The protein CheZ, which has the last unknown structure in the
Escherichia coli chemotaxis pathway, stimulates the dephosphorylation of
the response regulator CheY by an unknown mechanism. Here we report the
co-crystal structure of CheZ with CheY, Mg2+ and the phosphoryl
analog, BeF3-. The predominant structural
feature of the CheZ dimer is a long four-helix bundle composed of two helices
from each monomer. The side chain of Gln 147 of CheZ inserts into the CheY
active site and is essential to the dephosphorylation activity of CheZ. Gln 147
may orient a water molecule for nucleophilic attack, similar to the role of the
conserved Gln residue in the RAS family of GTPases. Similarities between the
CheY−CheZ and Spo0F−Spo0B structures suggest a general mode of
interaction for modulation of response regulator phosphorylation chemistry.
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