Structural and functional characterization of FleQ, a transcriptional factor related to flagellar gene expression and biofilm formation

Author(s)

Bruno Yasui Matsuyama

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT)
• Defense date: 2016-03-11

Examining board members

Marcos Vicente de Albuquerque Salles Navarro; Marcio Vinícius Bertacine Dias; Maria Teresa Marques Nôvo; Flávio Henrique da Silva; Lucile Maria Floeter Winter

• Advisor: Marcos Vicente de Albuquerque Salles Navarro

Abstract

Bacteria can form sessile communities known as biofilm, which has a major industrial impact, causing tubing obstruction and corrosion, and in the health, due to its resistance against antibiotic treatment. In recent years, a novel secondary messenger molecule named c-di-GMP has been discovered as a key regulator in signaling pathways related to the bacteria capacity to alternate between two distinct phenotypes: free-swimming cells and biofilm community. One of the molecular targets of c-di-GMP so far identified is FleQ, a bacterial enhancer binding protein (bEBP), which regulates flagellar gene expression in a σ54 dependent mechanism. FleQ acts also controlling transcription of genes involved in PEL exopolysaccharide synthesis, main component of the protective matrix, possibly in a σ70 dependent process. FleQ activity is regulated by a second protein, FleN, which directly interacts with FleQ. Although the role of FleQ:FleN complex in regulating pel operon has been studied, its effect in flagellar gene transcription has not. For a better understanding of FleQ regulatory mechanism, we obtained the crystallographic structure of the REC domain and the AAA+ domain in its apo state and bound to ADP, ATPγS and c-di-GMP. It has also been identified and confirmed c-di-GMP binding site, the distinct oligomers of FleQ, and also proposed a mechanism by which FleN regulates FleQ. These results suggest an unique mechanism in the transcription mediated by an unusual bEBP that acts in conjunction with both σ54 and σ70 factors, in which oligomerization of FleQ:FleN complex has a crucial role in the regulation of flagellar and biofilm formation genes. These studies also lead to the hypothesis that others bEBP, related to distinct phenotypes, may be regulated by c-di-GMP. (AU)

• FAPESP's process: 11/24168-2 - Structural and functional characterization of FleQ from Pseudomonas and Xanthomonas: a main transcriptional factor responsible for flagellar gene expression and biofilm formation
• Grantee: Bruno Yasui Matsuyama
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)