Dataset Information

Functional mapping of Brucella abortus cyclic beta-1,2-glucan synthase: identification of the protein domain required for cyclization.

ABSTRACT: Cyclic beta-1,2-glucans (CbetaG) are periplasmic homopolysaccharides that have been shown to play an important role in several symbiotic and pathogenic relationships. Cyclic beta-1,2-glucan synthase (Cgs), the enzyme responsible for the synthesis of CbetaG, is an integral membrane polyfunctional protein that catalyzes the four enzymatic activities (initiation, elongation, phosphorolysis, and cyclization) required for the synthesis of CbetaG. Recently, we have identified the glycosyltransferase and the beta-1,2-glucooligosaccharide phosphorylase domains of Brucella abortus Cgs. In this study, we performed large-scale linker-scanning mutagenesis to gain further insight into the functional domains of Cgs. This analysis allowed us to construct a functional map of the enzyme and led to the identification of the minimal region required for the catalysis of initiation and elongation reactions. In addition, we identified the Cgs region (residues 991 to 1544) as being the protein domain required for cyclization and demonstrated that upon cyclization and releasing of the CbetaG, one or more glucose residues remain attached to the protein intermediate that serves as a primer for the next round of CbetaG synthesis. Finally, our results indicate that the overall control of the degree of polymerization of CbetaG is the result of a balance between elongation, phosphorolysis, and cyclization reactions.

SUBMITTER: Guidolin LS

PROVIDER: S-EPMC2631987 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Functional mapping of Brucella abortus cyclic beta-1,2-glucan synthase: identification of the protein domain required for cyclization.

Guidolin L Soledad LS Ciocchini Andrés E AE Iñón de Iannino Nora N Ugalde Rodolfo A RA

Journal of bacteriology 20081212 4

Cyclic beta-1,2-glucans (CbetaG) are periplasmic homopolysaccharides that have been shown to play an important role in several symbiotic and pathogenic relationships. Cyclic beta-1,2-glucan synthase (Cgs), the enzyme responsible for the synthesis of CbetaG, is an integral membrane polyfunctional protein that catalyzes the four enzymatic activities (initiation, elongation, phosphorolysis, and cyclization) required for the synthesis of CbetaG. Recently, we have identified the glycosyltransferase a ...[more]

PMID: 19074375

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Project description:UnlabelledCyclic ?-1,2-glucans (C?G) are periplasmic homopolysaccharides that play an important role in the virulence and interaction of Brucella with the host. Once synthesized in the cytoplasm by the C?G synthase (Cgs), C?G are transported to the periplasm by the C?G transporter (Cgt) and succinylated by the C?G modifier enzyme (Cgm). Here, we used a bacterial two-hybrid system and coimmunoprecipitation techniques to study the interaction network between these three integral inner membrane proteins. Our results indicate that Cgs, Cgt, and Cgm can form both homotypic and heterotypic interactions. Analyses carried out with Cgs mutants revealed that the N-terminal region of the protein (Cgs region 1 to 418) is required to sustain the interactions with Cgt and Cgm as well as with itself. We demonstrated by single-cell fluorescence analysis that in Brucella, Cgs and Cgt are focally distributed in the membrane, particularly at the cell poles, whereas Cgm is mostly distributed throughout the membrane with a slight accumulation at the poles colocalizing with the other partners. In summary, our results demonstrate that Cgs, Cgt, and Cgm form a membrane-associated biosynthetic complex. We propose that the formation of a membrane complex could serve as a mechanism to ensure the fidelity of C?G biosynthesis by coordinating their synthesis with the transport and modification.ImportanceIn this study, we analyzed the interaction and localization of the proteins involved in the synthesis, transport, and modification of Brucella abortus cyclic ?-1,2-glucans (C?G), which play an important role in the virulence and interaction of Brucella with the host. We demonstrate that these proteins interact, forming a complex located mainly at the cell poles; this is the first experimental evidence of the existence of a multienzymatic complex involved in the metabolism of osmoregulated periplasmic glucans in bacteria and argues for another example of pole differentiation in Brucella. We propose that the formation of this membrane complex could serve as a mechanism to ensure the fidelity of C?G biosynthesis by coordinating synthesis with the transport and modification.

Dataset Information

Functional mapping of Brucella abortus cyclic beta-1,2-glucan synthase: identification of the protein domain required for cyclization.

Publications

Functional mapping of Brucella abortus cyclic beta-1,2-glucan synthase: identification of the protein domain required for cyclization.

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