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Ribonucleotide reductase--structural studies of a radical enzyme
H Eklund1, M Eriksson, U Uhlin
1Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, Sweden.
Biological Chemistry
|August 1, 1997
Summary
Ribonucleotide reductase uses a stable organic free radical on its R2 subunit to facilitate substrate processing in the R1 subunit. A radical transfer pathway connects these subunits, enabling essential enzymatic activity for DNA synthesis.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Ribonucleotide reductase (R2) is crucial for DNA synthesis.
- It possesses a stable organic free radical on a tyrosine residue in the R2 subunit.
- The catalytic site resides in the R1 subunit, necessitating a radical transfer mechanism.
Purpose of the Study:
- To elucidate the radical transfer pathway in ribonucleotide reductase.
- To understand the structural basis for radical delivery from R2 to R1.
- To investigate the active site architecture and its role in substrate processing.
Main Methods:
- The study likely involved structural analysis (e.g., X-ray crystallography) to determine the protein structure.
- Biochemical assays may have been used to probe radical transfer and enzyme activity.
- Computational modeling could have been employed to study the radical transfer pathway.
Main Results:
- A long-range, protein-mediated pathway facilitates radical transfer from R2 to R1.
- The active site in R1 features a beta/alpha-barrel structure.
- A hydrogen-bonded system connects the protein surface to Cys439 at the active site.
Conclusions:
- The identified pathway is essential for ribonucleotide reductase activity.
- Cys439 is strategically positioned to initiate substrate processing by abstracting a hydrogen atom.
- The enzyme's structure supports efficient radical delivery and catalysis for nucleotide reduction.