Disease-associated mutations at copper ligand histidine residues of superoxide dismutase 1 diminish the binding of copper and compromise dimer stability.
A subset of superoxide dismutase 1 (Cu/Zn-SOD1) mutants that cause familial amyotrophic lateral sclerosis (FALS) have heightened reactivity with (-)ONOO and H(2)O(2) in vitro. This reactivity requires a copper ion bound in the active site and is a suggested mechanism of motor neuron injury. However, we have found that transgenic mice that express SOD1-H46R/H48Q, which combines natural FALS mutations at ligands for copper and which is inactive, develop motor neuron disease. Using a direct radioactive copper incorporation assay in transfected cells and the established tools of single crystal x-ray diffraction, we now demonstrate that this variant does not stably bind copper. We find that single mutations at copper ligands, including H46R, H48Q, and a quadruple mutant H46R/H48Q/H63G/H120G, also diminish the binding of radioactive copper. Further, using native polyacrylamide gel electrophoresis and a yeast two-hybrid assay, the binding of copper was found to be related to the formation of the stable dimeric enzyme. Collectively, our data demonstrate a relationship between copper and assembly of SOD1 into stable dimers and also define disease-causing SOD1 mutants that are unlikely to robustly produce toxic radicals via copper-mediated chemistry.
Wang
Jiou
J
Department of Pathology, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Caruano-Yzermans
Amy
A
Rodriguez
Angela
A
Scheurmann
Jonathan P
JP
Slunt
Hilda H
HH
Cao
Xiaohang
X
Gitlin
Jonathan
J
Hart
P John
PJ
Borchelt
David R
DR
D000818:Animals; D003300:Copper / Q000737:chemistry*; D019281:Dimerization; D006639:Histidine / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D051379:Mice; D008822:Mice, Transgenic; D008958:Models, Molecular; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D011485:Protein Binding; D013482:Superoxide Dismutase / Q000737:chemistry*; D020798:Two-Hybrid System Techniques
D008024:Ligands; D006639:Histidine; D003300:Copper; D013482:Superoxide Dismutase