A novel c-di-GMP binding domain in glycosyltransferase BgsA is responsible for the synthesis of a mixed-linkage β-glucan

4 years ago

A novel c-di-GMP binding domain in glycosyltransferase BgsA is responsible for the synthesis of a mixed-linkage β-glucan

Daniela Bertinetti, Daniel Pérez-Mendoza, María-Trinidad Gallegos, Robin Lorenz, Friedrich W. Herberg, Juan Sanjuán

BgsA is the glycosyltransferase (GT) involved in the synthesis of a linear mixed-linkage β-glucan (MLG), a recently described exopolysaccharide activated by c-di-GMP in Sinorhizobium meliloti and other Rhizobiales. Although BgsA displays sequence and structural homology with bacterial cellulose synthases (CS), it does not contain any predictable c-di-GMP binding domain. In this work we demonstrate that the cytoplasmic C-terminal domain of BgsA (C-BgsA) binds c-di-GMP with both high affinity (K_D = 0.23 μM) and specificity. C-BgsA is structurally different to the otherwise equivalent cytoplasmic C-terminal domain of CS, and does not contain PilZ motifs for c-di-GMP recognition. A combination of random and site-directed mutagenesis with surface plasmon resonance (SPR) allowed identification of the C-BgsA residues which are important not only for c-di-GMP binding, but also for BgsA GT activity. The results suggest that the C-BgsA domain is important for both, c-di-GMP binding and GT activity of BgsA. In contrast to bacterial CS where c-di-GMP has been proposed as a derepressor of GT activity, we hypothesize that the C-terminal domain of BgsA plays an active role in BgsA GT activity upon binding c-di-GMP.

Publisher URL: https://www.nature.com/articles/s41598-017-09290-2

DOI: 10.1038/s41598-017-09290-2