PARAMAGNETIC RELAXATION AS A TOOL FOR SOLUTION STRUCTURE DETERMINATION - CLOSTRIDIUM-PASTEURIANUM FERREDOXIN AS AN EXAMPLE

The possibility of using the relaxation properties of nuclei for solut ion structure determination of paramagnetic metalloproteins is critica lly evaluated, First of all, it is theoretically and experimentally de monstrated that magnetization recovery in nonselective inversion recov ery experiments can be approximated to an exponential in both diamagne tic and paramagnetic systems. This permits the estimate of the contrib ution of paramagnetic relaxation when dominant or sizable, Then, it is shown that the averaging of paramagnetic relaxation rates due to cros s relaxation is often tolerably small with respect to the use of param agnetic relaxation rates as constraints for structural determination. Finally, a protocol is proposed to use such paramagnetic relaxation ra tes, which depend on the sixth power of the metal to resonating nucleu s distance, as constraints for solution structure determination of pro teins. As an example, the available solution structure of the oxidized ferredoxin from Clostridium pasteurianum has been significantly impro ved in resolution especially in the proximity of the metal ions by usi ng 69 new constraints based on paramagnetic relaxation. (C) 1997 Wiley -Liss, Inc.