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Abstract Sensory adaptation in bacterial chemotaxis is mediated by posttranslational modifications of methyl‐accepting chemotaxis proteins (MCPs). InEscherichia coli, the adaptation proteins CheR and CheB tether to a conserved C‐terminal receptor pentapeptide. Here,we investigated the function of the pentapeptide motif (N/D)WE(E/N)F inSinorhizobium melilotichemotaxis. Isothermal titration calorimetry revealed stronger affinity of the pentapeptides to CheR and activated CheB relative to unmodified CheB. Strains with mutations of the conserved tryptophan in one or all four MCP pentapeptides resulted in a significant decrease or loss of chemotaxis to glycine betaine, lysine, and acetate, chemoattractants sensed by pentapeptide‐bearing McpX and pentapeptide‐lacking McpU and McpV, respectively. Importantly, we discovered that the pentapeptide mediates chemotaxis when fused to the C‐terminus of pentapeptide‐lacking chemoreceptors via a flexible linker. We propose that adaptational assistance and a threshold number of available sites enable the efficient docking of adaptation proteins to the chemosensory array. Altogether, these results demonstrate thatS. melilotieffectively utilizes a pentapeptide‐dependent adaptation system with a minimal number of tethering units to assist pentapeptide‐lacking chemoreceptors and hypothesize that the higher abundance of CheR and CheB inS. meliloticompared toE. coliallows for ample recruitment of adaptation proteins to the chemosensory array.
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The structural analysis of the periplasmic domain of Sinorhizobium meliloti chemoreceptor McpZ reveals a novel fold and suggests a complex mechanism of transmembrane signaling
Abstract Chemotaxis is a fundamental process whereby bacteria seek out nutrient sources and avoid harmful chemicals. For the symbiotic soil bacteriumSinorhizobium meliloti, the chemotaxis system also plays an essential role in the interaction with its legume host. The chemotactic signaling cascade is initiated through interactions of an attractant or repellent compound with chemoreceptors or methyl‐accepting chemotaxis proteins (MCPs).S. melilotipossesses eight chemoreceptors to mediate chemotaxis. Six of these receptors are transmembrane proteins with periplasmic ligand‐binding domains (LBDs). The specific functions of McpW and McpZ are still unknown. Here, we report the crystal structure of the periplasmic domain of McpZ (McpZPD) at 2.7 Å resolution. McpZPD assumes a novel fold consisting of three concatenated four‐helix bundle modules. Through phylogenetic analyses, we discovered that this helical tri‐modular domain fold arose within the Rhizobiaceae family and is still evolving rapidly. The structure, offering a rare view of a ligand‐free dimeric MCP‐LBD, reveals a novel dimerization interface. Molecular dynamics calculations suggest ligand binding will induce conformational changes that result in large horizontal helix movements within the membrane‐proximal domains of the McpZPD dimer that are accompanied by a 5 Å vertical shift of the terminal helix toward the inner cell membrane. These results suggest a mechanism of transmembrane signaling for this family of MCPs that entails both piston‐type and scissoring movements. The predicted movements terminate in a conformation that closely mirrors those observed in related ligand‐bound MCP‐LBDs.
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- Award ID(s):
- 2128232
- PAR ID:
- 10442161
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Proteins: Structure, Function, and Bioinformatics
- Volume:
- 91
- Issue:
- 10
- ISSN:
- 0887-3585
- Page Range / eLocation ID:
- p. 1394-1406
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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