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Molecular mechanisms associated with xylan degradation by Xanthomonas plant pathogens.

ABSTRACT: Xanthomonas pathogens attack a variety of economically relevant plants, and their xylan CUT system (carbohydrate utilization with TonB-dependent outer membrane transporter system) contains two major xylanase-related genes, xynA and xynB, which influence biofilm formation and virulence by molecular mechanisms that are still elusive. Herein, we demonstrated that XynA is a rare reducing end xylose-releasing exo-oligoxylanase and not an endo-?-1,4-xylanase as predicted. Structural analysis revealed that an insertion in the ?7-?7 loop induces dimerization and promotes a physical barrier at the +2 subsite conferring this unique mode of action within the GH10 family. A single mutation that impaired dimerization became XynA active against xylan, and high endolytic activity was achieved when this loop was tailored to match a canonical sequence of endo-?-1,4-xylanases, supporting our mechanistic model. On the other hand, the divergent XynB proved to be a classical endo-?-1,4-xylanase, despite the low sequence similarity to characterized GH10 xylanases. Interestingly, this enzyme contains a calcium ion bound nearby to the glycone-binding region, which is required for catalytic activity and structural stability. These results shed light on the molecular basis for xylan degradation by Xanthomonas and suggest how these enzymes synergistically assist infection and pathogenesis. Our findings indicate that XynB contributes to breach the plant cell wall barrier, providing nutrients and facilitating the translocation of effector molecules, whereas the exo-oligoxylanase XynA possibly participates in the suppression of oligosaccharide-induced immune responses.

SUBMITTER: Santos CR

PROVIDER: S-EPMC4231694 | biostudies-literature | 2014 Nov

REPOSITORIES: biostudies-literature

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Molecular mechanisms associated with xylan degradation by Xanthomonas plant pathogens.

Santos Camila Ramos CR Hoffmam Zaira Bruna ZB de Matos Martins Vanesa Peixoto VP Zanphorlin Leticia Maria LM de Paula Assis Leandro Henrique LH Honorato Rodrigo Vargas RV Lopes de Oliveira Paulo Sérgio PS Ruller Roberto R Ruller Roberto R Murakami Mario Tyago MT

The Journal of biological chemistry 20140929 46

Xanthomonas pathogens attack a variety of economically relevant plants, and their xylan CUT system (carbohydrate utilization with TonB-dependent outer membrane transporter system) contains two major xylanase-related genes, xynA and xynB, which influence biofilm formation and virulence by molecular mechanisms that are still elusive. Herein, we demonstrated that XynA is a rare reducing end xylose-releasing exo-oligoxylanase and not an endo-β-1,4-xylanase as predicted. Structural analysis revealed ...[more]

PMID: 25266726

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Dataset Information

Molecular mechanisms associated with xylan degradation by Xanthomonas plant pathogens.

Publications

Molecular mechanisms associated with xylan degradation by Xanthomonas plant pathogens.

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