We are delighted to welcome Prof. Jhimli Dasgupta from Dept. of Biotechnology, St. Xavier’s college, Kolkata for an insightful talk on “Structural insights into the σ54 -dependent transcription activator FlrC, and its cognate sensor histidine kinase FlrB that regulate flagellar synthesis of Vibrio cholerae” on 23 November 2024, 11:30 am onwards at JIVAN – Centre for Research in Biological Sciences, Ramakrishna Mission Seva Pratisthan.

Speaker: Prof. Jhimli Dasgupta from Dept. of Biotechnology, St. Xavier’s College, Kolkata

Abstract

In Vibrio cholerae, FlrA acts as the ‘master regulator’ of flagellar biosynthesis, and activates σ 54 -dependent transcription of an AAA + ATPase FlrC, together with its cognate sensor histidine kinase FlrB. Phosphorylation of the FlrC by the sensor histidine kinase FlrB is essential for flagellar synthesis. Our structural and other biophysical studies delineated that the AAA + domain of FlrC spontaneously forms heptamer that binds ATP in ‘cis-mediated’ style without any contribution from sensor I motif 285 REDXXYR 291 of the trans protomer, which is commonly observed in the NtrC type AAA + ATPases. Heptamerization, coupled with optimal conformation of Walker A, is essential for efficient ATP binding and hydrolysis by FlrC. Excess c-di-GMP represses ATPase activity of FlrC through destabilization of the heptameric assembly, especially at low concentration of protein. The sensor histidine kinase FlrB contains a N-terminal sensory PAS domain, central histidine kinase phosphortransfer /dimerization domain (DHp) and C- terminal catalytic (CA) domain. We have shown that dimeric PAS domain of FlrB with novel fold forms dimer and binds heme as sensory signal. Heme facilitates ATP binding to CA, and this synergistic binding of heme and ATP triggers conformational signalling in FlrB, leading phosphorylation of FlrC for downstream flagellar gene transcription.