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Structural basis for transcription inhibition by tagetitoxin
Dmitry G Vassylyev1, Vladimir Svetlov, Marina N Vassylyeva
1Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama 35294, USA. dmitry@uab.edu
Nature Structural & Molecular Biology
|November 8, 2005
Summary
Tagetitoxin inhibits bacterial transcription by binding to RNA polymerase. A structural study reveals it coordinates a magnesium ion, stabilizing an inactive transcription intermediate and blocking RNA synthesis.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Tagetitoxin (Tgt) is a known inhibitor of bacterial transcription, but its mechanism of action remains elusive.
- RNA polymerase (RNAP) is the central enzyme responsible for transcription, and its regulation is crucial for cellular processes.
Purpose of the Study:
- To elucidate the structural basis and mechanism of Tagetitoxin inhibition of bacterial RNA polymerase.
- To understand how Tgt interacts with RNAP and affects its catalytic activity.
Main Methods:
- X-ray crystallography was used to determine the structure of the Thermus thermophilus RNAP-Tgt complex at 2.4 A resolution.
- Biochemical assays were performed to assess Tgt inhibition and identify resistant mutations.
Main Results:
- The Tgt-binding site overlaps with the ppGpp binding site, offering partial protection against inhibition.
- Tgt binding involves polar interactions with specific RNAP beta and beta' residues.
- A Tgt-bound magnesium ion, distinct from catalytic ions, is coordinated by Tgt and active site residues.
- Tgt inhibits all RNAP catalytic reactions, proposing a mechanism involving stabilization of an inactive transcription intermediate.
Conclusions:
- Tagetitoxin inhibits transcription by coordinating a magnesium ion that stabilizes an inactive RNAP intermediate.
- Metal ion-mediated remodeling of the active site may be a general mechanism for regulating nucleic acid enzymes.