Association of fusidic acid sensitivity with G factor in a protein-synthesizing system

Polymyxin B and fusidic acid, a novel potent synergistic combination against Klebsiella pneumoniae and Escherichia coli isolates with polymyxin B resistance

The increasing prevalence of multidrug-resistant (MDR) Gram-negative bacteria and comparatively limited options of antibiotics pose a major threat to public health worldwide. Polymyxin B is the last resort against extensively resistant Gram-negative bacterial infections. However, a large number of Gram-negative bacteria exhibited high-level resistance to Polymyxin B, bringing challenges for antimicrobial chemotherapy. Combination therapies using polymyxins and other antibiotics are recommended to treat multidrug-resistant pathogens. In this study, we selected Gram-negative bacterial strains, including Klebsiella pneumoniae and Escherichia coli, to explore whether fusidic acid and polymyxin B have a synergistic killing effect. Through broth microdilution, we observed that minimum inhibitory concentrations (MICs) against polymyxin B in the isolates tested were significantly reduced by the addition of fusidic acid. Notably, chequerboard analysis indicated a synergistic effect between polymyxin B and fusidic acid. In addition, subsequent time-kill experiments showed that the combination of polymyxin B and fusidic acid was more effective than a single drug in killing bacteria. Finally, our investigation utilizing the murine model revealed a higher survival rate in the combination therapy group compared to the monotherapy group. Our research findings provide evidence of the synergistic effect between polymyxin B and fusidic acid. Fusidic acid was shown to increase the sensitivity of multi-drug resistant E. coli and K. pneumoniae to polymyxin B, thereby enhancing its bactericidal activity. This study provides new insights into a potential strategy for overcoming polymyxin B resistance, however, further investigations are required to evaluate their feasibility in real clinical settings.

Bioactivities and Structure-Activity Relationships of Fusidic Acid Derivatives: A Review

Fusidic acid (FA) is a natural tetracyclic triterpene isolated from fungi, which is clinically used for systemic and local staphylococcal infections, including methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci infections. FA and its derivatives have been shown to possess a wide range of pharmacological activities, including antibacterial, antimalarial, antituberculosis, anticancer, tumor multidrug resistance reversal, anti-inflammation, antifungal, and antiviral activity in vivo and in vitro. The semisynthesis, structural modification and biological activities of FA derivatives have been extensively studied in recent years. This review summarized the biological activities and structure-activity relationship (SAR) of FA in the last two decades. This summary can prove useful information for drug exploration of FA derivatives.

Structure and function of FusB: an elongation factor G-binding fusidic acid resistance protein active in ribosomal translocation and recycling

Fusidic acid (FA) is a bacteriostatic antibiotic that locks elongation factor G (EF-G) to the ribosome after GTP hydrolysis during elongation and ribosome recycling. The plasmid pUB101-encoded protein FusB causes FA resistance in clinical isolates of Staphylococcus aureus through an interaction with EF-G. Here, we report 1.6 and 2.3 Å crystal structures of FusB. We show that FusB is a two-domain protein lacking homology to known structures, where the N-terminal domain is a four-helix bundle and the C-terminal domain has an alpha/beta fold containing a C4 treble clef zinc finger motif and two loop regions with conserved basic residues. Using hybrid constructs between S. aureus EF-G that binds to FusB and Escherichia coli EF-G that does not, we show that the sequence determinants for FusB recognition reside in domain IV and involve the C-terminal helix of S. aureus EF-G. Further, using kinetic assays in a reconstituted translation system, we demonstrate that FusB can rescue FA inhibition of tRNA translocation as well as ribosome recycling. We propose that FusB rescues S. aureus from FA inhibition by preventing formation or facilitating dissociation of the FA-locked EF-G–ribosome complex.

Fusidic acid is an effective treatment against Toxoplasma gondii and Listeria monocytogenes in vitro, but not in mice

Fusidic acid is a bacteriostatic antibiotic that inhibits the growth of bacteria by preventing the release of translation elongation factor G (EF-G) from the ribosome. The apicomplexan parasite Toxoplasma gondii has an orthologue of bacterial EF-G that can complement bacteria and is necessary for parasite virulence. Fusidic acid has been shown to be effective in tissue culture against the related pathogen Plasmodium falciparum, and current drug treatments against T. gondii are limited. We therefore investigated the therapeutic value of fusidic acid for T. gondii and found that the drug was effective in tissue culture, but not in a mouse model of infection. To determine whether this trend would occur in another intracellular pathogen that elicits a T helper 1-type immune response, we tested the efficacy of fusidic acid for the bacterium Listeria monocytogenes. Similar to its effects on T. gondii, fusidic acid inhibits the growth of L. monocytogenes in vitro, but not in mice. These findings highlight the necessity of in vivo follow-up studies to validate in vitro drug investigations.

In vivo selection of conditional-lethal mutations in the gene encoding elongation factor G of Escherichia coli

The ribosome translocation step that occurs during protein synthesis is a highly conserved, essential activity of all cells. The precise movement of one codon that occurs following peptide bond formation is regulated by elongation factor G (EF-G) in eubacteria or elongation factor 2 (EF-2) in eukaryotes. To begin to understand molecular interactions that regulate this process, a genetic selection was developed with the aim of obtaining conditional-lethal alleles of the gene (fusA) that encodes EF-G in Escherichia coli. The genetic selection depends on the observation that resistant strains arose spontaneously in the presence of sublethal concentrations of the antibiotic kanamycin. Replica plating was performed to obtain mutant isolates from this collection that were restrictive for growth at 42 degrees C. Two tightly temperature-sensitive strains were characterized in detail and shown to harbor single-site missense mutations within fusA. The fusA100 mutant encoded a glycine-to-aspartic acid change at codon 502. The fusA101 allele encoded a glutamine-to-proline alteration at position 495. Induction kinetics of beta-galactosidase activity suggested that both mutations resulted in slower elongation rates in vivo. These missense mutations were very near a small group of conserved amino acid residues (positions 483 to 493) that occur in EF-G and EF-2 but not EF-Tu. It is concluded that these sequences encode a specific domain that is essential for efficient translocase function.

Novel mutants of elongation factor G

A novel mutant form of elongation factor G (EF-G) in Escherichia coli is described. This variant EF-G restricts reading frame errors by a factor of 2 to 3 in vivo at two different positions in a lacIZ fusion. In addition, a conventional fusidic acid resistant (fusR) mutant of EF-G was compared with the restrictive mutant. Both mutants were characterized in vitro in a steady-state poly(U) translating system. The data indicate that the restrictive EF-G variant has an altered interaction with the ribosome both in vivo and in vitro. In contrast, the conventional fusR variant is altered in its interaction with GTP, which is evident in vitro.

Some characteristics of and structural requirements for the interaction of 24,25-dihydrofusidic acid with ribosome - elongation factor g Complexes

Fusidic acid inhibits polypeptide chain elongation by binding to the ribosome - elongation factor-G - GDP complex and thereby preventing its dissociation. The experiments reported here quantitate the interaction of the antibiotic [3H]-24,25-dihydrofusidic acid, an active analog of fusidic acid, with the ribosome - elongation factor-G - GDP comples. All components of the complex are essential for [3H]-24,25-dihydrofusidic acid binding. The stoichiometry of the interaction is ca. 1:1, and the Ka apparent, as determined by equilibrium dialysis, is 2.6 times 10-6 M-minus 1. It is further shown that GTP and GDP are equally effective in forming complexes to which the antibiotic may bind, whereas GMP and beta,gamma-methyleneguanosine triphosphate will not form complexes to which the antibiotic may bind. In order to examine the structural basis of the mode of antibiotic action shown by fusidic acid, we have considered two activities of 21 structural analogs of this antibiotic: ability to bind to the aforementioned ternary complex and ability to stabilize this complex. The comparative binding capability of the analogs were extablished through competition experiments with [3H]-24,25-dihydrofusidic acid. The data obtained from these experiments can be summarized as follows. (1) The C17-20 double bond of fusidic acid appears to be critical for both binding and complex stabilization activities. (2) A carboxyl group in the vicinity of the C20 carbon is also essential for both activities. (3) Modifications of other functional groups in the molecule can lead to significantly decreased stabilization of the ternary ribosome complex and/or ability to compete with [3H]-24,25-dihydrofusidic acid for binding to the complex, but do not demonstrate absolute structural requirements for either activity.

An Escherichia coli mutant with an altered elongation factor Tu

A thermosensitive mutant of Escherichia coli has been isolated that is unable to replicate the bacteriophage MS2 at 42 degrees but permits phage production at 37 degrees . Thermal inactivation studies of the supernatant enzymes show that this mutant contains a factor essential for the polymerization of phenylalanine from phenylalanyl-tRNA that at 50 degrees is more rapidly inactivated than the corresponding wild-type factor. The elongation factor Tu (EF-Tu) was isolated and purified to apparent homogeneity as the EF-Tu.GDP complex, both from mutant and wild-type cells. Addition of purified wild-type EF-Tu.GDP to reaction mixtures fully restored the activity of thermally inactivated mutant supernatants. These experiments excluded EF-Ts as the thermolabile factor involved. Similar inactivation studies, dealing with the purified factors and performed in reaction mixtures that were not supplemented with GDP, revealed that the half-life of mutant EF-Tu.GDP at 50 degrees was 1.5 min, that of the wild-type factor 6 min. Addition of GDP (10muM) to the medium reduced the inactivation rate of both wild-type and mutant factor and also the difference in inactivation kinetics. Besides the altered elongation factor Tu, the mutant skill contains a second mutation affecting the glutaminyl-tRNA synthetase.

Residual polarity and transcription-translation coupling during recovery from chloramphenicol or fusidic acid

Fusidic acid or chloramphenicol was used to inhibit peptide synthesis to 1% of normal in Escherichia coli B, strain AS19. After 10 min of inhibition, peptide synthesis could be quickly restored to 80% of the normal rate after washing the bacteria on a filter. However, even in the presence of adenosine 3'-5'-cyclic-monophosphoric acid to block catabolite repression, beta-galactosidase, the first enzyme of the lactose operon (lac), could only be induced to 10% of normal, and the last enzyme of the operon, galactoside acetyltransferase, even less. The first and last enzymes of the operon for tryptophan synthesis could be derepressed to about 30% of normal. The lac ribonucleic acid (RNA) induced during recovery showed a smaller than normal size distribution on sucrose gradients. The operator-proximal or -distal parts of this RNA were specifically labeled. Hybridization to phi80dlac deoxyribonucleic acid (DNA) suggested that although the distal parts of the lac RNA were barely detectable, initiation was occurring at normal rates in recovery. Either normal levels of distal messenger RNA (mRNA) are made but then rapidly degraded or the mRNA is not completed. The small amount that is made decayed abnormally slowly, probably as a result of slower transcription. Total mRNA decay was multiphasic with all components decaying slower than normal. We propose that there is a residual level of inhibition of peptide synthesis during recovery. The probability that a ribosome is blocked at any codon can be estimated from the data. The longer the message, the less likely its complete translation. We propose that the RNA polymerase can transcribe translatable mRNA for only a finite distance beyond the lead ribosome. Because ribosomes can load at the start of each message in a polycistronic mRNA, the probability that a distal message will be synthesized and translated is a function of the number of more proximal messages and the distances between their ribosome-loading sites.

Messenger ribonucleic acid synthesis and degradation in Escherichia coli during inhibition of translation

Various aspects of the coupling between the movement of ribosomes along messenger ribonucleic acids (mRNA) and the synthesis and degradation of mRNA have been investigated. Decreasing the rate of movement of ribosomes along an mRNA does not affect the rate of movement of some, and possibly most, of the RNA polymerases transcribing the gene coding for that mRNA. Inhibiting translation with antibiotics such as chloramphenicol, tetracycline, or fusidic acid protects extant mRNA from degradation, presumably by immobilizing ribosomes, whereas puromycin exposes mRNA to more rapid degradation than normal. The promoter distal (3') portion of mRNA, synthesized after ribosomes have been immobilized by chloramphenicol on the promoter proximal (5') portion of the mRNA, is subsequently degraded.

Chromosomal localization of the structural genes of the polypeptide chain elongation factors

A survey of the polypeptide chain elongation factors in potentially sexually compatible genera was carried out. Factors from Escherichia coli and Proteus mirabilis were found to be clearly distinguishable by immunochemical and electrophoretic techniques. Mapping of the structural genes of these factors was undertaken by a study of the gene products in genetically defined E. coli-P. mirabilis hybrid diploid strains. It was found that the EF G factor mapped within 5 min of the streptomycin resistance locus, but the EF Ts factor did not map in this region.

Mammalian peptide chain termination. II. Codon specificity and GTPase activity of release factor

In vitro peptide chain termination with release factor preparations from rabbit reticulocytes, guinea pig liver, or Chinese hamster liver is directed with UAAA, UAGA, or UGAA, suggesting that UAA, UAG, and UGA are terminator condons for mammalian cells. Purified release factor from rabbit reticulocytes has ribosomaldependent GTPase activity, which is stimulated by UAAA. GTP hydrolysis appears requisite for in vitro peptide chain termination in mammals.

Inhibition of polyuridylic acid-directed protein synthesis by aurintricarboxylate in extracts of Escherichia coli

Aurintricarboxylic acid (ATA) inhibits protein synthesis directed by polyuridylic acid. All steps tested are inhibited by ATA. We conclude that inhibition of polyphenylalanine formation is an additive effect of inhibition of various steps in the protein synthetic machinery.

Binding of adenosine 3':5'-cyclic phosphate to G factor of Escherichia coli, and its effects on GTPase, RNase V, and protein synthesis

Unique among adenine nucleotides tested by filter binding assays, 3':5'-cyclic AMP binds to the G translocation factor. Binding is dependent on the presence of GTP, and is inhibited by GDP, by the analog 5'-beta,gamma-methylene GTP, and by the antibiotic fusidic acid. The cAMP seems to be released during the ribosome-dependent translocation of charged tRNA catalyzed by G factor. Bound cAMP inhibits GTPase and ribosome-associated degradation of messenger RNA, but does not inhibit protein synthesis. cAMP might thereby regulate the ratio of productive to degradative transits of ribosomes on messenger RNA, and this may account for some part of its profound effect on levels of specific bacterial messenger RNA species.

Ribonuclease V of escherichia coli. I. Dependence on ribosomes and translocation

A new RNase activity, tentatively named RNase V, was found in cell-free extracts of E. coli. This activity requires ribosomes, G and T factors, tRNA, K(+) or NH(4) (+), Mg(2+), GTP, and a sulfhydryl compound to degrade poly U, poly A, T4 phage mRNA, or E. coli mRNA. RNase V is specific for mRNA; it does not attack ribosomal RNA. It is inhibited by antibiotics that decrease breakdown of mRNA in vivo, such as chloramphenicol and streptomycin, and by such agents as 5'-beta, gamma-methylene-guanosine triphosphate, and fusidic acid, which inhibit ribosome-dependent GTPase and translocation of ribosomes along mRNA. The evidence suggests that RNase V is either an integral part of the ribosome or is tightly associated with it, and that it selectively degrades mRNA in intact cells.