Mutational Replacements at the "Glycine Hinge" of the Escherichia coli Chemoreceptor Tsr Support a Signaling Role for the C‑Helix Residue

PEDETTA, ANDREA; STUDDERT, CLAUDIA A.; HERRERA SEITZ, MARÍA K.; MASSAZZA, DIEGO A.

BIOCHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2017 vol. 56 p. 3850 - 3862

0006-2960

Bacterial chemoreceptors are dimeric membraneproteins that transmit signals from a periplasmic ligandbindingdomain to the interior of the cells. The highlyconserved cytoplasmic domain consists of a long hairpin thatin the dimer forms a four-helix coiled-coil bundle. The centralregion of the bundle couples changes in helix packing thatoccur in the membrane proximal region to the signaling tip,controlling the activity of an associated histidine kinase. Thissubdomain contains certain glycine residues that are postulatedto form a hinge in chemoreceptors from enteric bacteria and have been largely postulated to play a role in the couplingmechanism, and/or in the formation of higher-order chemoreceptor assemblies. In this work, we directly assessed the importanceof the ?glycine hinge? by obtaining nonfunctional replacements at each of its positions in the Escherichia coli serine receptor Tsrand characterizing them. Our results indicate that, rather than being essential for proper receptor−receptor interaction, the?glycine hinge? residues are involved in the ability of the receptor to switch between different signaling states. Mainly, the C-helixresidue G439 has a key role in shifting the equilibrium toward a kinase-activating conformation. However, we found second-sitemutations that restore the chemotactic proficiency of some of the ?glycine hinge? mutants, suggesting that a complete hinge isnot strictly essential. Rather, glycine residues seem to favor the coupling activity that relies on some other structural features ofthe central subdomain.