| Research Abstract |
Amyotrophic lateral sclerosis (ALS) is a degenerative disorder of motor neurons of cortex, brainstem, and spinal cord. About 10% of all ALS are familial cases, which are inherited as an autosomal dominant trait. Recent studies showed that about 20% of familial ALS (FALS) cases have mutations in SOD1, the gene for Cu, Zn-superoxide dismutase (SOD) that catalyzes the dismutation of superoxide radical anions to hydrogen peroxide and oxygen molecules. All of the FALS mutations do not change any active site residues involving the coordination of the metal ions or residues forming the electrostatic active channel. Rather, most of the FALS mutant sites alter conserved interactions critical to the subunit fold and dimer contact.
The mutant SOD associated with FALS found in Sanin area north western part of Japan was derived from 2 bp deletion in the SOD1. The SOD activity in extracts from red blood cells, brain tissues, and lymphoblastoid cells revealed an about 50% reduction in FALS patients co
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mpared to normal individuals. The human SOD1 was expressed as a fusion protein in Eschericia coli, then purified by an affinity chromatography. The SOD activity and protein band clearly demonstrated even in the fused states. But, the fused protein expressed from the mutant SOD1 showed clear but very low activity, After the separation of mutant SOD from the fused protein by Factor Xa, the activity and the protein band on the gel disappeared during the purification process. As the 2 bp deletion was found to be very important, by analyzing the three dimensional modeL structure, to compose the dimeric active structure, The dimer structure of the mutant SOD is very labile, thus copper ions released from the SOD molecules will be the source of oxidative stress in tissues of patients. Although the association mechanism of the mutations of SOD with FALS is still unknown, the lowered SOD activity may not be associated FALS but the SOD mutants retain high levels of peroxidative activity (the gain-of-function), and utilize its own dismutation product producing the main species hydroxyl radicals which is the source of oxidative stress. Less
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