6yue
Fragment of nitrate/nitrite sensor histidine kinase NarQ (R50S variant)
Structural highlights
FunctionNARQ_ECOLI Acts as a sensor for nitrate/nitrite and transduces signal of nitrate/nitrite availability to the NarL/NarP proteins. NarQ probably activates NarL and NarP by phosphorylation. NarQ probably negatively regulates the NarL protein by dephosphorylation. Publication Abstract from PubMedMembrane-embedded sensor histidine kinases (HKs) and chemoreceptors are used ubiquitously by bacteria and archaea to percept the environment, and are often crucial for their survival and pathogenicity. The proteins can transmit the signal from the sensor domain to the catalytic kinase domain reliably over the span of several hundreds of angstroms, and regulate the activity of the cognate response regulator proteins, with which they form two-component signaling systems (TCSs). Several mechanisms of transmembrane signal transduction in TCS receptors have been proposed, dubbed (swinging) piston, helical rotation, and diagonal scissoring. Yet, despite decades of studies, there is no consensus on whether these mechanisms are common for all TCS receptors. Here, we extend our previous work on Escherichia coli nitrate/nitrite sensor kinase NarQ. We determined a crystallographic structure of the sensor-TM-HAMP fragment of the R50S mutant, which, unexpectedly, was found in a ligand-bound-like conformation, despite an inability to bind nitrate. Subsequently, we reanalyzed the structures of the ligand-free and ligand-bound NarQ and NarX sensor domains, and conducted extensive molecular dynamics simulations of ligand-free and ligand-bound wild type and mutated NarQ. Based on the data, we show that binding of nitrate to NarQ causes, first and foremost, helical rotation and diagonal scissoring of the alpha-helices at the core of the sensor domain. These conformational changes are accompanied by a subtle piston-like motion, which is amplified by a switch in the secondary structure of the linker between the sensor and TM domains. We conclude that helical rotation, diagonal scissoring, and piston are simply different degrees of freedom in coiled-coil proteins and are not mutually exclusive in NarQ, and likely in other nitrate sensors and TCS proteins as well. Sensor Histidine Kinase NarQ Activates via Helical Rotation, Diagonal Scissoring, and Eventually Piston-Like Shifts.,Gushchin I, Orekhov P, Melnikov I, Polovinkin V, Yuzhakova A, Gordeliy V Int J Mol Sci. 2020 Apr 28;21(9). pii: ijms21093110. doi: 10.3390/ijms21093110. PMID:32354084[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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