Kinetic characterization of lipid II-Ala:alanyl-tRNA ligase (MurN) from Streptococcus pneumoniae using semisynthetic aminoacyl-lipid II substrates.

MurM and MurN are tRNA-dependent ligases that catalyze the addition of the first (L-Ala/L-Ser) and second (L-Ala) amino acid onto lipid II substrates in the biosynthesis of the peptidoglycan layer of Streptococcus pneumoniae. We have previously characterized the first ligase, MurM (Lloyd, A. J.

Characterization of tRNA-dependent peptide bond formation by MurM in the synthesis of Streptococcus pneumoniae peptidoglycan.

MurM is an aminoacyl ligase that adds l-serine or l-alanine as the first amino acid of a dipeptide branch to the stem peptide lysine of the pneumococcal peptidoglycan. MurM activity is essential for clinical pneumococcal penicillin resistance. Analysis of peptidoglycan from the highly penicillin-resistant Streptococcus pneumoniae strain 159 revealed that in vivo and in vitro, in the presence of the appropriate acyl-tRNA, MurM(159) alanylated the peptidoglycan epsilon-amino group of the stem peptide lysine in preference to its serylation.

Proinflammatory activation of Toll-like receptor-2 during exposure of penicillin-resistant Streptococcus pneumoniae to beta-lactam antibiotics.

Objectives: Disease caused by penicillin-resistant Streptococcus pneumoniae (PRSP) is associated with more suppurative complications than disease caused by penicillin-susceptible S. pneumoniae (PSSP). Exposure of S.

Incremental increase in fitness cost with increased beta -lactam resistance in pneumococci evaluated by competition in an infant rat nasal colonization model.

Background: We evaluated the impact of resistant penicillin-binding protein (PBP) allele acquisition on the ability of penicillin-resistant (PEN-R) pneumococcal strains to compete with penicillin-susceptible (PEN-S) ancestors for upper-respiratory-tract (URT) colonization.

Methods: PEN-S serotype 2, 6B, and 9V strains were transformed into derivatives expressing an increasing number of PEN-R PBP forms (2X, 2X-1A, and 2X-1A-2B for serotype 2 and 2X, 2X-2B, and 2X-2B-1A for 6B and 9V). Infant rats were inoculated intranasally with a mix of a PEN-R and PEN-S strains.

Phospho-N-acetyl-muramyl-pentapeptide translocase from Escherichia coli: catalytic role of conserved aspartic acid residues.

Phospho-N-acetyl-muramyl-pentapeptide translocase (translocase 1) catalyzes the first of a sequence of lipid-linked steps that ultimately assemble the peptidoglycan layer of the bacterial cell wall. This essential enzyme is the target of several natural product antibiotics and has recently been the focus of antimicrobial drug discovery programs. The catalytic mechanism of translocase 1 is believed to proceed via a covalent intermediate formed between phospho-N-acetyl-muramyl-pentapeptide and a nucleophilic amino acid residue.