A COMPLETE RELAXATION MATRIX REFINEMENT OF THE SOLUTION STRUCTURE OF A PARAMAGNETIC METALLOPROTEIN - REDUCED HIPIP-I FROM ECTOTHIORHODOSPIRA-HALOPHILA

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.