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Directed evolution of glycosyltransferase for enhanced efficiency of avermectin glucosylation

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Abstract

Avermectin, produced by Streptomyces avermitilis, is an active compound protective against nematodes, insects, and mites. However, its potential usage is limited by its low aqueous solubility. The uridine diphosphate (UDP)-glycosyltransferase (BLC) from Bacillus licheniformis synthesizes avermectin glycosides with improved water solubility and in vitro antinematodal activity. However, enzymatic glycosylation of avermectin by BLC is limited due to the low conversion rate of this reaction. Thus, improving BLC enzyme activity is necessary for mass production of avermectin glycosides for field application. In this study, the catalytic activity of BLC toward avermectin was enhanced via directed evolution. Three mutants from the BLC mutant library (R57H, V227A, and D252V) had specific glucosylation activity for avermectin 2.0-, 1.8-, and 1.5-fold higher, respectively, than wild-type BLC. Generation of combined mutations via site-directed mutagenesis led to even further enhancement of activity. The triple mutant, R57H/V227A/D252V, had the highest activity, 2.8-fold higher than that of wild-type BLC. The catalytic efficiencies (Kcat/Km) of the best mutant (R57H/V227A/D252V) toward the substrates avermectin and UDP-glucose were improved by 2.71- and 2.29-fold, respectively, compared to those of wild-type BLC. Structural modeling analysis revealed that the free energy of the mutants was − 1.1 to − 7.1 kcal/mol lower than that of wild-type BLC, which was correlated with their improved activity.

Key points

Directed evolution improved the glucosylation activity of BLC toward avermectin.

Combinatorial site-directed mutagenesis led to further enhanced activity.

The mutants exhibited lower free energy values than wild-type BLC.

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The datasets supporting the conclusions of this article are included within the article and its supplementary information file.

Funding

This study was supported by grants from the National Institute of Forest Science (Project No. FE0702-2016-11-2020) and the KRIBB Research Initiative Program (KGM2112133), Republic of Korea.

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Contributions

WGK conceived and designed research. HYC and HSL performed experiments and analyzed data. KHP conducted structural modeling. JHK contributed reagents, review, and editing. HYC, KHP, and WGK wrote the paper. All authors read and approved the manuscript.

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Correspondence to Won-Gon Kim.

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This article does not contain any studies with human participants or animals performed by any of the authors.

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The authors declare no competing interests.

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Choi, HY., Lim, H.S., Park, KH. et al. Directed evolution of glycosyltransferase for enhanced efficiency of avermectin glucosylation. Appl Microbiol Biotechnol 105, 4599–4607 (2021). https://doi.org/10.1007/s00253-021-11279-x

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  • DOI: https://doi.org/10.1007/s00253-021-11279-x

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