Ligand-induced Conformational Changes in the Bacillus subtilis Chemoreceptor McpB Determined by Disulfide Crosslinking in vivo

Self Cite

During chemotaxis toward asparagine by Bacillus subtilis, the ligand is thought to bind to the chemoreceptor McpB on the exterior of the cell and induce a conformational change. This change affects the degree of phosphorylation of the CheA kinase bound to the cytoplasmic region of the receptor. Until recently, the sensing domains of the B. subtilis receptors were thought to be structurally similar to the well studied Escherichia coli fourhelical bundle. However, sequence analysis has shown the sensing domains of receptors from these two organisms to be vastly different. Homology modeling of the sensing domain of the B. subtilis asparagine receptor McpB revealed two tandem PAS domains. McpB mutants having alanine substitutions in key arginine and tyrosine residues of the upper PAS domain but not in any residues of the lower PAS domain exhibited a chemotactic defect in both swarm plates and capillary assays. Thus, binding does not appear to occur across any dimeric surface but within a monomer. A modified capillary assay designed to determine the concentration of attractant where chemotaxis is most sensitive showed that when Arg-111, Tyr-121, or Tyr-133 is mutated to an alanine, much more asparagine is required to obtain an active chemoreceptor. Isothermal titration calorimetry experiments on the purified sensing domain showed a K D to asparagine of 14 M, with the three mutations leading to less efficient binding. Taken together, these results reveal not only a novel chemoreceptor sensing domain architecture but also, possibly, a different mechanism for chemoreceptor activation.Many species of bacteria are able to sense their proximal chemical environment and move toward more favorable locations through a process known as chemotaxis. At the heart of all known bacterial chemotaxis pathways is a two-component signal transduction system involving the CheA histidine kinase and the CheY response regulator. In the Gram-positive bacterium Bacillus subtilis, the CheA kinase forms a stable complex with the chemotaxis receptors, also known as methyl-accepting chemotaxis proteins (MCPs), and the CheW and CheV adaptor proteins (1). When the receptors sense attractant molecules, they enhance the rate of CheA autophosphorylation, which in turn causes CheY-P concentrations to increase (2-4). In B. subtilis, the binding of CheY-P to the cytoplasmic face of the flagellum increases the likelihood of smooth runs (5). By biasing the duration and frequency of run and tumble swimming events, the bacterium is able to migrate up gradients of attractant molecules. In addition to this core signal transduction module, the B. subtilis pathway also possesses two CheY-P phosphatases and a number of regulatory proteins involved in sensory adaptation (6, 7). One of the remarkable features of the chemotaxis system is its ability to adapt the bacteria to their surrounding environment so that relative changes in the chemical concentrations can be sensitively detected.The chemotaxis receptors have previously been shown to be long, ␣-helical homodime...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

A PAS Domain Binds Asparagine in the Chemotaxis Receptor McpB in Bacillus subtilis

Glekas

Foster

Cates

et al. 2010

Self Cite

“…The binding of an effector molecule to the sensor domain induces sliding and/or rotational movement of the transmembrane four-helix bundle that connects the periplasmic sensor domain with the cytoplasmic signaling domain. This movement is considered to be a key step in the signal transduction mechanism of MCP (39,40). Although HemAT-Bs lacks the transmembrane region, the G-and H-helices of the two subunits form an antiparallel four-helix bundle, as illustrated in Fig.…”

Section: Insights Into Signal Transduction Mechanism Of Hemat-bs-mentioning

confidence: 99%

Site-specific Protein Dynamics in Communication Pathway from Sensor to Signaling Domain of Oxygen Sensor Protein, HemAT-Bs

El-Mashtoly

Kubo

et al. 2012

Background:HemAT is an O 2 sensor and functions as a signal transducer for aerotaxis. Results: The UV resonance Raman spectra indicated two phases of intensity changes for the Trp, Tyr, and Phe bands of proteins. Conclusion: Changes in the heme structure drive displacements of the B-and G-helices upon CO photolysis. Significance: Understanding the communication pathway from the sensor to signaling domain of HemAT-Bs.

“…The conformational changes of G-helix residues are quite important for the signal transduction mechanism of HemAT-Bs, as discussed below. The signal transduction mechanism has been proposed for MCPs, which are membrane-bound proteins (42,43). A pair of two antiparallel helices in a MCP dimer forms a transmembrane four-helix bundle that connects the periplasmic sensor domain and the cytoplasmic signaling domain.…”

Section: Effects Of Mutations Of Thr 95 and His 86 On The O 2 -Inducementioning

confidence: 99%

“…A pair of two antiparallel helices in a MCP dimer forms a transmembrane four-helix bundle that connects the periplasmic sensor domain and the cytoplasmic signaling domain. The binding of the effector molecule to the sensor domain induces a slide and/or rotational movement of this helix bundle, which is a key step in the signal transduction mechanism of MCPs (42,43).…”

Section: Effects Of Mutations Of Thr 95 and His 86 On The O 2 -Inducementioning

confidence: 99%

Protein Conformation Changes of HemAT-Bs upon Ligand Binding Probed by Ultraviolet Resonance Raman Spectroscopy

El-Mashtoly¹,

Yoshimura

et al. 2008