Donor specificity of YjiC glycosyltransferase determines the conjugation of cytosolic NDP-sugar in in vivo glycosylation reactions

•Escherichia coli BL21(DE3) mutants were generated by disrupting three different genes to divert carbon flux towards NDP-sugars.•Four different rare dTDP-deoxy-sugars including amino deoxy-sugars were generated in E. coli cytosol.•Flexible glycosyltransferase transferred only l-rhamnose from dTDP-l-rhamnose and tuned to rhamnosyltransferase.•Donor specificity of GT determined the conjugation of cytosolic NDP-sugar in in vivo reactions.

Escherichia coli BL21 (DE3) was engineered by blocking glucose-1-phosphate utilizing glucose phosphate isomerase (pgi), glucose-6-phosphate dehydrogenase (zwf) and uridylyltransferase (galU) genes to produce pool of four different rare dTDP-sugars. The cytosolic pool of dTDP-l-rhamnose, dTDP-d-viosamine, dTDP-4-amino 4,6-dideoxy-d-galactose, and dTDP-3-amino 3,6-dideoxy-d-galactose was generated by overexpressing respective dTDP-sugars biosynthesis genes from various microbial sources. A flexible glycosyltransferase YjiC, from Bacillus licheniformis DSM 13 was also overexpressed to transfer sugar moieties to 3-hydroxyl group of 3-hydroxyflavone, a core unit of flavonoids. Among four rare dTDP-sugars generated in cytosol of engineered strains, YjiC solely transferred l-rhamnose from dTDP-l-rhamnose and tuned to rhamnosyltransferase.