Chemoreceptor complexes signal through a protein-ordering and stabilization mechanism

Membrane protein complexes are critical to many cellular processes and have proven to be good targets for a variety of therapeutics. One such complex is the bacterial chemoreceptor signaling complex, which has potential as a target for novel antibiotics. This complex is responsible for sensing chemical signals in the environment to bias swimming of the bacterial cell toward more favorable conditions. While these complexes are well studied, the mechanisms of signal transduction and kinase control are still not fully understood. We have applied multiple thermal stability measurements and limited proteolysis to gain insight into how complex formation and signaling state change the thermal stability and structural properties of the proteins and complexes. We show that the activated signaling complexes are more strongly associated, ordered, and thermally stable than the inactive complexes. This direct evidence that both the chemoreceptor and the kinase are significantly stabilized by assembly into kinase-active complexes is consistent with our previous hydrogen deuterium exchange mass spectrometry results and our proposed order-induced activation model. We propose that signaling inputs modulate the structural order and stability of the partially disordered cytoplasmic domain, which in turn modulates the stability of the catalytic domain of the kinase, such that ordering of the cytoplasmic domain stabilizes and activates the kinase.