Protein instability and altered folding associated with ALS
1
Newsdesk 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 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 462 http://neurology.thelancet.com Vol 4 August 2005 Protein instability and altered folding associated with ALS 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 dys- kinesia 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 wild- type 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 [parox- ysmal dyskinesia] indeed represent a distinct syndrome (GEPD)”, states corr- esponding author Qing Wang. They also suggest that Asp434Gly is a gain- of-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 channel- opathies to be identified. Nevertheless”, he adds, “some of these might only affect very small numbers of families”. Vivien Chen Channelopathy linked to epilepsy and paroxysmal dyskinesia
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Transcript of Protein instability and altered folding associated with ALS
Newsdesk
There are 114 mutations in the geneencoding Cu/Zn superoxide dismutase(SOD) associated with amyotrophiclateral sclerosis (ALS). Misfolding andaggregation of mutant SOD1 werethought to be an essential part ofdisease progression in ALS. Now,researchers report a link betweenaltered folding patterns, proteinstability, net charge, and survival timein patients carrying the mutations.
“We selected the 15 mutations thathad the most reliable and sufficientclinical data available, and trackedthem in vitro, with respect to howthey folded”, explains study authorMikael Oliveberg (Umeå University,Umeå, Sweden). “All of the mutationsperturbed the folding pattern of theprotein. It is what we expected, but noone had ever shown it before.”
The cytotoxic component of severalneurodegenerative disorders, includingALS, Parkinson’s disease, and
Lund–Huntington’s disease, seems tobe ordered oligomeric states oraggregates of unfolded or misfoldedproteins. Oliveberg and colleaguesmapped out and compared the foldingbehaviour of ALS-associated mutantsand survival times to ascertain theorigin of neurotoxicity in ALS (Proc NatlAcad Sci 2005, published onlineJune 27, DOI: 50195710).
Oliveberg’s group assessed thekinetics of SOD1 monomer folding andunfolding, and of dimer association anddissociation, and showed that themutations increase the cellularconcentration of immature monomers.They also identified an associationbetween protein instability and diseaseprogression: the more unstable theprotein, the quicker the diseaseprogression. The protein is alsonegatively charged and reduction ofthe negative charge seems to decreasesurvival time.
For future clinical applications ofthese findings, Oliveberg points outthat protein stability is a major factor.“If you can design a drug that canstabilise the protein, you may be able toat least slow down the progression ofthe disease.”
This work supports the results of astudy by Ray and colleagues (Proc NatlAcad Sci USA 2005; 102: 3639–44)who identified molecules that stabilisethe SOD1 dimer interface, commentsLinda Greensmith (University CollegeLondon, UK). “Together the work ofthese two groups suggests a promisingmethod for the rational design ofpotential therapeutic compounds,which may shift the equilibrium ofmutant SOD1 protein folding in favourof the stable dimerised protein as ameans of delaying disease progressionin ALS”, she says.
Roxanne Nelson
462 http://neurology.thelancet.com Vol 4 August 2005
Protein instability and altered folding associated with ALS
Scientists have shown that coexistentgeneralised epilepsy and paroxysmaldyskinesia (GEPD) are linked tomutations in an ion channel gene,which suggests this disorder may be achannelopathy. Although not ascommon as epilepsy, paroxysmal dys-kinesia is also characterised by suddenattacks of involuntary movement.
Wei Du and colleagues (ClevelandClinic Foundation, Cleveland, OH, USA)genetically analysed a large family withGEPD and found that a mutation in aregion of chromosome 10q22 waslinked with the disorder (Nat Genet2005; published online June 5,DOI:10.1038/ng1585). The researcherssuggest that such mutations could bethe underlying cause of GEPD.
Du and colleagues went on to identifya 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 ofaspartic acid with glycine (Asp434Gly)and disrupts normal calcium ion affinityand BK channel activation.
Additionally, more current wasinduced at the same membranepotential in mutant BK channels thanin wild-type channels. The researcherspostulated that during an actionpotential, more mutant than wild-type channels open in response todepolarisation and calcium ion entry,which causes a fast repolarisation.Notably, mutant channels were moresensitive to calcium than wild-typechannels, by contrast with otherknown mutations of the � subunit,which reduce calcium sensitivity.
Du’s team concludes that raisedcalcium sensitivity could result in anincrease in potassium conductance ofthe BK channel, brain excitability, and,ultimately, GEPD. "Our study providesstrong genetic evidence confirming
that coexistent epilepsy and [parox-ysmal dyskinesia] indeed represent adistinct syndrome (GEPD)”, states corr-esponding author Qing Wang. Theyalso suggest that Asp434Gly is a gain-of-function mutation, with a possiblesynergistic effect with ethanol to triggerGEPD. Thus BK channels could betargeted for treatment.
This study “confirms that the list ofchannels implicated in monogenicneurological disease is not exhausted”,comments Dimitri Kullmann (Instituteof Neurology, University CollegeLondon, UK). “Given that there areseveral hundred ion-channel genesexpressed in the brain, and only a dozenor so known CNS channelopathies,there are probably many more channel-opathies to be identified. Nevertheless”,he adds, “some of these might onlyaffect very small numbers of families”.
Vivien Chen
Channelopathy linked to epilepsy and paroxysmal dyskinesia
