Structural Characterization Of Microcystin Biosynthesis Protein McyF From Microcystis Aeruginosa PCC7806and Juvenile Hormone Epoxide Hydrolase From The Silkworm Bombyx Mori

Water blooms of cyanobacteria represent a worldwide challenge due to their production of a range of neurotoxins. The microcystins are a type of toxins produced by a diverse range of cyanobacteria, including species of the genera Microcystis, Anabaena, Nostoc and Oscillatoria. The biosynthesis of microcystin is completed sequentially by a series of proteins, which are encoded by genes in the same gene cluster. Here we report the crystal structures of the microcystin biosynthesis protein McyF compexed with its substrates L-aspartate, D-aspartae and inhibitor citric acid, respectively. Comparative structural analyses reveal insights into the details of active-site pocket. These findings increase our understanding of the substrate recognition and catalysis of aspartate racemase and might help the exploration of biological methods to inhibit the microcystin synthesis.The juvenile hormone (JH) epoxide hydrolase (JHEH) catalyzes the degradation of JH, which regulates the metamorphosis development of insects. Here we report the2.30A crystal structure of JHEH from the silkworm Bombyx mori (BmJHEH). The overall structure of BmJHEH is composed of an N-terminal segment followed by a core hydrolase domain, which is interrupted by an all-a lid domain. Structural analyses together with molecular simulation reveal insights into the conservation and specificity of the active-site pocket. These findings increase our understanding of the substrate recognition and catalysis of the microsomal epoxide hydrolase family and might help the design of JH-derived pesticides.Bombyx mori silk is one of the most incredible substances in nature. It is a giant complex which is mainly composed of fibroin and sericin. After synthesisin and secretion from the silkgland cells, the silk proteins are subjected to assembling in the silkgland cavity and then spinned as silk. However, the precise assembly process remains mysterious, as well as its complex structure after decades of efforts. As one of the silk component, fibroin is assembled by heavy chain, light chain and glycosylated P25at a certain ratio. Using the tandem expression method, we obtained the soluble complex composed of light chain and C-terminal of heavy chain (FibL-FibHc complex). By using circular dichroism spectra and dynamic light scattering, we found that FibL-FibHc complex forms a stable dimer in solution. Moreover, its secondary structure exhibits similar state in the solution with different pH values, which differs from the N-terminal domain of heavy chain. These preliminary results provide us a basis for further investigation of the structure and assembly of the silk.