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Nucleotide sequences of genes encoding penicillin-binding proteins from Streptococcus pneumoniae and Streptococcus oralis with high homology to Escherichia coli penicillin-binding proteins 1a and 1b.

ABSTRACT: The nucleotide sequence of a 3,378-bp DNA fragment of Streptococcus pneumoniae that included the structural gene for penicillin-binding protein (PBP) 1a (ponA), which encodes 719 amino acids, was determined. Homologous DNA fragments from an S. oralis strain were amplified with ponA-specific oligonucleotides. The 2,524-bp S. oralis sequence contained the coding region for the first 636 amino acids of a PBP. The coding sequence differed by 437 nucleotides (27%) and one additional triplet, resulting in 87 amino acid substitutions (14%), from S. pneumoniae PBP 1a. Both PBPs are highly homologous to bifunctional high-M(r) Escherichia coli PBPs 1a and 1b.

SUBMITTER: Martin C

PROVIDER: S-EPMC206242 | biostudies-other | 1992 Jul

REPOSITORIES: biostudies-other

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Nucleotide sequences of genes encoding penicillin-binding proteins from Streptococcus pneumoniae and Streptococcus oralis with high homology to Escherichia coli penicillin-binding proteins 1a and 1b.

Martin C C Briese T T Hakenbeck R R

Journal of bacteriology 19920701 13

The nucleotide sequence of a 3,378-bp DNA fragment of Streptococcus pneumoniae that included the structural gene for penicillin-binding protein (PBP) 1a (ponA), which encodes 719 amino acids, was determined. Homologous DNA fragments from an S. oralis strain were amplified with ponA-specific oligonucleotides. The 2,524-bp S. oralis sequence contained the coding region for the first 636 amino acids of a PBP. The coding sequence differed by 437 nucleotides (27%) and one additional triplet, resultin ...[more]

PMID: 1624444

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Project description:High-level penicillin resistance in pneumococci is due to alterations in penicillin-binding proteins (PBPs) 2X, 2B, and 1A. We have sequenced the penicillin-binding domain of PBP 1A from penicillin-resistant South African pneumococcal isolates and have identified amino acid substitutions which are common to all the resistant isolates analyzed. Site-directed mutagenesis was then used to determine whether particular amino acid substitutions at specific positions in PBP 1A mediate penicillin resistance. PCR was used to isolate PBP 2X, 2B, and 1A genes from clinical isolate 8303 (penicillin MIC, 4 micrograms/ml). These wild-type PBP genes were cloned into pGEM-3Zf and were used as the transforming DNA. Susceptible strain R6 (MIC, 0.015 microgram/ml) was first transformed with PBP 2X and 2B DNA, resulting in PBP 2X/2B-R6 transformants for which MICs were 0.25 microgram/ml. When further transformed with PBP 1A DNA, 2X/2B/1A-R6 transformants for which MICs were 1.5 micrograms/ml were obtained. Site-directed mutagenesis of the PBP 1A gene from isolate 8303 was then used to reverse particular amino acid substitutions, followed by transformation of PBP 2X/2B-R6 transformants with the mutagenized PBP 1A DNA. For PBP 2X/2B/1A-R6 transformants, the introduction of the reversal of Thr-371 by Ser or Ala in PBP 1A decreased the MIC from 1.5 to 0.5 micrograms/ml, whereas the reversal of four consecutive amino acid substitutions (Thr-574 by Asn, Ser-575 by Thr, Gln-576 by Gly, and Phe-577 by Tyr) decreased the MIC from 1.5 to 0.375 micrograms/ml. These data reveal that amino acid residue 371 and residues 574 to 577 of PBP 1A are important positions in PBP 1A with respect to the interaction with penicillin and the development of resistance.

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Project description:We determined the nucleotide sequence between 1,903 and 3,097 bp of pbp1a, which encodes the transpeptidase domain of PBP 1A, from clinical isolates of penicillin-resistant Streptococcus pneumoniae (PRSP) serotypes 19 (n = 8), 6 (n = 9), 23 (n = 6), and 14 (n = 2) and two penicillin-susceptible S. pneumoniae (PSSP) isolates. These serotyped PRSP strains were isolated predominantly in Japan from 1993 through 1997. The 25 resistant strains were classified into five groups on the basis of the extent of sequence differences. Strains in groups I (n = 5; serotype 6), II (n = 3; serotype 19), and III (n = 12; different serotypes) had sequences highly homologous to the sequence of pbp1a of PRSP strains from South Africa, Spain, and the United States. The group IV strain (n = 1; serotype 14) had unique deletions from or insertions in the sequences. The sequences of group V strains (n = 4; serotypes 6 and 23) had relatively few differences from the sequences of the PSSP strains. For strains (n = 18) for which the threonine at codon 371 (Thr-371) in a conserved STMK motif of PBP 1A was substituted with an alanine or a serine (in addition to having altered pbp2x and pbp2b genes), penicillin MICs were >/= 1.0 microgram/ml. The PBPs 1A of these strains showed decreased affinities for [3H]benzylpenicillin and slightly faster mobilities on sodium dodecyl sulfate-polyacrylamide gels. In contrast, for strains (n = 4) without a substitution at Thr-371 in PBP 1A but with mutations in both pbp2x and pbp2b, penicillin MICs were 0.125 to 0.25 microgram/ml, and the affinities of their PBPs 1A were similar to that of PSSP PBPs 1A. Furthermore, for the Thr-371-substituted strains (n = 3) with altered pbp2x genes but native pbp2b genes, penicillin MICs were 0.125 to 0.25 microgram/ml. These results suggest that amino acid substitution of Thr-371 contributes to the development of penicillin resistance in PRSP strains with altered pbp2x and pbp2b genes.

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