MUROPEPTIDE RECYCLING PATHWAY & BETA LACTAMASE INDUCTION

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The principal objectives of this proposal are to elucidate the pathway used by E. coli for recycling muropeptides, to determine the function recycling serves in the life of the cell and to characterize the role of muropeptides in the beta-lactamase induction process. These objectives follow from our preliminary results which support the following tentative conclusions: (1) AmpG, which is required for beta-lactamase induciton, is a permease required for recycling cell wall components. (2) AmpG most likely transports N-acetylglucosaminyl-beta 1-4, 1,6 anhydro-N-acetylmuramyl-L- alanyl-D-glutamyl-(L)-meso-diaminopimelic acid (G1cNAc-anhMurNAc-L-ala-D- glu-DAP) into the cytoplasm. (3) AmpD, required for beta-lactamase inducibility is also essential for recycling. (4) ampD mutants accumulate huge amounts of anhMurNAc-L-ala-D-glu-DAP indicating that it is an inducing ligand. (5) AmpD is an anhMurNAc-1-ala amidase. Presumably the tripeptide released by the AmpD amidase is added to UDPMurNAc by a yet to be discovered tripeptide-adding enzyme thereby reintroducing L-ala-D-glu- DAP into the biosynthetic pathway. (6) G1cNAc-anhMurNAC-L-ala-D-glu-DAP is probably another inducer of beta-lactamase. Thus, based on these new results of the past 16 months, the specific aims are: 1. To study and characterize the 4 predicted steps in the recycling pathway, namely: AmpG permease, beta-N-acetylglucosaminidase, AmpD amidase, and the hypothetical tripeptide-adding enzyme. 2. To identify the muropeptides involved in beta-lactamase induction and to further characterize their role in beta-lactamase induction. 3. To search for a role of recycling in the life of the cell.