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Structural basis for allosteric substrate specificity regulation in anaerobic ribonucleotide reductases
K M Larsson1, J Andersson, B M Sjöberg
1Department of Biochemistry and Biophysics, Stockholm University, S-106 91, Stockholm, Sweden.
Structure (London, England : 1993)
|October 6, 2001
Summary
Ribonucleotide reductases (RNRs) use deoxyribonucleoside triphosphates (dNTPs) to control substrate specificity. Structural analysis reveals how subtle effector binding triggers significant conformational changes in the active site, impacting enzyme function.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Ribonucleotide reductases (RNRs) exhibit substrate specificity determined by deoxyribonucleoside triphosphates (dNTPs) binding to an allosteric site.
- Previous studies suggested common evolutionary origins for RNR classes based on allosteric regulation kinetics.
- Recent structural data support divergent evolution, but the mechanism of allosteric signal transmission remains unclear.
Purpose of the Study:
- To investigate the structural basis of allosteric signal transmission in class III anaerobic RNR.
- To compare the conformational effects of different dNTP effectors on RNR structure.
- To elucidate how effector binding influences active site conformation and enzyme specificity.
Main Methods:
- X-ray crystallography of class III anaerobic RNR in complex with four dNTPs.
- Comparative structural analysis of protein conformations.
- Identification of key amino acid residues involved in effector discrimination.
Main Results:
- Structural determination of class III anaerobic RNR complexes with four dNTPs.
- Identification of Gln-114 and Glu-181 as critical for effector discrimination.
- Observation of significant conformational changes in the active site loop (loop 2), including Phe-194, upon effector binding.
- Distinct conformational differences between purine and pyrimidine effector binding, with subtle variations within the purine group.
Conclusions:
- Subtle differences in effector base size and hydrogen bonding are transmitted to major active site conformational changes.
- The altered overlap of Phe-194 with the substrate base likely dictates active site hydrogen bonding patterns.
- The findings provide insights into the evolutionary divergence of RNRs and the mechanism of allosteric regulation.
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