The coupling between disulphide status, metallation and dimer interface strength in Cu/Zn superoxide dismutase.
The gain of neurotoxic function in amyotrophic lateral sclerosis (ALS) has been linked to misfolding of the homodimeric enzyme Cu/Zn superoxide dismutase (SOD). Here, we present the crystal structure of fully cysteine-depleted human SOD (SOD(CallA)), representing a reduced, marginally stable intermediate on the folding pathway in vivo that has also been implicated as neurotoxic precursor state. A hallmark of this species is that it fails to dimerize and becomes trapped as a monomer in the absence of the active-site metals. The crystallographic data show that removal of the C57-C146 disulphide bond sets free the interface loop IV in the apo protein, whereas the same loop remains unaffected in the holo protein. Thus, the low dimerisation propensity of disulphide-reduced apoSOD seems to be of entropic origin due to increased loop flexibility in the monomeric state: in the disulphide-reduced holo protein this gain in configurational entropy upon splitting of the dimer interface is reduced by the metal coordination.
Hörnberg
Andreas
A
Department of Biochemistry, Umeå University, SE-901 87 Umeå, Sweden.
Logan
Derek T
DT
Marklund
Stefan L
SL
Oliveberg
Mikael
M
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003603:Cytotoxins / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D004795:Enzyme Stability; D006801:Humans; D008961:Models, Structural; D009154:Mutation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*
D003603:Cytotoxins; D004220:Disulfides; D003300:Copper; D013482:Superoxide Dismutase; D015032:Zinc