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#penicillin

7 public questions tagged with this topic.

Microbial Physiology

Which antibiotic disrupts bacterial cell wall synthesis?

Peptidoglycan assembly begins in cytoplasm with formation of UDP-MurNAc-pentapeptide containing terminal D-alanyl-D-alanine, followed by linkage to lipid carrier undecaprenyl phosphate, also termed bactoprenol, which flips precursor across inner membrane to periplasmic side. Once externalized, class A transglycosylases polymerize glycan chains extending the sacculus and DD-transpeptidases, members of penicillin-binding protein family such as PBP1a, PBP1b, PBP2 and PBP3, catalyze crosslink between D-alanine of one stem and diamino acid of neighboring stem, releasing terminal D-alanine and formi

Ref: Walsh, Antibiotics: Actions, Origins, Resistance, ASM Press; NCBI Bookshelf, Beta-Lactam Mechanism.

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Microbial Physiology

Which enzyme is inhibited by penicillin?

Bacterial peptidoglycan final crosslinking step catalyzed by transpeptidases penicillin binding proteins class B enzymes PBP2 for elongation, PBP3 FtsI for division. They cleave C terminal D alanine D alanine dipeptide from pentapeptide side chain MurNAc L Ala D Glu mDAP D Ala D Ala, forming acyl enzyme intermediate through active site serine nucleophile, then transfer to amino group acceptor meso diamino pimelic acid or L lysine of neighboring strand creating peptide crossbridge essential for wall rigidity. Beta lactam antibiotics penicillin contain four membered ring mimicking D Ala D Ala co

Ref: Tipper & Strominger, PNAS 1965, Penicillin inhibits transpeptidase PBP crosslinking peptidoglycan.

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Microbial Physiology

β-lactam antibiotics inhibit bacterial growth by:

Peptidoglycan assembly requires synthesis of soluble UDP-N-acetylmuramyl pentapeptide in cytoplasm, attachment to undecaprenyl phosphate carrier to form Lipid II, flipping to external leaflet, polymerization by transglycosylases and final cross-linking of pentapeptide stems by transpeptidases called penicillin-binding proteins possessing active-site serine. The transpeptidase recognizes the terminal D-Ala-D-Ala motif and catalyzes cleavage of the terminal D-alanine with concomitant formation of a new peptide bond between meso-diaminopimelate or lysine and D-alanine from adjacent strand, confer

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 17: Peptidoglycan Synthesis and Beta-Lactam Action.

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SPECIES INTERACTION

Penicillin secreted by fungi harming bacteria is an example of:

Penicillin production illustrates antibiosis and is commonly classified as amensalism when susceptible bacteria are harmed while the fungus is assumed to be unaffected. Penicillin binds penicillin-binding proteins and inhibits transpeptidation of peptidoglycan, weakening the bacterial cell wall. Actively growing cells then become vulnerable to osmotic lysis. In ecological sign notation, this simplified interaction is (0, −), unlike parasitism (+, −), mutualism (+, +), or competition (−, −). However, assigning zero effect to the fungus is an assumption. If bacterial suppression releases nutrien

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13

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SPECIES INTERACTION

A fungus secreting antibiotics that kill bacteria is an example of:

Antibiotic secretion by a fungus that suppresses nearby bacteria is a standard example of amensalism, specifically antibiosis, when the fungus is treated as unaffected and the bacteria are harmed. The fungal metabolite inhibits bacterial cell-wall synthesis, protein synthesis, membrane function, or another essential process, depending on the compound. Penicillin, for instance, blocks transpeptidation during peptidoglycan assembly, causing susceptible growing cells to lyse. Ecological sign notation represents this simplified outcome as (0, −): no measurable effect on the producer and a negative

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13

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