINGS: We have determined the crystal structure of a new MaoC recognized from Phytophthora capsici. The crystal structure of the enzyme was solved at 2.00 Å resolution. The structure shows that MaoC has a canonical (R)-hydratase fold with an N-domain and a C-domain. Supporting its dimerization observed in structure, MaoC forms a stable homodimer in solution. Mutations that disrupt the dimeric MaoC result in a complete loss of activity toward crotonyl-CoA, indicating that dimerization is required for the enzymatic activity of MaoC. Importantly, structure comparison reveals that a loop unique to MaoC interacts with an α-helix that harbors the catalytic residues of MaoC. Deletion of the loop enhances the enzymatic activity of MaoC, suggesting its inhibitory role in regulating the activity of MaoC.
CONCLUSIONS/SIGNIFICANCE: The data in our study reveal the regulatory mechanism of an (R)-hydratase, providing information on enzyme engineering to produce low cost PHAs.
聚羟基烷酸酯（PHA）因其可生物降解、生物相容、热塑性和机械性能而被作为“绿色塑料”引起了越来越多的关注，并且已经进行了大量研究以开发低成本/高效率的生产 PHA 的工艺。最近已经鉴定出毛 C 样水合酶（MaoC），它属于参与β-氧化和 PHA 生物合成途径的（R）-水合酶。理解（R）-水合酶催化的调控机制对于高效生产 PHA 至关重要，PHA 有望合成一种环保塑料。
方法/主要发现：我们已经从辣椒疫霉中确定了一种新的 MaoC 的晶体结构。该酶的晶体结构在 2.00 Å 分辨率下得到解决。结构表明 MaoC 具有典型的（R）-水合酶折叠结构，具有 N 结构域和 C 结构域。结构中观察到的二聚化支持其在溶液中形成稳定的同源二聚体。破坏二聚体 MaoC 的突变导致对巴豆酰-CoA 的活性完全丧失，表明二聚化对于 MaoC 的酶活性是必需的。重要的是，结构比较表明 MaoC 特有的环与含有 MaoC 催化残基的α-螺旋相互作用。该环的缺失增强了 MaoC 的酶活性，表明其在调节 MaoC 活性中起抑制作用。
结论/意义：我们的研究数据揭示了（R）-水合酶的调控机制，为生产低成本 PHA 的酶工程提供了信息。
