title: Amino acid repetitions in the dihydropteroate synthase of Streptococcus pneumoniae lead to sulfonamide resistance with limited effects on substrate K(m).
abstract: Sulfonamide resistance in Streptococcus pneumoniae is due to changes in the chromosomal folP (sulA) gene coding for dihydropteroate synthase (DHPS). The first reported laboratory-selected sulfonamide-resistant S. pneumoniae isolate had a 6-bp repetition, the sul-d mutation, leading to a repetition of the amino acids Ile(66) and Glu(67) in the gene product DHPS. More recently, clinical isolates showing this and other repetitions have been reported. WA-5, a clinical isolate from Washington State, contains a 6-bp repetition in the folP gene, identical to the sul-d mutation. The repetition was deleted by site-directed mutagenesis. Enzyme kinetic measurements showed that the deletion was associated with a 35-fold difference in K(i) for sulfathiazole but changed the K(m) for p-aminobenzoic acid only 2.5-fold and did not significantly change the K(m) for 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine pyrophosphate. The enzyme characteristics of the deletion variant were identical to those of DHPS from a sulfonamide-susceptible strain. DHPS from clinical isolates with repetitions of Ser(61) had very similar enzyme characteristics to the DHPS from WA-5. The results confirm that the repetitions are sufficient for development of a resistant enzyme and suggest that the fitness cost to the organism of developing resistance may be very low.
authors.affiliation: Division of Microbiology, Department of Pharmaceutical Biosciences, Biomedical Centre, Uppsala University, Uppsala, Sweden.
authors.forename: Y
authors.initials: Y
authors.lastname: Haasum
authors.forename: K
authors.initials: K
authors.lastname: Ström
authors.forename: R
authors.initials: R
authors.lastname: Wehelie
authors.forename: V
authors.initials: V
authors.lastname: Luna
authors.forename: M C
authors.initials: MC
authors.lastname: Roberts
authors.forename: J P
authors.initials: JP
authors.lastname: Maskell
authors.forename: L M
authors.initials: LM
authors.lastname: Hall
authors.forename: G
authors.initials: G
authors.lastname: Swedberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000032:analysis; D004094:Dihydropteroate Synthase / Q000235:genetics*; D004352:Drug Resistance, Microbial / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000235:genetics; D006801:Humans; D007223:Infant; D008875:Middle Aged; D008969:Molecular Sequence Data; D011008:Pneumococcal Infections / Q000382:microbiology; D020449:Repetitive Sequences, Amino Acid / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D012694:Serine / Q000235:genetics; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D013379:Substrate Specificity; D013449:Sulfonamides / Q000494:pharmacology*; D014861:Washington
chemical_list: D004269:DNA, Bacterial; D013449:Sulfonamides; D012694:Serine; D004094:Dihydropteroate Synthase