5c71

Publication Abstract from PubMed

Glycoside hydrolases (GHs) have attracted special attention in research aimed at modifying natural products by partial removal of sugar moieties to manipulate their solubility and efficacy. However, these modifications are challenging to control because the low substrate specificity of most GHs often generates undesired by-products. We previously identified a GH2-type fungal beta-glucuronidase from Aspergillus oryzae (PGUS) exhibiting promiscuous substrate specificity in hydrolysis of triterpenoid saponins. Here, we present the PGUS structure, representing the first structure of a fungal beta-glucuronidase, and that of an inactive PGUS mutant in complex with the native substrate glycyrrhetic acid 3-O-mono-beta-glucuronide (GAMG). PGUS displayed a homotetramer structure with each monomer comprising three distinct domains: a sugar-binding, an immunoglobulin-like beta-sandwich, and a TIM barrel domain. Two catalytic residues, Glu(414) and Glu(505), acted as acid/base and nucleophile, respectively. Structural and mutational analyses indicated that the GAMG glycan moiety is recognized by polar interactions with nine residues (Asp(162), His(332), Asp(414), Tyr(469), Tyr(473), Asp(505), Arg(563), Asn(567), and Lys(569)) and that the aglycone moiety is recognized by aromatic stacking and by a pi interaction with the four aromatic residues Tyr(469), Phe(470), Trp(472), and Tyr(473) Finally, structure-guided mutagenesis to precisely manipulate PGUS substrate specificity in the biotransformation of glycyrrhizin into GAMG revealed that two amino acids, Ala(365) and Arg(563), are critical for substrate specificity. Moreover, we obtained several mutants with dramatically improved GAMG yield (>95%). Structural analysis suggested that modulating the interaction of beta-glucuronidase simultaneously toward glycan and aglycone moieties is critical for tuning its substrate specificity toward triterpenoid saponins.

Structure-guided engineering of the substrate specificity of a fungal beta-glucuronidase toward triterpenoid saponins.,Lv B, Sun H, Huang S, Feng X, Jiang T, Li C J Biol Chem. 2018 Jan 12;293(2):433-443. doi: 10.1074/jbc.M117.801910. Epub 2017 , Nov 16. PMID:29146597^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.