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Protein instability and altered folding associated with ALS
Newsdesk
Channelopathy linked to epilepsy and paroxysmal dyskinesia Scientists have shown that coexistent generalised epilepsy and paroxysmal dyskinesia (GEPD) are linked to mutations in an ion channel gene, which suggests this disorder may be a channelopathy. Although not as common as epilepsy, paroxysmal dyskinesia is also characterised by sudden attacks of involuntary movement. Wei Du and colleagues (Cleveland Clinic Foundation, Cleveland, OH, USA) genetically analysed a large family with GEPD and found that a mutation in a region of chromosome 10q22 was linked with the disorder (Nat Genet 2005; published online June 5, DOI:10.1038/ng1585). The researchers suggest that such mutations could be the underlying cause of GEPD. Du and colleagues went on to identify a mutation in one such gene, KCNMA1, which encodes the pore-forming subunit of the big potassium ion (BK) channel, in the study family. The
mutation results in the substitution of aspartic acid with glycine (Asp434Gly) and disrupts normal calcium ion affinity and BK channel activation. Additionally, more current was induced at the same membrane potential in mutant BK channels than in wild-type channels. The researchers postulated that during an action potential, more mutant than wildtype channels open in response to depolarisation and calcium ion entry, which causes a fast repolarisation. Notably, mutant channels were more sensitive to calcium than wild-type channels, by contrast with other known mutations of the subunit, which reduce calcium sensitivity. Du’s team concludes that raised calcium sensitivity could result in an increase in potassium conductance of the BK channel, brain excitability, and, ultimately, GEPD. "Our study provides strong genetic evidence confirming
that coexistent epilepsy and [paroxysmal dyskinesia] indeed represent a distinct syndrome (GEPD)”, states corresponding author Qing Wang. They also suggest that Asp434Gly is a gainof-function mutation, with a possible synergistic effect with ethanol to trigger GEPD. Thus BK channels could be targeted for treatment. This study “confirms that the list of channels implicated in monogenic neurological disease is not exhausted”, comments Dimitri Kullmann (Institute of Neurology, University College London, UK). “Given that there are several hundred ion-channel genes expressed in the brain, and only a dozen or so known CNS channelopathies, there are probably many more channelopathies to be identified. Nevertheless”, he adds, “some of these might only affect very small numbers of families”.
Vivien Chen
Protein instability and altered folding associated with ALS There are 114 mutations in the gene encoding Cu/Zn superoxide dismutase (SOD) associated with amyotrophic lateral sclerosis (ALS). Misfolding and aggregation of mutant SOD1 were thought to be an essential part of disease progression in ALS. Now, researchers report a link between altered folding patterns, protein stability, net charge, and survival time in patients carrying the mutations. “We selected the 15 mutations that had the most reliable and sufficient clinical data available, and tracked them in vitro, with respect to how they folded”, explains study author Mikael Oliveberg (Umeå University, Umeå, Sweden). “All of the mutations perturbed the folding pattern of the protein. It is what we expected, but no one had ever shown it before.” The cytotoxic component of several neurodegenerative disorders, including ALS, Parkinson’s disease, and 462
Lund–Huntington’s disease, seems to be ordered oligomeric states or aggregates of unfolded or misfolded proteins. Oliveberg and colleagues mapped out and compared the folding behaviour of ALS-associated mutants and survival times to ascertain the origin of neurotoxicity in ALS (Proc Natl Acad Sci 2005, published online June 27, DOI: 50195710). Oliveberg’s group assessed the kinetics of SOD1 monomer folding and unfolding, and of dimer association and dissociation, and showed that the mutations increase the cellular concentration of immature monomers. They also identified an association between protein instability and disease progression: the more unstable the protein, the quicker the disease progression. The protein is also negatively charged and reduction of the negative charge seems to decrease survival time.
For future clinical applications of these findings, Oliveberg points out that protein stability is a major factor. “If you can design a drug that can stabilise the protein, you may be able to at least slow down the progression of the disease.” This work supports the results of a study by Ray and colleagues (Proc Natl Acad Sci USA 2005; 102: 3639–44) who identified molecules that stabilise the SOD1 dimer interface, comments Linda Greensmith (University College London, UK). “Together the work of these two groups suggests a promising method for the rational design of potential therapeutic compounds, which may shift the equilibrium of mutant SOD1 protein folding in favour of the stable dimerised protein as a means of delaying disease progression in ALS”, she says.
Roxanne Nelson http://neurology.thelancet.com Vol 4 August 2005
Channelopathy linked to epilepsy and paroxysmal dyskinesia Scientists have shown that coexistent generalised epilepsy and paroxysmal dyskinesia (GEPD) are linked to mutations in an ion channel gene, which suggests this disorder may be a channelopathy. Although not as common as epilepsy, paroxysmal dyskinesia is also characterised by sudden attacks of involuntary movement. Wei Du and colleagues (Cleveland Clinic Foundation, Cleveland, OH, USA) genetically analysed a large family with GEPD and found that a mutation in a region of chromosome 10q22 was linked with the disorder (Nat Genet 2005; published online June 5, DOI:10.1038/ng1585). The researchers suggest that such mutations could be the underlying cause of GEPD. Du and colleagues went on to identify a mutation in one such gene, KCNMA1, which encodes the pore-forming subunit of the big potassium ion (BK) channel, in the study family. The
mutation results in the substitution of aspartic acid with glycine (Asp434Gly) and disrupts normal calcium ion affinity and BK channel activation. Additionally, more current was induced at the same membrane potential in mutant BK channels than in wild-type channels. The researchers postulated that during an action potential, more mutant than wildtype channels open in response to depolarisation and calcium ion entry, which causes a fast repolarisation. Notably, mutant channels were more sensitive to calcium than wild-type channels, by contrast with other known mutations of the subunit, which reduce calcium sensitivity. Du’s team concludes that raised calcium sensitivity could result in an increase in potassium conductance of the BK channel, brain excitability, and, ultimately, GEPD. "Our study provides strong genetic evidence confirming
that coexistent epilepsy and [paroxysmal dyskinesia] indeed represent a distinct syndrome (GEPD)”, states corresponding author Qing Wang. They also suggest that Asp434Gly is a gainof-function mutation, with a possible synergistic effect with ethanol to trigger GEPD. Thus BK channels could be targeted for treatment. This study “confirms that the list of channels implicated in monogenic neurological disease is not exhausted”, comments Dimitri Kullmann (Institute of Neurology, University College London, UK). “Given that there are several hundred ion-channel genes expressed in the brain, and only a dozen or so known CNS channelopathies, there are probably many more channelopathies to be identified. Nevertheless”, he adds, “some of these might only affect very small numbers of families”.
Vivien Chen
Protein instability and altered folding associated with ALS There are 114 mutations in the gene encoding Cu/Zn superoxide dismutase (SOD) associated with amyotrophic lateral sclerosis (ALS). Misfolding and aggregation of mutant SOD1 were thought to be an essential part of disease progression in ALS. Now, researchers report a link between altered folding patterns, protein stability, net charge, and survival time in patients carrying the mutations. “We selected the 15 mutations that had the most reliable and sufficient clinical data available, and tracked them in vitro, with respect to how they folded”, explains study author Mikael Oliveberg (Umeå University, Umeå, Sweden). “All of the mutations perturbed the folding pattern of the protein. It is what we expected, but no one had ever shown it before.” The cytotoxic component of several neurodegenerative disorders, including ALS, Parkinson’s disease, and 462
Lund–Huntington’s disease, seems to be ordered oligomeric states or aggregates of unfolded or misfolded proteins. Oliveberg and colleagues mapped out and compared the folding behaviour of ALS-associated mutants and survival times to ascertain the origin of neurotoxicity in ALS (Proc Natl Acad Sci 2005, published online June 27, DOI: 50195710). Oliveberg’s group assessed the kinetics of SOD1 monomer folding and unfolding, and of dimer association and dissociation, and showed that the mutations increase the cellular concentration of immature monomers. They also identified an association between protein instability and disease progression: the more unstable the protein, the quicker the disease progression. The protein is also negatively charged and reduction of the negative charge seems to decrease survival time.
For future clinical applications of these findings, Oliveberg points out that protein stability is a major factor. “If you can design a drug that can stabilise the protein, you may be able to at least slow down the progression of the disease.” This work supports the results of a study by Ray and colleagues (Proc Natl Acad Sci USA 2005; 102: 3639–44) who identified molecules that stabilise the SOD1 dimer interface, comments Linda Greensmith (University College London, UK). “Together the work of these two groups suggests a promising method for the rational design of potential therapeutic compounds, which may shift the equilibrium of mutant SOD1 protein folding in favour of the stable dimerised protein as a means of delaying disease progression in ALS”, she says.
Roxanne Nelson http://neurology.thelancet.com Vol 4 August 2005