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Structural and biochemical characterization of ligand recognition by CysB, the master regulator of sulfate metabolism

DIR@IMTECH: CSIR-Institute of Microbial Technology

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Title Structural and biochemical characterization of ligand recognition by CysB, the master regulator of sulfate metabolism
 
Creator Mittal, Monica
Singh, Appu Kumar
Kumaran, S.
 
Subject QR Microbiology
 
Description CysB, a member of LysR-type transcriptional regulators, up-regulates the expression of genes associated with sulfate metabolism and cysteine biosynthesis. CysB is activated under sulfur limiting conditions by O-acetylserine (OAS) and N-acetylserine (NAS), but the activation mechanism of CysB remain unknown. Here, we report four crystal structures of ligand binding domains of CysB (CysB-LBD) in apo form and in complex with sulfate, OAS, and NAS. Our results show that CysB has two distinct allosteric ligand binding sites; a sulfate and NAS specific site-1 and a second, NAS and OAS specific site-2. All three ligands bind through the induced-fit mechanism. Surprisingly, OAS remodels the site-1 by binding to site-2, suggesting that site-1 and site-2 are coupled allosterically. Using DNA binding and site-directed mutagenesis approach, we show that OAS enhances NAS mediated activation and mutation at site-1 has no effect on site-2 mediated OAS activation. Results indicate that inducer binding triggered signals from OAS-Specific site-2 are relayed to DBD through site-1. Together, results presented here suggest that induced-fit binding and allosteric coupling between two ligand binding sites and DBD underlie the key feature of CysB activation. Further, this study provides first structural glimpse into recognition of inducer ligands by CysB and provides a general framework to understand how LTTR family regulators respond to dual activators.
 
Publisher Elsevier
 
Date 2017
 
Type Article
PeerReviewed
 
Relation http://dx.doi.org/10.1016/j.biochi.2017.08.011
http://crdd.osdd.net/open/2056/
 
Identifier Mittal, Monica and Singh, Appu Kumar and Kumaran, S. (2017) Structural and biochemical characterization of ligand recognition by CysB, the master regulator of sulfate metabolism. Biochimie, 142. pp. 112-124. ISSN 03009084