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Using Modified Synthetic Oligonucleotides to Assay Nucleic Acid-Metabolizing Enzymes
Published on: July 5, 2024
Structural basis for adenosylcobalamin activation in AdoCbl-dependent ribonucleotide reductases
Karl-Magnus Larsson1, Derek T Logan, Pär Nordlund
1Department of Biochemistry and Biophysics, Stockholm University, S-106 91 Stockholm, Sweden.
ACS Chemical Biology
|August 3, 2010
Summary
Class II ribonucleotide reductases (RNR) use adenosylcobalamin (AdoCbl) to generate essential thiyl radicals. Structural analysis reveals a unique cofactor-substrate interaction, suggesting a distinct radical transfer mechanism for this enzyme class.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Class II ribonucleotide reductases (RNR) are crucial enzymes that generate thiyl radicals via adenosylcobalamin (AdoCbl) cofactor cleavage.
- The precise mechanism of accelerated Co-C bond cleavage in AdoCbl-dependent enzymes remains debated.
Purpose of the Study:
- To elucidate the structural basis for radical generation and transfer in Class II RNR.
- To investigate the role of cofactor-substrate interactions in enzyme catalysis.
Main Methods:
- X-ray crystallography of Thermotoga maritima Class II RNR in three distinct complexes.
- Structural comparison to analyze enzyme mechanism.
Main Results:
- Detailed structures reveal AdoCbl binding within the active site, shielding reactive intermediates.
- A novel direct hydrogen bond interaction between AdoCbl and the substrate phosphate group was observed.
- A conformational change in the AdoCbl ribose is necessary for hydrogen transfer.
Conclusions:
- The findings provide deep structural insights into the unique radical generation and transfer mechanism of Class II RNR.
- The observed cofactor-substrate interaction suggests a distinct catalytic strategy compared to other B12-dependent enzymes.
- Class II RNR may represent a separate mechanistic class among B12-dependent enzymes.
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