Fig. 3.

Output signals of wild-type Tsr molecules in different modification states. (A) CheA activity as a function of HAMP or MH bundle structural stability. The output curve is based on recent studies that posit a biphasic, dynamic bundle mechanism for Tsr-HAMP input-output control (73, 74). Black arrowheads denote stabilizing effects, and white arrowheads denote destabilizing effects. The flagellar rotation patterns of Tsr strains containing different combinations of CheR and CheB proteins were assessed by cell tethering (73). Tsr molecules in the absence of both CheB and CheR have a QEQE modification state, approximating a half-methylated condition (dark gray circle). In the CheB-only strain, Tsr molecules are deamidated to EEQE, QEEE, and EEEE states, corresponding to a mostly unmethylated condition (white circle). In the CheR-only strain, Tsr molecules can be methylated to QEmQE, QEQEm, and QEmQEm states, corresponding to a nearly fully methylated condition (black circle). In strains containing both CheR and CheB, Tsr molecules undergo deamidation, methylation, and demethylation reactions that drive the receptor ensemble to the adaptation set point, corresponding to a low effective methylation state (light gray circle). (B) SDS-PAGE assessment of Tsr modification states. Tsr proteins from the four hosts used for panel A were analyzed by gel electrophoresis and visualized by immunoblotting, as described in Materials and Methods. The triplet bands are a mixture of Tsr reference molecules in the EEEE, QEQE, and QQQQ modification states.