Ribonucleotide Reductase: Difference between revisions

The structure of ribonucleotide reductase is composed of two components. One portion is the radical generator which produces and stores the radical. This portion is used to oxidize the substrate to its radical form which is the first step of the overall reaction. The second portion of the structure consists of a reductase. The reductase is the same for all three classes, but the radical generator differs. <ref name="structure">DOI:10.1016/S0079-6107(01)00014-1</ref> Class I ribonucleotide reductase produces the stable radical, <scene name='91/910568/Iron_center/2'>tyrosyl</scene>, through the dinuclear <scene name='91/910568/Iron_center/1'>iron center</scene> of the subunit. The three different classes of this enzyme have a cysteine residue that is located at the protein loop of the active site. Class II enzymes differ in which it uses cobalamin as a cofactor for the radical. The protein loop is in the center of the alpha, beta-barrel of the structural motif. The cysteine residue is conserved until it is converted to a thiyl radical. The conversion to the thiyl radical is needed to initiate substrate turnover. The different classes of RNR are different but do show some similarities which suggest that they all evolved from one common reductase. <ref name="pubmed">DOI:10.1016/j.bbapap.2004.02.007</ref> Class III of RNR is comprised of two proteins that require an iron-sulfur center.