F. Demare et al., REENGINEERING THE DIIRON SITE IN RUBRERYTHRIN TOWARDS THAT IN RIBONUCLEOTIDE REDUCTASE, Inorganica Chimica Acta, 263(1-2), 1997, pp. 255-262
In order to investigate the nature and significance of the structural
differences between the diiron-oxo sites in rubrerythrin and ribonucle
otide reductase R2 protein (RNR R2), two mutant rubrerythrins, E97A an
d L60Y, were constructed, and their X-ray crystal structures determine
d. In L60Y rubrerythrin the side chain of Y60 is in a similar position
with respect to the diiron site as is Y122 in RNR R2. However, Y60 in
rubrerythrin does not make a direct hydrogen bond to an iron-coordina
ting terminal carboxylate, as does Y122 in RNR R2. This difference cou
ld partly explain why no tyrosyl radical is detected in L60Y rubreryth
rin, and why such a radical is formed and stabilized on Y122 in RNR R2
. In E97A rubrerythrin, a second histidine, H56, has become an iron li
gand, and the diiron site structure in this mutant is very similar to
that in RNR R2. The iron to which H56 coordinates has moved approximat
ely 1.6 Angstrom in E97A relative to its position in wild-type rubrery
thrin. These results suggest that one of the iron atoms in the diiron
site of rubrerythrin could alternate between coordination to H56 and E
97, thereby facilitating either intersite electron transfer or iron up
take/release. (C) 1997 Elsevier Science S.A.