Abstract
AbstractThe Witches' Broom Disease, caused by the hemibiotrophic basidiomycete fungus Moniliophthora perniciosa, drastically reduced the production of cocoa in Brazil. Phytosanitation, chemical control, genetically resistant strains, and biological control still leave flaws in the disease eradication process. Effort has been expended in the elucidation of molecular targets, in particular, the structural components of the fungal cell wall, such as the beta(1,3)‐D‐glucan synthase. This enzyme is essential for the cellular construction of the wall, as it catalyses the formation of beta(1,3)‐D‐glucans. Protein structure homology modeling approaches are able to determine the structure of proteins without performing experimental steps, considering the barriers related to experimental methods for the structural determination of molecular targets. The presence of the conserved catalytic residues in members of the same glycosyltransferase family and overall structural analysis suggests that they catalyze glycosyl transfer reactions by similar mechanisms. Therefore, the objective of this study was to determine the three‐dimensional model of the enzyme beta(1,3)‐D‐glucan synthase of M. perniciosa by homology modeling. Both procedures were performed to build the models: a comparative modeling by satisfaction of spatial restraints in MODELLER and a modeling by assembly of rigid bodies in the SWISS‐MODEL software. The models were elected based on analysis of the stereochemistry quality and a quantitative assessment of similarity from the obtained models and to templates. A reasonable structural model was obtained of the beta(1,3)‐D‐glucan synthase enzyme (BegS1). The BegS1 model showed two distinct α/β domains, features of the inverting glycosyltransferase family, and the topology of the folded structure showed 7 beta‐strands and 13 alpha‐helices. The BegS1 model showed the presence of a catalytic cavity formed by the conserved aspartic acid residues (Asp326, 345, 353, and 354 DDxD motif) implicated in substrate binding and/or catalysis. In the BegS1 model, this cavity is near a loop region, as was observed in the GT‐2 family structure. It is encouraging to find that the model for BegS1 agrees well with structures from the GT‐2 enzyme family. © 2012 Wiley Periodicals, Inc.
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