Reshaping the Activity–Stability Landscape of a 1,2-Rhamnosyltransferase via Distal Mutational Engineering

Rhamnosyltransferases are remarkable biocatalysts for the synthesis of rhamnosylated natural products with valuable physicochemical properties and bioactivities. However, their application is hindered by poor stability and low catalytic efficiency. Here, we achieved simultaneous enhancement of catalytic efficiency and stability of a 1,2-rhamnosyltransferase by a distal mutational engineering strategy. The variant M9 exhibited a 589.43-fold extension in half-life, a 2.5 °C increase in Tm, a 13.6 °C increase in T50, and an 8- to 763-fold increase in activity toward diverse flavonoids compared with the wild type. Molecular dynamics simulations provided insights into enhanced thermostability and catalytic efficiency. To demonstrate its synthetic utility, a whole-cell biocatalytic system was constructed in E. coli by coexpressing M9 and UDP-rhamnose synthase, enabling a neohesperidin titer of 1.14 g L-1 without exogenous sugar donor supplementation. This study presents a practical enzyme engineering strategy for simultaneous activity-stability enhancement in glycosyltransferases and provides a promising biocatalyst for rhamnosylated natural product biosynthesis.