Antimicrobials that Bind to the 50S Ribosomal Subunit · 2016-02-12 · 1 Antimicrobials that Bind...

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Antimicrobials that Bind to the 50SRibosomal Subunit

Chloramphenicol, Lincomycin,Clindamycin (bacteriostatic)

• Mode of action - These antimicrobials bind to the 50S ribosome and inhibitpeptidyl transferase activity.

• Spectrum of activity - Chloramphenicol - Broad range;Lincomycin and clindamycin - Restricted range

• Resistance - Common

• Adverse effects - Chloramphenicol is toxic (bone marrow suppression) but isused in the treatment of bacterial meningitis.

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Macrolides (bacteriostatic)erythromycin, clarithromycin, azithromycin, spiramycin

• Mode of action - The macrolides inhibit translocation.

• Spectrum of activity - Gram-positive bacteria, Mycoplasma,Legionella

• Resistance - Common

Antimicrobials that Interfere withElongation Factors

Selectivity due to differences in prokaryotic and eukaryoticelongation factors

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Fusidic acid (bacteriostatic)

• Mode of action - Fusidic acid binds to elongation factor G (EF-G) andinhibits release of EF-G from the EF-G/GDP complex.

• Spectrum of activity - Gram-positive cocci

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FOOTPRINTING ANTIBIOTIC BINDIN SITES ON 16S rRNA IN 30S SUBUNITNUCLEOTIDES IN 16S RNA THAT ARE PROTECTED FROM CHEMICAL MODIFICATION

WHEN VARIOUS ANTIBIOTICS ARE BOUND TO THE 30S RIBOSOMAL SUBUNIT

ENHANCEMENT

WEAVER: FIG. 19.27

CORRELATION OF(1) SITES OF CHEMICALPROTECTION BYCHLORAMPHENICOL WITH(2) SITES OF MUTATION TO CHLORAMPHENICOLRESISTANCE IN DOMAIN VOF THE 23S RNA

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2

WEAVER: FIG. 19.28

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Fig. 18.11

Antibioticsthat inhibitproteinsynthesis bybinding toribosomes.

Inhibits PT on80S cytoplasmicribosomes

Chloramphenicolinhibits peptidyltransferase (PT)activity!

PT loop

PT loop

PT loop

Antibiotic footprints(circled bases)

Antibiotic resistance mutations(circled bases)

Antibiotics that inhibit PT bind to a loop in Domain V of 23S rRNA

PT loop – peptidyl transferase loop

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Tetra

cycl

ine

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Ant

ibio

tic M

odes

of A

ctio

n Mode of ActionDrug

Binds to D-Ala-D-Ala terminus; inhibitstranspeptidation

Vancomycin

Inhibits transpeptidation enzymes. Activates lycticenzymes of cell wall

Penicillin

Inhibits transpeptidation enzymes. Activates lycticenzymes of cell wall

Carbenicillin

Blocks RNA synthesis: binds to, inhibits DNA-dependent RNA polymerase

Rifampin

Inhibits bacterial DNA gyrase; interferes with DNA-involved activities like DNA replication

Ciprofloxacin

Interferes with protein synthesis by binding to thebacterial ribosome

Chloramphenicol

Causes misreading of mRNA: binds to 30Sribosomal subunit

Streptomycin

Interferes with synthesis of folic acid by competitionwith p-aminobenzoic acid

Sulfonamides

Disrupts structure and permeability of plasmamambrane by binding with it

Polymyxin B

from: http://project.bio.iastate.edu/Courses/MIPM302/302new/9_1chemother.html

Chl

oram

phen

icol

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Tunnel for nascent peptide

Nissen et al. (2000) Science,289, 920-930

Role of 23S rRNA (in red)

Tunnel of nascent peptide


Interactions with chaperonines or SRP?

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Diameter18 à 25 Å: no helical formation

Tunnel of nascent peptide


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Journal of Molecular BiologyVolume 330, Issue 5 , 25 July 2003, Pages 1061-1075

Structures of Five Antibiotics Bound at the PeptidylTransferase Center of the Large Ribosomal Subunit

Jeffrey L. Hansen1, Peter B. Moore1, 2 and Thomas A. Steitz, , 1, 2, 3

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Anisomycin, chloramphenicol, sparsomycin, blasticidin S, and virginiamycin Mbind to sites that overlap those of either peptidyl-tRNA or aminoacyl-tRNA, consistent with their functioning as competitive inhibitors ofpeptide bond formation.

Two hydrophobic crevices, one at the peptidyl transferase center and the otherat the entrance to the peptide exit tunnel play roles in binding these antibiotics.

Midway between these crevices, nucleotide A2103 of H. marismortui (2062Escherichia coli) varies in its conformation and thereby contacts antibioticsbound at either crevice.

The aromatic ring of anisomycin binds to the active-site hydrophobiccrevice, as does the aromatic ring of puromycin, while the aromatic ringof chloramphenicol binds to the exit tunnel hydrophobic crevice.

Sparsomycin contacts primarily a P-site bound substrate, but alsoextends into the active-site hydrophobic crevice.

Virginiamycin M occupies portions of both the A and P-site, and induces aconformational change in the ribosome.

Blasticidin S base-pairs with the P-loop and thereby mimics C74and C75 of a P-site bound tRNA.

Antimicrobials that Bind to the 50S Ribosomal Subunit · 2016-02-12 · 1 Antimicrobials that Bind...

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