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Assignment of backbone NMR resonances and secondary structural elements of a reduced monomeric mutant of copper/zinc superoxide dismutase

An extensive series of three‐dimensional, triple resonance experiments were performed on a fully labeled 13C, 15N monomeric form of human copper/zinc superoxide dismutase which contains 153 amino acids. The present system, in addition to the mutations at the subunit–subunit interface (Phe50→Glu, Gly51→Glu) which lead to the monomeric form, carries the mutation of the Glu133 to Gln, a residue at the active channel entrance. Firm assignment was found for 97% of the protons, 99% of the 13Cα, 91% of the 15N, 98% of 13C(O) and 90% of the 13Cβ backbone resonances. Analysis of the chemical shift values of 13Cα, Hα, 13Cβ and 13CO, of 3JHNHα coupling constants, of NOEs between backbone protons and of the H–D exchange behavior of amide protons permits the unequivocal detection of elements of secondary structure. The secondary structure of the present monomeric form is very similar to that of the WT enzyme, although the enzymatic activity is 20% of that of the WT protein. © 1997 John Wiley & Sons, Ltd.