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Related Concept Videos

Structure-Activity Relationships and Drug Design01:28

Structure-Activity Relationships and Drug Design

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Drug design is a dynamic field that involves discovering and developing new medications based on specific biological targets. This process heavily relies on structure-activity relationships (SAR) and quantitative structure-activity relationships (QSAR) to guide the design and optimization of efficient drugs.
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Adrenergic Agonists: Chemistry and Structure-Activity Relationship01:16

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Adrenergic agonists' structure-activity relationship (SAR) determines their selectivity and efficacy. These agonists comprise a phenylethylamine moiety with an aromatic ring and an ethylamine side chain.
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Indirect-Acting Cholinergic Agonists: Chemistry and Structure-Activity Relationship01:29

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Indirect-acting cholinergic agonists are agents that interact with the acetylcholinesterase enzyme in the synaptic cleft, preventing the breakdown of acetylcholine into choline and acetate. Consequently, the concentration of acetylcholine in the synaptic cleft increases. These agonists can be classified into reversible and irreversible inhibitors based on their duration of action.
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Direct-Acting Cholinergic Agonists: Chemistry and Structure-Activity Relationship01:22

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Cholinergic agonists or cholinomimetics mimic the action of acetylcholine to stimulate the parasympathetic nervous system. They are categorized into direct-acting and indirect-acting agents. The direct-acting cholinergic drugs induce the parasympathetic response by directly binding to the muscarinic or nicotine receptors. In comparison, the indirect-acting cholinergic drugs prevent acetylcholine hydrolysis, indirectly contributing to the extended parasympathetic response.
The direct-acting...
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Cholinergic Antagonists: Chemistry and Structure-Activity Relationship01:29

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Cholinergic antagonists bind to cholinergic receptors and limit the effects of acetylcholine and other cholinergic agonists. Based on the specific cholinergic receptor affinity, these antagonists are classified as muscarinic or nicotinic. Anticholinergics interrupt parasympathetic innervations while sympathetic innervations remain uninterrupted. Muscarinic antagonists are also called 'muscarinic antagonists', 'antimuscarinics', or 'parasympatholytics'. Nicotinic...
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Quantitative Aspects of Drug-Receptor Interaction01:30

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The receptor occupancy theory connects a drug's response to the number of occupied receptors. With higher drug concentrations, more receptors are occupied, leading to increased responses. The formation of drug-receptor complexes involves association and dissociation rates, which reach equilibrium when the forward and backward reactions are equal. The equilibrium association constant (Ka) and its inverse, the equilibrium dissociation constant (Kd), indicate drug affinity. Higher Ka and lower...
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Updated: May 1, 2026

Quantitative Structure-Activity Relationship, Activity Prediction, and Molecular Dynamics of Non-nucleotide Reverse Transcriptase Inhibitors
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Quantitative Structure-Activity Relationship, Activity Prediction, and Molecular Dynamics of Non-nucleotide Reverse Transcriptase Inhibitors

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QnrS1 structure-activity relationships.

María M Tavío1, George A Jacoby2, David C Hooper3

  • 1Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA Microbiología, Departamento de Ciencias Clínicas, Universidad de Las Palmas de Gran Canaria, Las Palmas de G.C., España mtavio@dcc.ulpgc.es.

The Journal of Antimicrobial Chemotherapy
|April 15, 2014
PubMed
Summary
This summary is machine-generated.

Key amino acids in QnrS1 loop B significantly impact quinolone resistance and gyrase protection. Understanding these interactions is crucial for developing strategies against antibiotic resistance.

Keywords:
QnrSpentapeptide repeat proteinsquinolone resistance

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Drug Resistance

Background:

  • Quinolone resistance is a growing public health concern.
  • Qnr proteins, particularly QnrS1, play a role in mediating low-level quinolone resistance.
  • Loop B of Qnr proteins is implicated in interactions with bacterial gyrase.

Purpose of the Study:

  • To investigate the role of individual amino acids within the QnrS1 loop B in conferring quinolone resistance.
  • To assess the impact of specific QnrS1 loop B mutations on gyrase protection.
  • To elucidate the structure-function relationship between QnrS1 loop B and antibiotic resistance mechanisms.

Main Methods:

  • Site-directed alanine mutagenesis was used to create QnrS1 alleles with mutations in loop B.
  • Mutated QnrS1 proteins were expressed in Escherichia coli and purified.
  • Ciprofloxacin minimum inhibitory concentrations (MICs) were determined.
  • Gyrase supercoiling assays were performed to assess protection from ciprofloxacin.

Main Results:

  • Specific QnrS1 loop B mutations, such as Asn-110→Ala and Arg-111→Ala, significantly increased ciprofloxacin MICs.
  • Other mutations in loop B resulted in a reduced increase in ciprofloxacin MIC compared to wild-type QnrS1.
  • Mutated QnrS1 proteins showed varying degrees of protection to gyrase from ciprofloxacin action, correlating with their effect on MICs.

Conclusions:

  • Individual amino acid residues within QnrS1 loop B are critical for modulating ciprofloxacin resistance.
  • Loop B is essential for the interaction between QnrS1 and gyrase, which is necessary for quinolone resistance.
  • These findings provide insights into the molecular mechanisms of quinolone resistance mediated by Qnr proteins.