ALS mutants of human superoxide dismutase form fibrous aggregates via framework destabilization.
Many point mutations in human Cu,Zn superoxide dismutase (SOD) cause familial amyotrophic lateral sclerosis (FALS), a fatal neurodegenerative disorder in heterozygotes. Here we show that these mutations cluster in protein regions influencing architectural integrity. Furthermore, crystal structures of SOD wild-type and FALS mutant H43R proteins uncover resulting local framework defects. Characterizations of beta-barrel (H43R) and dimer interface (A4V) FALS mutants reveal reduced stability and drastically increased aggregation propensity. Moreover, electron and atomic force microscopy indicate that these defects promote the formation of filamentous aggregates. The filaments resemble those seen in neurons of FALS patients and bind both Congo red and thioflavin T, suggesting the presence of amyloid-like, stacked beta-sheet interactions. These results support free-cysteine-independent aggregation of FALS mutant SOD as an integral part of FALS pathology. They furthermore provide a molecular basis for the single FALS disease phenotype resulting from mutations of diverse side-chains throughout the protein: many FALS mutations reduce structural integrity, lowering the energy barrier for fibrous aggregation.
DiDonato
Michael
M
Department of Molecular Biology, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, Maildrop MB4, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Craig
Lisa
L
Huff
Mary E
ME
Thayer
Maria M
MM
Cardoso
Rosa M F
RM
Kassmann
Carey J
CJ
Lo
Terence P
TP
Bruns
Cami K
CK
Powers
Evan T
ET
Kelly
Jeffery W
JW
Getzoff
Elizabeth D
ED
Tainer
John A
JA
D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000473:pathology; D001665:Binding Sites; D003300:Copper / Q000378:metabolism; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004795:Enzyme Stability; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D046911:Macromolecular Substances; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
D046911:Macromolecular Substances; D003300:Copper; D013482:Superoxide Dismutase; D015032:Zinc; D003545:Cysteine