Spectroscopic Evidence for a H Bond Network at Y356 Located at the Subunit Interface of Active E. coli Ribonucleotide Reductase.
Biochemistry
; 56(28): 3647-3656, 2017 07 18.
Article
em En
| MEDLINE
| ID: mdl-28640584
ABSTRACT
The reaction catalyzed by E. coli ribonucleotide reductase (RNR) composed of α and ß subunits that form an active α2ß2 complex is a paradigm for proton-coupled electron transfer (PCET) processes in biological transformations. ß2 contains the diferric tyrosyl radical (Y122·) cofactor that initiates radical transfer (RT) over 35 Å via a specific pathway of amino acids (Y122· â [W48] â Y356 in ß2 to Y731 â Y730 â C439 in α2). Experimental evidence exists for colinear and orthogonal PCET in α2 and ß2, respectively. No mechanistic model yet exists for the PCET across the subunit (α/ß) interface. Here, we report unique EPR spectroscopic features of Y356·-ß, the pathway intermediate generated by the reaction of 2,3,5-F3Y122·-ß2/CDP/ATP with wt-α2, Y731F-α2, or Y730F-α2. High field EPR (94 and 263 GHz) reveals a dramatically perturbed g tensor. [1H] and [2H]-ENDOR reveal two exchangeable H bonds to Y356· a moderate one almost in-plane with the π-system and a weak one. DFT calculation on small models of Y· indicates that two in-plane, moderate H bonds (rO-H â¼1.8-1.9 Å) are required to reproduce the gx value of Y356· (wt-α2). The results are consistent with a model, in which a cluster of two, almost symmetrically oriented, water molecules provide the two moderate H bonds to Y356· that likely form a hydrogen bond network of water molecules involved in either the reversible PCET across the subunit interface or in H+ release to the solvent during Y356 oxidation.
Texto completo:
1
Coleções:
01-internacional
Contexto em Saúde:
3_ND
Base de dados:
MEDLINE
Assunto principal:
Ribonucleotídeo Redutases
/
Escherichia coli
Idioma:
En
Revista:
Biochemistry
Ano de publicação:
2017
Tipo de documento:
Article