not know if these aggregates are causative, harmless or even beneficial to ALS. Furthermore, the fundamental molecular mechanism by which the SOD1 mutants form aggregates is not clear.
Six years ago Siddique and Han-Xiang Deng, M.D., associate professor of neurology at the Feinberg School, started to develop and analyze various SOD1 transgenic mouse models and found, as they report in the first of the two PNAS papers, that aggregated and insoluble SOD1 is the pathogenic form that causes disease. The aggregation takes place in mitochondria, the powerhouse of the cell, which becomes damaged.
"We also have discovered a mechanism whereby 'normal' molecules of SOD1 are recruited in the presence of mutant SOD1 proteins to participate in the pathogenesis of ALS by forming intermolecular disulfide bonds," said Siddique. "This phenomenon is in some ways akin to the recruitment noted in prion disorders and provides molecular sites for therapeutic intervention." This molecular mechanism also may help explain other types of ALS in which no mutations have been detected in SOD1.
The normal form of SOD1 is a molecule composed of two identical parts, each with an amino acid chain, a copper ion, a zinc ion and an intramolecular disulfide linkage -- a bond within an SOD1 molecule that stabilizes the structure. Intermolecular disulfide bonds, or cross-links, are incorrect bonds that form between, not within, SOD1 molecules.
"A year ago we demonstrated that ALS mutations have the greatest effect on the most immature form of the SOD1 protein, causing it to misfold and form incorrect disulfide bonds that facilitate protein aggregation," said Thomas V. O'Halloran, professor of chemistry. "Those were test tube experiments, but we really wanted to know if we would find the same process in a physiological environment."
To investigate their hypothesis further, O'Halloran and Yoshiaki Furukawa, formerly a post-doctoral fellow in O'Halloran's lab, teamPage: 1 2 3 4 Related medicine news :1
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