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Functional analysis of the bigR operon from Xylella fastidiosa: identification of inhibitor molecules for the sulfur dioxygenase Blh and possible redox mechanism involved in BigR oxidation and operon activatio

Grant number: 13/24043-0
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): March 01, 2014
Effective date (End): February 28, 2018
Field of knowledge:Biological Sciences - Biochemistry - Molecular Biology
Principal researcher:Celso Eduardo Benedetti
Grantee:Nayara Patricia Vieira de Lira
Home Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Ministério da Ciência, Tecnologia e Inovações (Brasil). Campinas , SP, Brazil
Associated research grant:11/20468-1 - Molecular mechanisms involved in pathogen adaptation and virulence, host resistance and symptom development in citrus-bacteria interactions, AP.TEM


Xylella fastidiosa, the causal agent of Citrus Variegated Chlorosis (CVC), and other bacterial pathogens like Agrobacterium tumefaciens, colonizes the vascular tissues of host plants, where the oxygen concentration is limited. Because these pathogens are strict aerobic organism, they cannot survive in the absence of oxygen. To avoid growth inhibition by hypoxia, these pathogens utilize the bigR operon to eliminate hydrogen sulfide (H2S), a potent inhibitor of cytochrome C oxidase that accumulates inside the cells when oxygen levels are low. Thus, the bigR operon is critical for bacterial growth under low oxygen tension. We found previously that the bigR operon encodes the redox sensor BigR, a repressor protein responsible for the operon regulation, a sulfur dioxygenase and sulfur transferase (Blh) and a sulfite exporter. Blh contains two functional domains, an N-terminal DUF442, which is related to bacterial and mitochondrial rhodaneses, and a C-terminal domain similar to the sulfur dioxygenase ETHE1. In a previous work, the enzymatic activities of the Xylella DUF442 and ETHE1 domains were characterized. However, the structural base for these catalytic mechanisms is still unknown. In addition, the mechanism by which BigR is oxidized in response to hypoxia remains a mystery. In the present study we aim to identify compounds capable of inhibiting the sulfur dioxygenase and rhodanese activities of Blh and test their efficacy against Xylella or Agrobacterium cells under hypoxia. Moreover, we plan to identify possible protein partners of BigR which might help to elucidate the mechanism underlying its redox regulation and operon activation, as well as to investigate possible molecular changes that might occur in the host plant as a result of sulfite accumulation in the xylem vessels.

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