Copper binding regulates intracellular alpha-synuclein localisation, aggregation and toxicity.

Alpha-synuclein is a natively unfolded protein that aggregates and forms inclusions that are associated with a range of diseases that include Parkinson's Disease and Dementia with Lewy Bodies. The mechanism behind the formation of these inclusions and their possible role in disease remains unclear. Alpha-synuclein has also been shown to bind metals including copper and iron. We used a cell culture model of alpha-synuclein aggregation to examine the relationship between metals and formation of aggregates of the protein. While the levels of iron appear to have no role in aggregate formation or localisation of the protein in cells, copper appears to be important for both aggregation and cellular localisation of alpha-synuclein. Reduction in cellular copper resulted in a great decrease in aggregate formation both in terms of large aggregates visible in cells and oligomers observed in western blot analysis of cell extracts. Reduction in copper also resulted in a change in localisation of the protein which became more intensely localised to the plasma membrane in medium with low copper. These changes were reversed when copper was restored to the cells. Mutants of the copper binding domains altered the response to copper. Deletion of either the N- or C-termini resulted in a loss of aggregation while deletion of the C-termini also resulted in a loss of membrane association. Increased expression of alpha-synuclein also increased cell sensitivity to the toxicity of copper. These results suggest that the potential pathological role of alpha-synuclein aggregates is dependent upon the copper binding capacity of the protein.

Amyloidogenic metal-binding proteins: new investigative pathways.

Neurodegenerative diseases remain perplexing and problematic for modern research. Those associated with amyloidogenic proteins have often been lumped together simply because those proteins aggregate. However, research has identified a more logical reason to group some of these diseases together. The associated proteins not only aggregate, but also bind copper. The APP (amyloid precursor protein) binds copper in an N-terminal region. Binding of copper has been suggested to influence generation of beta-amyloid from the protein. PrP (prion protein) binds copper, and this appears to be necessary for its normal function and might also reduce its probability of conversion into an infectious prion. alpha-Synuclein, a protein associated with Parkinson's disease, also binds copper, but, in this case, it potentially increases the rate at which the protein aggregates. The similarities between these proteins, in terms of metal binding, has allowed us to investigate them using similar approaches. In the present review, we discuss some of these approaches.

Alpha-synuclein is a cellular ferrireductase.

α-synuclein (αS) is a cellular protein mostly known for the association of its aggregated forms with a variety of diseases that include Parkinson's disease and Dementia with Lewy Bodies. While the role of αS in disease is well documented there is currently no agreement on the physiological function of the normal isoform of the protein. Here we provide strong evidence that αS is a cellular ferrireductase, responsible for reducing iron (III) to bio available iron (II). The recombinant form of the protein has a V(Max) of 2.72 nmols/min/mg and K(m) 23 µM. This activity is also evident in lysates from neuronal cell lines overexpressing αS. This activity is dependent on copper bound to αS as a cofactor and NADH as an electron donor. Overexpression of α-synuclein by cells significantly increases the percentage of iron (II) in cells. The common disease mutations associated with increased susceptibility to PD show no [corrected] differences in activity or iron (II) levels. This discovery may well provide new therapeutic targets for PD and Lewy body dementias.