TY - JOUR
T1 - Electronic structural flexibility of heterobimetallic Mn/Fe cofactors
T2 - R2lox and R2c proteins
AU - Shafaat, Hannah S.
AU - Griese, Julia J.
AU - Pantazis, Dimitrios A.
AU - Roos, Katarina
AU - Andersson, Charlotta S.
AU - Popović-Bijelić, Ana
AU - Gräslund, Astrid
AU - Siegbahn, Per E.M.
AU - Neese, Frank
AU - Lubitz, Wolfgang
AU - Högbom, Martin
AU - Cox, Nicholas
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/9/24
Y1 - 2014/9/24
N2 - The electronic structure of the Mn/Fe cofactor identified in a new class of oxidases (R2lox) described by Andersson and Hö gbom [Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 5633] is reported. The R2lox protein is homologous to the small subunit of class Ic ribonucleotide reductase (R2c) but has a completely different in vivo function. Using multifrequency EPR and related pulse techniques, it is shown that the cofactor of R2lox represents an antiferromagnetically coupled MnIII/ FeIII dimer linked by a μ-hydroxo/bis-μ-carboxylato bridging network. The MnIII ion is coordinated by a single water ligand. The R2lox cofactor is photoactive, converting into a second form ( R2lox Photo) upon visible illumination at cryogenic temperatures (77 K) that completely decays upon warming. This second, unstable form of the cofactor more closely resembles the MnIII/FeIII cofactor seen in R2c. It is shown that the two forms of the R2lox cofactor differ primarily in terms of the local site geometry and electronic state of the MnIII ion, as best evidenced by a reorientation of its unique 55Mn hyperfine axis. Analysis of the metal hyperfine tensors in combination with density functional theory (DFT) calculations suggests that this change is triggered by deprotonation of the μ-hydroxo bridge. These results have important consequences for the mixed-metal R2c cofactor and the divergent chemistry R2lox and R2c perform.
AB - The electronic structure of the Mn/Fe cofactor identified in a new class of oxidases (R2lox) described by Andersson and Hö gbom [Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 5633] is reported. The R2lox protein is homologous to the small subunit of class Ic ribonucleotide reductase (R2c) but has a completely different in vivo function. Using multifrequency EPR and related pulse techniques, it is shown that the cofactor of R2lox represents an antiferromagnetically coupled MnIII/ FeIII dimer linked by a μ-hydroxo/bis-μ-carboxylato bridging network. The MnIII ion is coordinated by a single water ligand. The R2lox cofactor is photoactive, converting into a second form ( R2lox Photo) upon visible illumination at cryogenic temperatures (77 K) that completely decays upon warming. This second, unstable form of the cofactor more closely resembles the MnIII/FeIII cofactor seen in R2c. It is shown that the two forms of the R2lox cofactor differ primarily in terms of the local site geometry and electronic state of the MnIII ion, as best evidenced by a reorientation of its unique 55Mn hyperfine axis. Analysis of the metal hyperfine tensors in combination with density functional theory (DFT) calculations suggests that this change is triggered by deprotonation of the μ-hydroxo bridge. These results have important consequences for the mixed-metal R2c cofactor and the divergent chemistry R2lox and R2c perform.
UR - http://www.scopus.com/inward/record.url?scp=84924692311&partnerID=8YFLogxK
U2 - 10.1021/ja507435t
DO - 10.1021/ja507435t
M3 - Article
SN - 0002-7863
VL - 136
SP - 13399
EP - 13409
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 38
ER -