Download Antimicrobials that Bind to the 50S Ribosomal Subunit

Antimicrobials that Bind to the 50S
Ribosomal Subunit
Chloramphenicol, Lincomycin,
Clindamycin (bacteriostatic)
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Mode of action - These antimicrobials bind to the 50S ribosome and inhibit
peptidyl transferase activity.
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Spectrum of activity - Chloramphenicol - Broad range;
Lincomycin and clindamycin - Restricted range
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Resistance - Common
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Adverse effects - Chloramphenicol is toxic (bone marrow suppression) but is
used 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 with
Elongation Factors
Selectivity due to differences in prokaryotic and eukaryotic
elongation factors
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Fusidic acid (bacteriostatic)
• Mode of action - Fusidic acid binds to elongation factor G (EF-G) and
inhibits release of EF-G from the EF-G/GDP complex.
• Spectrum of activity - Gram-positive cocci
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ENHANCEMENT
FOOTPRINTING ANTIBIOTIC BINDIN SITES ON 16S rRNA IN 30S SUBUNIT
NUCLEOTIDES IN 16S RNA THAT ARE PROTECTED FROM CHEMICAL MODIFICATION
WHEN VARIOUS ANTIBIOTICS ARE BOUND TO THE 30S RIBOSOMAL SUBUNIT
WEAVER: FIG. 19.27
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CORRELATION OF
(1) SITES OF CHEMICAL
PROTECTION BY
CHLORAMPHENICOL WITH
(2) SITES OF MUTATION
TO CHLORAMPHENICOL
RESISTANCE IN DOMAIN V
OF THE 23S RNA
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WEAVER: FIG. 19.28
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Antibiotics
that inhibit
protein
synthesis by
binding to
ribosomes.
Chloramphenicol
inhibits peptidyl
transferase (PT)
activity!
Inhibits PT on
80S cytoplasmic
ribosomes
Fig. 18.11
Antibiotics that inhibit PT bind to a loop in Domain V of 23S rRNA
Antibiotic footprints
(circled bases)
PT loop
PT loop
PT loop
Antibiotic resistance mutations
(circled bases)
PT loop – peptidyl transferase loop
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Tetracycline
Mode of Action
Vancomycin
Binds to D-Ala-D-Ala terminus; inhibits
transpeptidation
Penicillin
Inhibits transpeptidation enzymes. Activates lyctic
enzymes of cell wall
Carbenicillin
Inhibits transpeptidation enzymes. Activates lyctic
enzymes of cell wall
Rifampin
Blocks RNA synthesis: binds to, inhibits DNAdependent RNA polymerase
Ciprofloxacin
Inhibits bacterial DNA gyrase; interferes with DNAinvolved activities like DNA replication
Chloramphenicol
Interferes with protein synthesis by binding to the
bacterial ribosome
Streptomycin
Causes misreading of mRNA: binds to 30S
ribosomal subunit
Sulfonamides
Interferes with synthesis of folic acid by competition
with p-aminobenzoic acid
Polymyxin B
Disrupts structure and permeability of plasma
mambrane by binding with it
from: http://project.bio.iastate.edu/Courses/MIPM302/302new/9_1chemother.html
Chloramphenicol
Antibiotic Modes of Action
Drug
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Tunnel for nascent peptide
Role of 23S rRNA (in red)
Nissen et al. (2000) Science,289, 920-930
Tunnel of nascent peptide
Interactions with chaperonines or SRP?
Nissen et al. (2000) Science,289, 920-930
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Tunnel for nascent peptide
Diameter18 à 25 Å: no helical formation
Nissen et al. (2000) Science,289, 920-930
Tunnel of nascent peptide
Nissen et al. (2000) Science,289, 920-930
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Tunnel for nascent peptide
Nissen et al. (2000) Science,289, 920-930
Journal of Molecular Biology
Volume 330, Issue 5 , 25 July 2003, Pages 1061-1075
Structures of Five Antibiotics Bound at the Peptidyl
Transferase 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 M
bind to sites that overlap those of either peptidyl-tRNA or aminoacyltRNA, consistent with their functioning as competitive inhibitors of
peptide bond formation.
Two hydrophobic crevices, one at the peptidyl transferase center and the other
at the entrance to the peptide exit tunnel play roles in binding these antibiotics.
Midway between these crevices, nucleotide A2103 of H. marismortui (2062
Escherichia coli) varies in its conformation and thereby contacts antibiotics
bound at either crevice.
The aromatic ring of anisomycin binds to the active-site hydrophobic
crevice, as does the aromatic ring of puromycin, while the aromatic ring
of chloramphenicol binds to the exit tunnel hydrophobic crevice.
Sparsomycin contacts primarily a P-site bound substrate, but also
extends into the active-site hydrophobic crevice.
Virginiamycin M occupies portions of both the A and P-site, and induces a
conformational change in the ribosome.
Blasticidin S base-pairs with the P-loop and thereby mimics C74
and C75 of a P-site bound tRNA.
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