Recyclable and efficient isoquercitrin production with whole-cell catalysis of improved GH78 α-L-rhamnosidase by domain truncation strategy

Isoquercitrin of great pharmaceutical value can be transformed from plant-derived rutin by the key enzyme α-L-rhamnosidase. However, the disposable hydrolyzation process and the unsatisfactory properties of α-L-rhamnosidase limit the production of isoquercitrin. In this study, we obtained a mutant of GH78 family RhaB1, RhaB1-ΔN, with improved thermostability and catalytic activity by deleting the domain N. Concretely speaking, the T50 for 30 min and melting temperature (Tm) raised 5.0 °C and 6.2 °C compared with those of RhaB1. Meanwhile, the specific activities were 103 %, 44 %, and 74 % higher than those of the wild type with pNPR, rutin, and naringin as substrates, respectively. With RhaB1-ΔN as a whole-cell catalyst, conversion of isoquercitrin reached 96.6 % within 1.5 h, 8.5 h less than that for free RhaB1. In the 6th recovery, the yield of whole-cell catalyst reached 62.3 % of the maximum, 18.9 times that of the free enzyme (3.3 %). The combined strategies of enzyme modification and whole-cell catalyst helped to realize more recyclable and efficient isoquercitrin production.