I. Bertini et al., A COMPLETE RELAXATION MATRIX REFINEMENT OF THE SOLUTION STRUCTURE OF A PARAMAGNETIC METALLOPROTEIN - REDUCED HIPIP-I FROM ECTOTHIORHODOSPIRA-HALOPHILA, Proteins, 24(2), 1996, pp. 158-164
We have accounted for the effect of paramagnetism on the intensities o
f NOEs in a 73-residue paramagnetic metalloprotein, the reduced high-p
otential iron sulfur protein ISO I from Ectothiorhodospira halophila,
whose solution structure had been recently solved by us. The paramagne
tic effects were dealt with through a suitably modified complete relax
ation matrix approach. We have then recalculated the structure through
a distance geometry program by minimizing the difference between the
sixth roots of the calculated and experimental NOEs. The average RMSD,
calculated on residues 4-71, within the structures constituting the t
wo families decreased from 0.67 to 0.46 Angstrom for backbone atoms an
d from 1.23 to 1.06 Angstrom for all heavy atoms. The structures in th
e new family are for the most part within the indetermination of the p
revious, less resolved, family. A few specific differences are detecte
d and related to the presence of non-negligible paramagnetic effects,
which are now properly evaluated. (C) 1996 Wiley-Liss, Inc.