Editors' ChoiceBacterial Signal Transduction

The Differences That Bind

Science Signaling  26 Oct 2010:
Vol. 3, Issue 145, pp. ec330
DOI: 10.1126/scisignal.3145ec330

The chemotaxis system in bacteria links the binding of extracellular ligands to chemoreceptors to changes in flagellar motility. Major chemoreceptors (such as Tar and Tsr) are abundant and directly bind to ligands, whereas minor chemoreceptors (such as Trg and Tap) are lower in abundance and bind to ligands indirectly through periplasmic binding proteins. Chemoreceptors with different ligand specificities are clustered in allosteric signaling complexes or teams, which are synchronously inactivated or activated, thereby enabling signal integration. To measure chemoreceptor signaling, Neumann et al. (see also Underbakke and Kiessling) used a fluorescence resonance energy transfer reporter based on CheY (a motor effector protein downstream of chemoreceptors) and CheZ (a phosphatase that dephosphorylates and inactivates CheY). When differences in abundance were normalized, major and minor chemoreceptors had similar affinities for their ligands. However, major chemoreceptors had a wider dynamic range and larger response amplitudes than minor chemoreceptors. Furthermore, allosteric receptor teams showed greater response sensitivity to directly binding compared with indirectly binding ligands, a difference that was reduced when binding proteins were overexpressed. Thus, the signaling responses of minor chemoreceptors are determined by the abundance of binding proteins, and the authors suggest that direct versus indirect ligand binding may be a better way to classify major and minor chemoreceptors. These binding proteins also couple to nutrient transporters, leading the authors to propose that chemotactic and nutrient transport responses may be integrated.

S. Neumann, C. H. Hansen, N. S. Wingreen, V. Sourjik, Differences in signalling by directly and indirectly binding ligands in bacterial chemotaxis. EMBO J. 29, 3484–3495 (2010). [PubMed]

E. S. Underbakke, L. L. Kiessling, Classifying chemoreceptors: Quantity versus quality. EMBO J. 29, 3435–3436 (2010). [PubMed]