Didonato M, Craig L, Huff ME, Thayer MM, Cardoso RM, Kassmann CJ, Lo TP, Bruns CK, Powers ET, Kelly JW, Getzoff ED, Tainer JA. ALS mutants of human superoxide dismutase form fibrous aggregates via framework destabilization. J Mol Biol. 2003 Sep 19;332(3):601-15. PubMed.
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University of North Carolina
DiDonato and coworkers have studied the cysteine-independent aggregation of two FALS-associated SOD mutants, H43R and A4V. They found that both mutants have reduced stability (as found by guanidine-HCl denaturation) and activity with respect to the wild-type. Further, the pH-induced propensity of destabilized mutants to aggregate was probed by light scattering and the final fibrous aggregates were visualized by electron microscopy. It was found that the metal-free Apo-state of the enzyme was more prone to aggregation. These aggregates bound to Congo red and thioflavin T, indicating that the aggregates might have characteristic amyloid fibrils. However, a previous study (Stathopulos et al., 2003) of heat and TFE-induced aggregation shows that the binding is much weaker and the topology of in-vivo fibrils may be less ordered. Thus, aggregate morphologies may vary due to differences in the in-vitro conditions at which they are generated. The authors also found that the diameters of H43R fibrils were smaller than one native protein subunit, indicating that SOD possibly undergoes compaction before assembling into fibrils. The above observation is very interesting, given that proteins normally unfold/misfold (into expanded states) before aggregation, hinting at possible early events in SOD aggregation.
References:
Stathopulos PB, Rumfeldt JA, Scholz GA, Irani RA, Frey HE, Hallewell RA, Lepock JR, Meiering EM. Cu/Zn superoxide dismutase mutants associated with amyotrophic lateral sclerosis show enhanced formation of aggregates in vitro. Proc Natl Acad Sci U S A. 2003 Jun 10;100(12):7021-6. PubMed.
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