Signaling Consequences of Structural Lesions that Alter the Stability of Chemoreceptor Trimers of Dimers

Abstract

Residues E402 and R404 of the E. coli serine chemoreceptor, Tsr, appear to form a salt bridge that spans the interfaces between neighboring dimers in the Tsr trimer of dimers, a key structural component of receptor core signaling complexes. To assess their functional roles we constructed full sets of single amino acid replacement mutants at E402 and R404 and characterized their signaling behaviors with a suite of in vivo assays. Our results indicate that the E402 and R404 residues of Tsr play their most critical signaling roles at their inner locations near the trimer axis where they likely participate in stabilizing trimer-of-dimer packing and the kinase-ON state of core signaling complexes. Mutant receptors with a variety of sidechain replacements still accessed both the ON and OFF signaling states, suggesting that core signaling complexes produce kinase activity over a range of receptor conformations and dynamic motions. Similarly, the kinase-OFF state may not be a discrete conformation, but rather a range of structures outside the range of those suitable for kinase activation. Consistent with this idea, some structural lesions at both E402 and R404 produced signaling behaviors that are not compatible with discrete two-state models of core complex signaling states. Those lesions might stabilize intermediate receptor conformations along the OFF-ON energy landscape. Amino acid replacements produced different constellations of signaling defects at each residue, indicating that they play distinct structure-function roles. R404, but not E402, was critical for high signal cooperativity in the receptor array.

Class III Histidine Kinases: a Recently Accessorized Kinase Domain in Putative Modulators of Type IV Pilus-Based Motility

“…S6). Interestingly, not only known intradimer contacts, e.g., a conserved phenylalanine corresponding to F396 in Tsr (28), but also some of the contacts critical for the trimer-of-dimer formation, e.g., positions corresponding to E402 and R404 in Tsr (29), are preserved in MCP HKIII (see Fig. S6).…”

Paradoxical enhancement of chemoreceptor detection sensitivity by a sensory adaptation enzyme

“…Structural changes in the receptor's hairpin tip region (Fig. 1) that produce a wide range of signaling behaviors did not potentiate the CheR effect (53)(54)(55). Perhaps the receptor methylation helices, whose conformation and packing stability are under direct control by the HAMP domain, are central to the CheR effect.…”

Effects of Advective-Diffusive Transport of Multiple Chemoattractants on Motility of Engineered Chemosensory Particles in Fluidic Environments

“…We modified the RapidCell (RC) model to simulate chemotactic motility of the ECP with the premise that the ECP mimics E. coli chemotaxis in the presence of two unmixed chemoattractants. The RC model [17] was originally developed to simulate flagellar bacterial chemotaxis in an environment with a spatiotemporally varying concentration gradient of a single chemoattractant, and performs two tasks: chemoattractant signal processing by the methyl-accepting chemotaxis protein (MCP) sensory lattice and adaptive feedback response of the sensory array [16,[23][24][25]. Signal processing by the cell occurs through interactions between chemoattractant-activated chemoreceptors, CheA kinase, and other regulators including CheY, CheR, CheB, and CheZ ( Figure 2).…”