The Active Form of Chlamydia trachomatis Ribonucleotide Reductase R2 Protein Contains a Heterodinuclear Mn(Ⅳ)/Fe(Ⅲ) Cluster with S = 1 Ground State

摘要

The reduction of nucleotides to 2'-deoxynucleotides by ribonucleotide reductases (RNRs) begins with the abstraction of the 3'-hydrogen atom of the substrate by a transient cysteine thiyl radical (C~·). Class Ⅰ, Ⅱ, and Ⅲ RNRs differ in subunit composition and the nature of the cofactor used to generate the 3'-H-abstracting C~·. A conventional class Ⅰ RNR uses a stable tyrosyl radical (Y~·), which is introduced into the enzyme's homodimeric R2 subunit (also denoted β_2) by reaction of O_2 with an adjacent carboxylate-bridged non-heme diiron cluster, to generate the C~· in its R1 subunit (also denoted α_2) via long-range (～35 A) proton-coupled electron transfer (PCET).