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

ABSTRACT: BgsA is the glycosyltransferase (GT) involved in the synthesis of a linear mixed-linkage ?-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 (KD?=?0.23??M) 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.

SUBMITTER: Perez-Mendoza D 

PROVIDER: S-EPMC5567048 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature