Mutational replacements at the "glycine hinge" of the E. coli chemoreceptor Tsr support a signaling role for the C-helix residue

HERRERA SEITZ, MARÍA KARINA; MASSAZZA, DIEGO ARIEL; PEDETTA, ANDREA; STUDDERT, CLAUDIA ALICIA

BIOCHEMISTRY

AMER CHEMICAL SOC

Año: 2017

0006-2960

Bacterial chemoreceptors are dimeric membrane proteins that transmit signals from a periplasmic ligand-binding domain to the interior of the cells. The highly conserved cytoplasmic domain consists of a long hairpin that in the dimer forms a 4-helix coiled-coil bundle. The central region of the bundle couples changes in helix packing that occur in the membrane proximal region to the signaling tip, controlling the activity of an associated histidine kinase. This subdomain contains certain glycine residues that are postulated to form a hinge in chemoreceptors from enteric bacteria and have been largely postulated to play a role in the coupling mechanism, and/or in the formation of higher-order chemoreceptor assemblies. In this work we directly assessed the importance of the ?glycine hinge? by obtaining non-functional replacements at each of its positions in the E. coli serine receptor Tsr, and characterizing them. Our results indicate that, rather than being essential for proper receptor-receptor interaction, the ?glycine hinge? residues are involved in the receptor ability to switch between different signaling states. Mainly, the C-helix residue G439 has a key role in shifting the equilibrium towards a kinase-activating conformation. However, we found second-site mutations that restore the chemotactic proficiency of some of the ?glycine hinge? mutants, suggesting that a complete hinge is not strictly essential. Rather, glycine residues seem to favor the coupling activity that relies in some other structural features of the central subdomain.