Structure and function of the radical enzyme ribonucleotide reductase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Ribonucleotide reductases (RNRs) are vital enzymes responsible for synthesizing deoxyribonucleotides, the building blocks of DNA.
• RNRs achieve this by reducing ribonucleotides, a process involving radical chemistry that differs across enzyme classes.
• Three main classes of RNRs exist, distinguished by their radical generation mechanisms: Class I (iron-dependent), Class II (cobalamin-dependent), and Class III (glycyl radical-dependent).

Purpose of the Study:

• To elucidate the diverse radical generation mechanisms employed by different classes of Ribonucleotide reductases.
• To highlight the common structural features and radical initiation steps across RNR classes.
• To review recent structural and functional insights into Class I and Class III RNRs and their allosteric regulation.

Main Methods:

• Comparative analysis of structural and functional data from various RNR classes.
• Review of existing literature on enzyme mechanisms and radical chemistry.
• Examination of allosteric regulation in RNRs.

Main Results:

• Class I RNRs use an iron center to generate a stable tyrosyl radical, while Class II and III RNRs utilize cobalamin and glycyl radicals, respectively.
• All RNR classes share a common mechanism involving a transient cysteinyl radical at the active site to initiate the reaction.
• Structural studies provide detailed insights into the radical's controlled delivery in Class I enzymes and the allosteric regulation of RNRs.

Conclusions:

• RNRs exhibit diverse yet conserved strategies for radical generation and utilization in deoxyribonucleotide synthesis.
• Structural and mechanistic understanding of RNRs is advancing, revealing sophisticated control over radical reactions and allosteric regulation.
• Further research into RNRs can provide deeper insights into DNA synthesis and cellular regulation.