RESUMO
In this study, structural analysis was employed to identify three hotspot residues that contribute most to the tetramer formation of a glycoside hydrolase family 2 (GH2) ß-glucuronidase (GUS) from Aspergillus oryzae Li-3. Single-point mutation at these sites completely disrupted the tetramer structure and abolished the glycyrrhizin (GL)-hydrolyzing activity. Then, the W522A dimer was refactored into a tetramer by disulfide bonding, and partial GL activity was restored. Further saturated mutation showed a strong correlation between the GL activity of the mutants and their tetramer ratios. Molecular simulations were employed to illustrate the critical role of the tetramer interface in maintaining a functional active-site structure. The three highly conserved tetramer-forming residues were finally applied to two other GH2 GUSs for tetramer dissociation and demonstrated the significance of the homotetramerization for GL-hydrolyzing activity of GH2 GUSs. This study lays foundation for engineering GL-hydrolyzing GUSs at the quaternary structure level for function regulations.
Assuntos
Glucuronidase , Glicosídeo Hidrolases , Glucuronidase/metabolismo , Glicosídeo Hidrolases/química , Ácido Glicirrízico , Hidrólise , Domínio CatalíticoRESUMO
Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters.