Xy. Zhu et al., TYROSINE-106 OF CHEY PLAYS AN IMPORTANT ROLE IN CHEMOTAXIS SIGNAL-TRANSDUCTION IN ESCHERICHIA-COLI, Journal of bacteriology, 178(14), 1996, pp. 4208-4215
CheY is the response regulator in the signal transduction pathway of b
acterial chemotaxis. Position 106 of CheY is occupied by a conserved a
romatic residue (tyrosine or phenylalanine) in the response regulator
superfamily, A number of substitutions at position 106 have been made
and characterized by both behavioral and biochemical studies, On the b
asis of the behavioral studies, the phenotypes of the mutants at posit
ion 106 can be divided into three;categories: (i) hyperactivity, with
a tyrosine-to-tryptophan mutation (Y106W) causing increased tumble sig
naling but impairing chemotaxis; (ii) low-level activity, with a tyro
sine-to-phenylalanine change (Y106F) resulting in decreased tumble sig
naling acid chemotaxis; and (iii) no activity, with substitutions such
as Y106L, Y106I, Y106V, Y106G, and Y106C resulting in no chemotaxis a
nd a smooth-swimming phenotype. All three types of mutants can be phos
phorylated by CheA-phosphate in vitro to a level similar to that of wi
ld-type CheY. Autodephosphorylation rates are similar for all categori
es of mutants, All mutant proteins displayed less than twofold increas
ed rates compared with wild-type CheY. Binding of the mutant proteins
to FliM was similar to that of the wild-type CheY in the CheY-FliM bin
ding assays. The combined results from in vivo behavioral and in vitro
biochemical studies suggest that the diverse phenotypes of the Y106 m
utants are not due to a variation in phosphorylation or dephosphorylat
ion ability nor in affinity for the switch. With reference to the stru
ctures of wild-type CheY and the T871 CheY mutant, our results suggest
that rearrangements of the orientation of the tyrosine side chain at
position 106 are involved in the signal transduction of Chef: These da
ta also suggest that the binding of phosphoryl-CheY to the flagellar m
otor is a necessary, but not sufficient, event for signal transduction
.