Mechanism of action of cyclic beta-1,2-glucan synthetase from Agrobacterium tumefaciens: competition between cyclization and elongation reactions.

AUTOR(ES)

Williamson, G

RESUMO

We have examined some aspects of the mechanism of cyclic beta-1,2-glucan synthetase from Agrobacterium tumefaciens (235-kDa protein, gene product of the chvB region). The enzyme produces cyclic beta-1,2-glucans containing 17 to 23 glucose residues from UDP-glucose. In the presence of added cyclic beta-1,2-glucans (> 0.5 mg/ml) (containing 17 to 23 glucose residues), the enzyme instead synthesizes larger cyclic beta-1,2-glucans containing 24 to 30 glucose residues. This is achieved by de novo synthesis and not by disproportion reactions with the added product. This is interpreted as inhibition of the specific cyclization reaction for the synthesis of cyclic beta-1,2-glucans containing 17 to 23 glucose residues but with no concomitant effect on the elongation (polymerization) reaction. Temperature and detergents both affect the distribution of sizes of cyclic beta-1,2-glucans, but glucans containing 24 to 30 glucose residues are not produced. We suggest that the size distribution of cyclic beta-1,2-glucan products depends on competing elongation and cyclization reactions.

Documentos Relacionados

• A novel cyclic beta-1,2-glucan mutant of Rhizobium meliloti.
• Osmosensitivity phenotypes of Agrobacterium tumefaciens mutants that lack periplasmic beta-1,2-glucan.
• Role for [corrected] Agrobacterium tumefaciens ChvA protein in export of beta-1,2-glucan.
• Biochemical characterization of avirulent Agrobacterium tumefaciens chvA mutants: synthesis and excretion of beta-(1-2)glucan.
• Molecular Cloning and Characterization of cgs, the Brucella abortus Cyclic β(1-2) Glucan Synthetase Gene: Genetic Complementation of Rhizobium meliloti ndvB and Agrobacterium tumefaciens chvB Mutants