Decreased zinc affinity of amyotrophic lateral sclerosis-associated superoxide dismutase mutants leads to enhanced catalysis of tyrosine nitration by peroxynitrite.
Mutations to Cu/Zn superoxide dismutase (SOD) linked to familial amyotrophic lateral sclerosis (ALS) enhance an unknown toxic reaction that leads to the selective degeneration of motor neurons. However, the question of how >50 different missense mutations produce a common toxic phenotype remains perplexing. We found that the zinc affinity of four ALS-associated SOD mutants was decreased up to 30-fold compared to wild-type SOD but that both mutants and wild-type SOD retained copper with similar affinity. Neurofilament-L (NF-L), one of the most abundant proteins in motor neurons, bound multiple zinc atoms with sufficient affinity to potentially remove zinc from both wild-type and mutant SOD while having a lower affinity for copper. The loss of zinc from wild-type SOD approximately doubled its efficiency for catalyzing peroxynitrite-mediated tyrosine nitration, suggesting that one gained function by SOD in ALS may be an indirect consequence of zinc loss. Nitration of protein-bound tyrosines is a permanent modification that can adversely affect protein function. Thus, the toxicity of ALS-associated SOD mutants may be related to enhanced catalysis of protein nitration subsequent to zinc loss. By acting as a high-capacity zinc sink, NF-L could foster the formation of zinc-deficient SOD within motor neurons.
Crow
J P
JP
Department of Anesthesiology, University of Alabama at Birmingham, 35233, U.S.A.
Sampson
J B
JB
Zhuang
Y
Y
Thompson
J A
JA
Beckman
J S
JS
D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D003001:Cloning, Molecular; D006801:Humans; D007700:Kinetics; D008099:Liver; D008668:Metallothionein / Q000378:metabolism; D008961:Models, Structural; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D011487:Protein Conformation; D011817:Rabbits; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D009566:Nitrates; D011994:Recombinant Proteins; C039642:peroxynitric acid; D014443:Tyrosine; D008668:Metallothionein; D013482:Superoxide Dismutase; D015032:Zinc