Synthesis of mosaic peptidoglycan cross-bridges by hybrid peptidoglycan assembly pathways in gram-positive bacteria.
The peptidoglycan cross-bridges of Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium consist of the sequences Gly(5), l-Ala(2), and d-Asx, respectively. Expression of the fmhB, femA, and femB genes of S. aureus in E. faecalis led to the production of peptidoglycan precursors substituted by mosaic side chains that were efficiently used by the penicillin-binding proteins for cross-bridge formation. The Fem transferases were specific for incorporation of glycyl residues at defined positions of the side chains in the absence of any additional S. aureus factors such as tRNAs used for amino acid activation. The PBPs of E. faecalis displayed a broad substrate specificity because mosaic side chains containing from 1 to 5 residues and Gly instead of l-Ala at the N-terminal position were used for peptidoglycan cross-linking. Low affinity PBP2a of S. aureus conferred beta-lactam resistance in E. faecalis and E. faecium, thereby indicating that there was no barrier to heterospecific expression of resistance caused by variations in the structure of peptidoglycan precursors. Thus, conservation of the structure of the peptidoglycan cross-bridges in members of the same species reflects the high specificity of the enzymes for side chain synthesis, although this is not essential for the activity of the PBPs.
INSERM E0004, Laboratoire de Recherche Moléculaire sur les Antibiotiques, 15 rue de l'Ecole de Médecine, 75270 Paris, cedex 06, France.
Ana
A
Arbeloa
Jean-Emmanuel
JE
Hugonnet
Anne-Charlotte
AC
Sentilhes
Nathalie
N
Josseaume
Lionnel
L
Dubost
Christelle
C
Monsempes
Didier
D
Blanot
Jean-Paul
JP
Brouard
Michel
M
Arthur
D000595:Amino Acid Sequence; D013293:Enterococcus faecalis / Q000378:metabolism; D016984:Enterococcus faecium / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000378:metabolism*; D010457:Peptidoglycan / Q000096:biosynthesis* / Q000737:chemistry; D010458:Peptidyl Transferases / Q000378:metabolism; D013211:Staphylococcus aureus / Q000378:metabolism; D013379:Substrate Specificity
D010457:Peptidoglycan; D010458:Peptidyl Transferases