title: Cu,Zn-superoxide dismutase increases toxicity of mutant and zinc-deficient superoxide dismutase by enhancing protein stability.
abstract: When replete with zinc and copper, amyotrophic lateral sclerosis (ALS)-associated mutant SOD proteins can protect motor neurons in culture from trophic factor deprivation as efficiently as wild-type SOD. However, the removal of zinc from either mutant or wild-type SOD results in apoptosis of motor neurons through a copper- and peroxynitrite-dependent mechanism. It has also been shown that motor neurons isolated from transgenic mice expressing mutant SODs survive well in culture but undergo apoptosis when exposed to nitric oxide via a Fas-dependent mechanism. We combined these two parallel approaches for understanding SOD toxicity in ALS and found that zinc-deficient SOD-induced motor neuron death required Fas activation, whereas the nitric oxide-dependent death of G93A SOD-expressing motor neurons required copper and involved peroxynitrite formation. Surprisingly, motor neuron death doubled when Cu,Zn-SOD protein was either delivered intracellularly to G93A SOD-expressing motor neurons or co-delivered with zinc-deficient SOD to nontransgenic motor neurons. These results could be rationalized by biophysical data showing that heterodimer formation of Cu,Zn-SOD with zinc-deficient SOD prevented the monomerization and subsequent aggregation of zinc-deficient SOD under thiol-reducing conditions. ALS mutant SOD was also stabilized by mutating cysteine 111 to serine, which greatly increased the toxicity of zinc-deficient SOD. Thus, stabilization of ALS mutant SOD by two different approaches augmented its toxicity to motor neurons. Taken together, these results are consistent with copper-containing zinc-deficient SOD being the elusive "partially unfolded intermediate" responsible for the toxic gain of function conferred by ALS mutant SOD.
authors.affiliation: Burke Medical Research Institute, White Plains, New York 10605, USA.
authors.forename: Mary Anne
authors.initials: MA
authors.lastname: Garner
authors.forename: Karina C
authors.initials: KC
authors.lastname: Ricart
authors.forename: Blaine R
authors.initials: BR
authors.lastname: Roberts
authors.forename: Valerie C
authors.initials: VC
authors.lastname: Bomben
authors.forename: Manuela
authors.initials: M
authors.lastname: Basso
authors.forename: Yaozu
authors.initials: Y
authors.lastname: Ye
authors.forename: John
authors.initials: J
authors.lastname: Sahawneh
authors.forename: Maria Clara
authors.initials: MC
authors.lastname: Franco
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Beckman
authors.forename: Alvaro G
authors.initials: AG
authors.lastname: Estévez
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis; D002614:Chelating Agents / Q000494:pharmacology; D003300:Copper / Q000737:chemistry; D007700:Kinetics; D009046:Motor Neurons / Q000378:metabolism; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry; D030421:Peroxynitrous Acid / Q000737:chemistry; D011506:Proteins / Q000737:chemistry; D051381:Rats; D013482:Superoxide Dismutase / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; D011506:Proteins; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D003300:Copper; D013482:Superoxide Dismutase