scholarly journals gyrA Mutations in Ciprofloxacin-Resistant Bartonella bacilliformis Strains Obtained In Vitro

2003 ◽  
Vol 47 (1) ◽  
pp. 383-386 ◽  
Author(s):  
Michael F. Minnick ◽  
Zachary R. Wilson ◽  
Laura S. Smitherman ◽  
D. Scott Samuels
Keyword(s):  
Single Point ◽  
Point Mutations ◽  
Dna Gyrase ◽  
Wild Type ◽  
Bartonella Bacilliformis ◽  
E Coli ◽  
A Subunit ◽  
Resistant Strains ◽  
Single Point Mutations

ABSTRACT We isolated and characterized mutants of Bartonella bacilliformis that are resistant to the fluoroquinolone antibiotic ciprofloxacin, which targets the A subunit of DNA gyrase. Mutants had single point mutations in the gyrA gene that changed either Asp-90 to Gly or Asp-95 to Asn and had 3- or 16-fold higher resistance, respectively, to ciprofloxacin than did wild-type B. bacilliformis. Asp-95 is homologous to Asp-87 of Escherichia coli GyrA and is a common residue mutated in fluoroquinolone-resistant strains of other bacteria. This is the first report of a mutation at an Asp-90 homologue, which corresponds to Asp-82 in E. coli GyrA.

scholarly journals HIV recombination: what is the impact on antiretroviral therapy?

2005 ◽  
Vol 2 (5) ◽  
pp. 489-503 ◽  
Author(s):  
Christophe Fraser
Keyword(s):  
Antiretroviral Therapy ◽  
Single Point ◽  
Point Mutations ◽  
Wild Type Virus ◽  
Wild Type ◽  
Genetic Barrier ◽  
Resistant Strains ◽  
Single Point Mutations ◽  
The Impact ◽  
Retroviral Recombination

Retroviral recombination is a potential mechanism for the development of multiply drug resistant viral strains but the impact on the clinical outcomes of antiretroviral therapy in HIV-infected patients is unclear. Recombination can favour resistance by combining single-point mutations into a multiply resistant genome but can also hinder resistance by breaking up associations between mutations. Previous analyses, based on population genetic models, have suggested that whether recombination is favoured or hindered depends on the fitness interactions between loci, or epistasis. In this paper, a mathematical model is developed that includes viral dynamics during therapy and shows that population dynamics interact non-trivially with population genetics. The outcome of therapy depends critically on the changes to the frequency of cell co-infection and I review the evidence available. Where recombination does have an effect on therapy, it is always to slow or even halt the emergence of multiply resistant strains. I also find that for patients newly infected with multiply resistant strains, recombination can act to prevent reversion to wild-type virus. The analysis suggests that treatment targeted at multiple parts of the viral life-cycle may be less prone to drug resistance due to the genetic barrier caused by recombination but that, once selected, mutants resistant to such regimens may be better able to persist in the population.

scholarly journals Emergence of Reduced Susceptibility and Resistance to Fluoroquinolones in Escherichia coliin Taiwan and Contributions of Distinct Selective Pressures

2001 ◽  
Vol 45 (11) ◽  
pp. 3084-3091 ◽  
Author(s):  
L. Clifford McDonald ◽  
Feng-Jui Chen ◽  
Hsiu-Jung Lo ◽  
Hsiao-Chuan Yin ◽  
Po-Liang Lu ◽  
...  
Keyword(s):  
Single Point ◽  
Point Mutations ◽  
E Coli ◽  
Hospital Acquired Infections ◽  
Selective Pressures ◽  
Adult Inpatient ◽  
Resistant Strains ◽  
Single Point Mutations ◽  
Hospital Acquired ◽  
Susceptibility And Resistance

ABSTRACT A survey of 1,203 Escherichia coli isolates from 44 hospitals in Taiwan revealed that 136 (11.3%) isolates were resistant to fluoroquinolones and that another 261 (21.7%) isolates had reduced susceptibility. Resistance was more common in isolates responsible for hospital-acquired (mostly in intensive care units) infections (17.5%) than in other adult inpatient (11.4%; P = 0.08) and outpatient isolates (11.9%; P > 0.1). Similarly, reduced susceptibility was more common in isolates responsible for hospital-acquired infections (30.9%) than in other adult inpatient (21.0%; P = 0.04) and outpatient (21.4%; P = 0.06) isolates. Isolates from pediatric patients were less likely to be resistant (1.3 versus 12.0%; P < 0.01) but were nearly as likely to have reduced susceptibility (17.7 versus 21.9%;P > 0.1) as nonpediatric isolates. There was an inverse relationship in the proportion of isolates that were resistant versus the proportion that had reduced susceptibility among isolates from individual hospitals (R = 0.031; P < 0.05). In an analysis of isolates from two hospitals, all 9 resistant strains possessed double point mutations ingyrA and all 19 strains with reduced susceptibility strains had single point mutations; no mutations were found among fully susceptible strains. Risk factors for resistance included underlying cancer (odds ratio [OR], 83; 95% confidence interval [CI95], 7.3 to 2,241; P < 0.001), exposure to a quinolone (OR, undefined; P = 0.02), and exposure to a nonquinolone antibiotic (OR, 20; CI95, 2.2 to 482; P < 0.001); underlying cancer was the only independent risk factor (OR, 83; CI95, 8.6 to 807; P < 0.001). There were no significant associations between any of these factors and reduced susceptibility. Whereas acute and chronic quinolone use in cancer patients is a major selective pressure for resistance, other undetermined but distinct selective pressures appear to be more responsible for reduced susceptibility to fluoroquinolones in E. coli.

scholarly journals Quinolone-resistant mutants of escherichia coli DNA topoisomerase IV parC gene.

1996 ◽  
Vol 40 (3) ◽  
pp. 710-714 ◽  
Author(s):  
Y Kumagai ◽  
J I Kato ◽  
K Hoshino ◽  
T Akasaka ◽  
K Sato ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Dna Gyrase ◽  
Mutant Gene ◽  
Missense Mutations ◽  
Topoisomerase Iv ◽  
Dna Topoisomerase ◽  
E Coli ◽  
A Subunit ◽  
Resistant Strains ◽  
Mutant Genes

Escherichia coli quinolone-resistant strains with mutations of the parC gene, which codes for a subunit of topoisomerase IV, were isolated from a quinolone-resistant gyrA mutant of DNA gyrase. Quinolone-resistant parC mutants were also identified among the quinolone-resistant clinical strains. The parC mutants became susceptible to quinolones by introduction of a parC+ plasmid. Introduction of the multicopy plasmids carrying the quinolone-resistant parC mutant gene resulted in an increase in MICs of quinolones for the parC+ and quinolone-resistant gyrA strain. Nucleotide sequences of the quinolone-resistant parC mutant genes were determined, and missense mutations at position Gly-78, Ser-80, or Glu-84, corresponding to those in the quinolone-resistance-determining region of DNA gyrase, were identified. These results indicate that topoisomerase IV is a target of quinolones in E. coli and suggest that the susceptibility of E. coli cells to quinolones is determined by sensitivity of the targets, DNA gyrase and topoisomerase IV.

scholarly journals First Characterization of Fluoroquinolone Resistance in Streptococcus suis

2006 ◽  
Vol 51 (2) ◽  
pp. 777-782 ◽  
Author(s):  
Jose Antonio Escudero ◽  
Alvaro San Millan ◽  
Ana Catalan ◽  
Adela G. de la Campa ◽  
Estefania Rivero ◽  
...  
Keyword(s):  
Horizontal Gene Transfer ◽  
Single Point ◽  
Point Mutations ◽  
Streptococcus Suis ◽  
Fluoroquinolone Resistance ◽  
Genes Encoding ◽  
Resistant Strains ◽  
Single Point Mutations ◽  
Clonal Spread

ABSTRACT We have identified and sequenced the genes encoding the quinolone-resistance determining region (QRDR) of ParC and GyrA in fluoroquinolone-susceptible and -resistant Streptococcus suis clinical isolates. Resistance is the consequence of single point mutations in the QRDRs of ParC and GyrA and is not due to clonal spread of resistant strains or horizontal gene transfer with other bacteria.

scholarly journals Structural elements within the methylation loop (residues 112–117) and EF hands III and IV of calmodulin are required for Lys115 trimethylation

1999 ◽  
Vol 340 (2) ◽  
pp. 417-424 ◽  
Author(s):  
Jennifer A. COBB ◽  
Chang-Hoon HAN ◽  
David M. WILLS ◽  
Daniel M. ROBERTS
Keyword(s):  
Single Point ◽  
Point Mutations ◽  
Site Directed Mutagenesis ◽  
Structural Elements ◽  
Nad Kinase ◽  
Wild Type ◽  
Loop Sequence ◽  
Ef Hand ◽  
Single Point Mutations ◽  
Ef Hands

Calmodulin is trimethylated by a specific methyltransferase on Lys115, a residue located in a six amino acid loop (LGEKLT) between EF hands III and IV. To investigate the structural requirements for methylation, domain exchange mutants as well as single point mutations of conserved methylation loop residues (E114A, Glu114 → Ala; L116T, Leu116 → Thr) were generated. E114A and L116T activated cyclic nucleotide phosphodiesterase (PDE) and NAD+ kinase (NADK) similar to wild-type calmodulin, but lost their ability to be methylated. Domain exchange mutants in which EF hand III or IV was replaced by EF hand I or II respectively (CaM1214 and CaM1232 respectively) showed a modest effect on PDE and NADK activation (50 to 100% of wild-type), but calmodulin methylation was abolished. A third domain exchange mutant, CaMEKL, has the methylation loop sequence placed at a symmetrical position between EF hands I and II in the N-terminal lobe [residues QNP(41-43) replaced by EKL]. CaMEKL activated PDE normally, but did not activate NADK. However, CaMEKL retained the ability to bind to NADK and inhibited activation by wild-type calmodulin. Site-directed mutagenesis of single residues showed that Gln41 and Pro43 substitutions had the strongest effect on NADK activation. Additionally, CaMEKL was not methylated, suggesting that the introduction of the methylation loop between EF hands I and II is not adequate for methyltransferase recognition. Overall the data indicate that residues in the methylation loop are essential but not sufficient for methyltransferase recognition, and that additional residues unique to EF hands III and IV are required. Secondly, the QNP sequence in the loop between EF hands I and II is necessary for NADK activation.

scholarly journals Modulation of the Mechanisms Driving Transthyretin Amyloidosis

2020 ◽  
Vol 13 ◽  
Author(s):  
Filipa Bezerra ◽  
Maria João Saraiva ◽  
Maria Rosário Almeida
Keyword(s):  
Amyloid Fibrils ◽  
Single Point ◽  
Point Mutations ◽  
Disease Process ◽  
Wild Type ◽  
Transthyretin Amyloidosis ◽  
Natural Ligand ◽  
Single Point Mutations ◽  
Pharmacologic Agents ◽  
Plasma Stabilization

Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T4). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

scholarly journals Dinitroanilines Bind α-Tubulin to Disrupt Microtubules

2004 ◽  
Vol 15 (4) ◽  
pp. 1960-1968 ◽  
Author(s):  
Naomi S. Morrissette ◽  
Arpita Mitra ◽  
David Sept ◽  
L. David Sibley
Keyword(s):  
Bos Taurus ◽  
Single Point ◽  
Point Mutations ◽  
Docking Studies ◽  
Chemical Mutagenesis ◽  
Wild Type ◽  
Protozoan Parasites ◽  
Resistant Lines ◽  
Single Point Mutations ◽  
A Site

Protozoan parasites are remarkably sensitive to dinitroanilines such as oryzalin, which disrupt plant but not animal microtubules. To explore the basis of dinitroaniline action, we isolated 49 independent resistant Toxoplasma gondii lines after chemical mutagenesis. All 23 of the lines that we examined harbored single point mutations in α-tubulin. These point mutations were sufficient to confer resistance when transfected into wild-type parasites. Several mutations were in the M or N loops, which coordinate protofilament interactions in the microtubule, but most of the mutations were in the core of α-tubulin. Docking studies predict that oryzalin binds with an average affinity of 23 nM to a site located beneath the N loop of Toxoplasma α-tubulin. This binding site included residues that were mutated in several resistant lines. Moreover, parallel analysis of Bos taurus α-tubulin indicated that oryzalin did not interact with this site and had a significantly decreased, nonspecific affinity for vertebrate α-tubulin. We propose that the dinitroanilines act through a novel mechanism, by disrupting M-N loop contacts. These compounds also represent the first class of drugs that act on α-tubulin function.

scholarly journals An isolated CLASP TOG domain suppresses microtubule catastrophe and promotes rescue

2018 ◽  
Vol 29 (11) ◽  
pp. 1359-1375 ◽  
Author(s):  
Shreoshi Majumdar ◽  
Tae Kim ◽  
Zhe Chen ◽  
Sarah Munyoki ◽  
Shih-Chia Tso ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Single Point ◽  
Point Mutations ◽  
Regulatory Activity ◽  
Binding Properties ◽  
Binding Surface ◽  
Tubulin Binding ◽  
Single Point Mutations ◽  
Insight Into

Microtubules are heavily regulated dynamic polymers of αβ-tubulin that are required for proper chromosome segregation and organization of the cytoplasm. Polymerases in the XMAP215 family use arrayed TOG domains to promote faster microtubule elongation. Regulatory factors in the cytoplasmic linker associated protein (CLASP) family that reduce catastrophe and/or increase rescue also contain arrayed TOGs, but how CLASP TOGs contribute to activity is poorly understood. Here, using Saccharomyces cerevisiae Stu1 as a model CLASP, we report structural, biochemical, and reconstitution studies that clarify functional properties of CLASP TOGs. The two TOGs in Stu1 have very different tubulin-binding properties: TOG2 binds to both unpolymerized and polymerized tubulin, and TOG1 binds very weakly to either. The structure of Stu1-TOG2 reveals a CLASP-specific residue that likely confers distinctive tubulin-binding properties. The isolated TOG2 domain strongly suppresses microtubule catastrophe and increases microtubule rescue in vitro, contradicting the expectation that regulatory activity requires an array of TOGs. Single point mutations on the tubulin-binding surface of TOG2 ablate its anti-catastrophe and rescue activity in vitro, and Stu1 function in cells. Revealing that an isolated CLASP TOG can regulate polymerization dynamics without being part of an array provides insight into the mechanism of CLASPs and diversifies the understanding of TOG function.

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