Previous Article | Next Article ![]()
J. Bacteriol., Feb 1997, 831-837, Vol 179, No. 3
C Fermer and G Swedberg
Previously, the effects of three point mutations (at amino acid positions
31, 84, and 194) in the gene coding for a sulfonamide- resistant
dihydropteroate synthase of Neisseria meningitidis were analyzed by
site-directed mutagenesis. Changes at positions 31 and 194 abolished the
phenotypic expression of sulfonamide resistance, while a change at position
84 appeared to be neutral. These studies are here extended to correlate the
alterations in phenotype with effects on enzyme kinetics by expressing the
cloned meningococcal genes in an Escherichia coli strain that had its dhps
gene partially deleted and replaced by a resistance determinant. The most
dramatic effects were produced by mutations at position 31. A change from
the Leu found in the resistant isolate to a Phe (the residue found in
sensitive isolates) led to a 10-fold decrease in the Km and a concomitant
drop in the Ki. Changes at position 194 also affected both the Km and Ki
but not to the same extent as mutations at position 31. Changing position
84 altered the Km only slightly but significantly. This latter change was
interpreted as a compensatory change modulating the function of the enzyme.
In another type of resistance gene, 2 amino acid residues, proposed to be
an insertion, were deleted, resulting in a sensitive enzyme. However, the
resulting Km was raised 10-fold, suggesting that compensatory changes have
accumulated in this type of resistance determinant as well. This resistance
gene differs by as much as 10% from the sensitive isolates, which makes
identification of important mutations difficult.
Copyright © 1997, American Society for Microbiology
Adaptation to sulfonamide resistance in Neisseria meningitidis may have required compensatory changes to retain enzyme function: kinetic analysis of dihydropteroate synthases from N. meningitidis expressed in a knockout mutant of Escherichia coli
Department of Pharmaceutical Biosciences, Division of Microbiology, Faculty of Pharmacy, Uppsala University, Sweden.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»