| Abstract
| - The backbone assignment of reduced human dimeric Cu,Zn superoxide dismutase (SOD) wasperformed on a sample 100% enriched in 15N, 13C and 70% enriched in 2H. 15N T1, T2, and T1ρ and15N-1H NOE assignment was performed at 600 MHz proton frequency on both wild-type SOD and themonomeric F50E/G51E/E133Q mutant. This allowed a comparison of the mobility in the subnanosecondand in the millisecond to microsecond time scales of the two systems. Both proteins are rather rigid,although some breathing of the β sheets is detected in the wild type dimer. The monomer displays largemobility in the loops in the first part of the sequence, in loop IVa where point mutations have beenintroduced and at the C-terminus. The dimeric wild type is rigidified at loop IVa and at the C-terminus.Only loop VII shows a higher mobility in the dimer (besides some individual NH moieties). Conformationalequilibria are displayed in the monomeric form around cysteines 57 and 146, thus explaining the disorderof arginine 143 which is the most important residue in guiding O2- toward the copper ion. The largermobility in the wild type form with respect to the monomer in the picosecond to nanosecond time scaleof helix α1 and loop VIIb, which provides the correct electrostatic driving force for O2- in the activechannel, has been discussed in terms of favoring the activity of SOD.
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