The structural plasticity of the human copper chaperone for SOD1 - insights from combined size exclusion chromatographic and solution X-ray scattering studies
Résumé
The incorporation of copper into biological macromolecules such as Cu-Zn superoxide dismutase (SOD1) is essential for the viability of most organisms. However, copper is toxic and therefore the intracellular free copper concentration is kept to an absolute minimum. Several proteins, termed metallochaperones, are charged with the responsibility of delivering copper from membrane transporters to its intracellular destination. The Copper Chaperone for SOD1 (CCS) is the major pathway for SOD1 copper loading. We have determined the first solution structure of hCCS by Small Angle X-ray Scattering (SAXS) in conjunction with size exclusion chromatography (SEC). Our findings highlight the importance of this combined on-line chromatographic technology with SAXS, which has allowed us to unambiguously separate the hCCS dimer from other oligomeric and non-physiological aggregated states that would otherwise adversely effect measurements performed on bulk solutions. Our work exposes the dynamic molecular conformation of this multi-domain chaperone in solution. The metal binding domains known to be responsible for the conveyance of copper to SOD1 can be found in positions that would expedite this movement. Domains I and III of a single hCCS monomer are able to interact and can also move into positions that would facilitate initial copper binding and ultimately transfer to SOD1. Conversely, the interpretation of our solution studies is not compatible with an interaction between these domains and their counterparts in a hCCS dimer. Overall, our results reveal the plasticity of this multi-domain chaperone in solution and are consistent with an indispensable flexibility necessary for executing its dual functions of metal binding and transfer.
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