Lloyd, Adrian J., Gilbey, Andrea M., Blewett, Anne M., De Pascale, Gianfranco, El Zoeiby, Ahmed, Levesque, Roger C., Catherwood, Anita C., Tomasz, Alexander, Bugg, Tim, Roper, David I. and Dowson, Christopher G.. (2008) Characterization of tRNA-dependent peptide bond formation by MurM in the synthesis of Streptococcus pneumoniae peptidoglycan. Journal of Biological Chemistry, Vol.283 (No.10). pp. 6402-6417. ISSN 0021-9258

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Abstract

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. However, in contrast, identical analyses of the penicillin-susceptible strain Pn16 revealed that MurM(Pn16) activity supported serylation more than alanylation both in vivo and in vitro. Interestingly, both MurMPn16 acylation activities were far lower than the alanylation activity of MurM159. The resulting differing stem peptide structures of 159 and Pn16 were caused by the profoundly greater catalytic efficiency of MurM159 compared with MurMPn16 bought about by sequence variation between these enzymes and, to a lesser extent, differences in the in vivo tRNAAla: tRNASer ratio in 159 and Pn16. Kinetic analysis revealed that MurM159 acted during the lipid-linked stages of peptidoglycan synthesis, that the D-alanyl-D-alanine of the stem peptide and the lipid II N-acetylglucosaminyl group were not essential for substrate recognition, that epsilon-carboxylation of the lysine of the stem peptide was not tolerated, and that lipid II-alanine was a substrate, suggesting an evolutionary link to staphylococcal homologues of MurM such as FemA. Kinetic analysis also revealed that MurM recognized the acceptor stem and/or the T Psi C loop stem of the tRNAAla. It is anticipated that definition of the minimal structural features of MurM substrates will allow development of novel resistance inhibitors that will restore the efficacy of beta-lactams for treatment of pneumococcal infection.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry Q Science > QP Physiology
Divisions:	Faculty of Science > Chemistry Faculty of Science > Life Sciences (2010- )
Library of Congress Subject Headings (LCSH):	Streptococcus pneumoniae, Transfer RNA, Peptidoglycans -- Synthesis, Peptides
Journal or Publication Title:	Journal of Biological Chemistry
Publisher:	American Society for Biochemistry and Molecular Biology
ISSN:	0021-9258
Date:	7 March 2008
Volume:	Vol.283
Number:	No.10
Number of Pages:	16
Page Range:	pp. 6402-6417
Identification Number:	10.1074/jbc.M708105200
Status:	Peer Reviewed
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/30468

Data sourced from Thomson Reuters' Web of Knowledge

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