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The Role of GyrB in the DNA Cleavage-religation Reaction of DNA Gyrase: A Proposed Two Metal-ion Mechanism
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Abstract
We have examined the role of the DNA gyrase B protein in cleavage and religation of
DNA using site-directed mutagenesis. Three aspartate residues and a glutamate residue:
E424, D498, D500 and D502, thought to co-ordinate a magnesium ion, were mutated to
alanine; in addition, the glutamate residue and one aspartate residue were mutated
to glutamine and asparagine, respectively. We have shown that these residues are important
for the cleavage-religation reaction and are likely to be involved in magnesium ion
co-ordination. On separate mutation of two of these aspartate residues to cysteine
or histidine, the metal ion preference for the DNA relaxation activity of gyrase changed
from magnesium to manganese (II). We present evidence to support the idea that cleavage
of each DNA strand involves two or more metal ions, and suggest a scheme for the DNA
cleavage chemistry of DNA gyrase involving two metal ions.
(c) 2002 Elsevier Science Ltd.