Insights into SOD1-linked amyotrophic lateral sclerosis from NMR studies of Ni2+- and other metal-ion-substituted wild-type copper–zinc superoxide dismutases

The dimeric copper-zinc superoxide dismutase Cu(2)Zn(2)SOD1 is a particularly interesting system for biological inorganic chemical studies because substitutions of the native Cu and/or Zn ions by a non-native metal ion cause minimal structural changes and result in high enzymatic activity for those derivatives with Cu remained in the Cu site. The pioneering NMR studies by Ivano Bertini and coworkers of the magnetically coupled derivative Cu(2)Co(2)SOD1 are of particular importance in this regard. In addition to Co(2+), Ni(2+) is also a versatile metal ion for substitution into Cu(2)Zn(2)SOD1, showing very little disturbance of the structure in Cu(2)Ni(2)SOD1 and a very good mimic of the native Cu ion in Ni(2)Zn(2)SOD1. The NMR studies presented here were inspired by and indebted to Professor Bertini's paramagnetic NMR pursuits of metalloproteins. In the current study, we report Ni(2+) binding to apo-wild type SOD1 and a time-dependent Ni(2+) ion migration from the Zn site to the Cu site and preparation and characterization of Ni(2)Ni(2)SOD1, which shows similar coordination properties to those of Cu(2)Cu(2)SOD1, namely a different anion binding property from the wild type and a possibly broken bridging His. Mutations in the human SOD1 gene can cause familial amyotrophic lateral sclerosis (ALS), and mutant SOD1 proteins with significantly altered metal binding behaviors are implicated in causing the disease. We therefore conclude by discussing the effects of the ALS mutations on the remarkable stabilities and metal-binding properties of wild type SOD1 proteins and the implications concerning the causes of SOD1-linked ALS