ABSTRACT
Xiang Yang Zhu
Behavioral and Biochemical Consequences of Substitutions of Tyrosine 106 of CheY:
Evidence for An Important Role in Bacterial Chemotaxis Signal Transduction (Accepted
for publication -- Journal of Bacteriology)
Xiangyang Zhu, Charles D. Amsler, Karl Volz, and Philip Matsumura
ABSTRACT:
CheY is the response regulator in the bacterial chemotaxis signal transduction pathway. The
position 106 of CheY is a conserved aromatic 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. Based on the behavioral studies, the
phenotypes of the mutants at position 106 can be divided into three categories: 1)
hyperactivity, where a tyrosine to tryptophan mutation (Y106W) causes increased tumble
signaling but less chemotactic activity; 2) low-level activity, in which a tyrosine to
phenylalanine change (Y106F) results in decreased tumble signaling and less chemotactic
activity; and 3) no activity, where substitutions such as Y106L, Y106I, Y106V, Y106G, and
Y106C exhibit no chemotaxis at all and have a smooth swimming phenotype. All three types
of mutants can be phosphorylated by CheA-phosphate in vitro at a level similar to wild-type
CheY. Autodephosphorylation rates are similar for all categories of mutants. All displayed less
than two fold increased rates compared to wild-type CheY. Binding of the mutant proteins to
FliM was similar to the wild-type CheY in CheY-FliM binding assays. The combined results
from in vivo behavioral and in vitro biochemical studies suggest that the diverse phenotypes of
the Y106 mutants are not due to a variation in phosphorylation/dephosphorylation ability or
changes in binding affinity to the switch. Combined with the structures of wild-type CheY and
the T87I CheY mutant, our results suggest that the positional rearrangements of the tyrosine
side chain at position 106 are involved in the signal transduction of CheY. These data also
suggest that binding of CheY-P to the flagella motor is a necessary but not sufficient event for
signal transduction.
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