Download - Diseases caused by mutations in chaperones - α-crystallin, MKKS/BBS6 chaperonin Neurodegenerative diseases - prions, Huntington’s disease Protein misfolding.

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Diseases caused by mutations in chaperones- α-crystallin, MKKS/BBS6 chaperonin

Neurodegenerative diseases- prions, Huntington’s disease

Protein misfolding diseasesProtein misfolding diseases12-1

pathogenesis of many neurodegenerative disorders is due to abnormal protein conformation

common theme in diseases is conversion of normal cellular and/or circulating protein into an insoluble, aggregated, beta-sheet rich form which is deposited in the brain as an amyloid

deposits are toxic and produce neuronal dysfunction and death

prion-related diseases occur when conversion of a normal prion protein, PrP, into an infectious and pathogenic form, PrPSc (Prion Protein Scrapie). Prion diseases:

Creutzfeld Jacob disease, Kuru, Gerstmann-Straussler-Scheinker disease, Fatal familial insomnia, Scrapie (sheep), Bovine spongiform encephalopathy (BSE or ‘mad cow’), chronic wasting disease (mule deer, elk), feline spongiform encephalopathy

the conversion of PrP into PrPSc is a conformational one; the PrPSc form is more resistant to proteases and is detergent-insoluble

PrPSc forms amyloid fibrils in the brain; injection of this material into the brains of normal mice leads to disease

the normal function of PrP is unknown; transgenic mice lacking this protein grow normally

Other proteins unrelated in sequence to PrP have similar properties:

e.g., yeast Sup35, Ure2p

Neurodegenerative disorders:Neurodegenerative disorders: prions prions12-2

Note:

- testing for infectivity with PrPSc is done by injecting brain material from an infected animal into the brain of another animal

- transgenic mice devoid of mouse PrP cannot be infected by mouse PrPSc

contains hamster PrP(lacks mouse PrP)

contains hamster PrP(lacks mouse PrP)

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Prion transmission characteristicsPrion transmission characteristics

harbours hamster PrPSc harbours murine PrPSc

Feldman et al. (1999) Formation of the VHL-Elongin BC tumor suppressor complex is mediated by the chaperonin TRiC. Mol. Cell 4, 1051-1061.

TRiC stands for TCP-1 Ring Complex and is the same eukaryotic cytosolic chaperonin as CCT (Chaperonin containing TCP-1). CCT was first thought to assist the folding of only actins and tubulins, but recently, it has been found to bind ~10% of all cell proteins and is known to assist the folding of numerous other proteins, including a viral capsid protein, myosin, luciferase and VHL.

Class PresentationsClass Presentations12-4

Johnston et al. (1998) Aggresomes: a cellular response to misfolded proteins. J. Cell Biol. 143, 1883-98.

there exists a cellular mechanism by which misfolded/aggregated proteins are sequestered in the cell such sequestration occurs near the centrosome in an organelle-like structure commonly termed ‘aggresome’

Huntington’s disease (HD) is a very common syndrome that affects numerous people

It is caused by the expansion of CAG trinucleotide repeats (encoding polyglutamine) within a large protein (350 kDa) termed huntingtin

the function of huntingtin is unclear; evidence points to trafficking (vesicular)

normal and disease forms

unaffected individuals carry between 6 and 39 repeats in exon 1 of huntingtin

HD patients typically have between 36-180 repeats in exon 1 of huntingtin

mutant forms of huntingtin with expanded repeats form nuclear and cytoplasmic aggregates in human brain tissue

Neurodegenerative disorders:Neurodegenerative disorders: Huntington’s diseaseHuntington’s disease

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can express protein fusion with different numbers of CAG repeats and study

Muchowski et al. (2000) PNAS 97, 7841. produced GST-HD proteins (HD20Q and HD53Q) then cleaved off HD from tag using protease that cleaves between GST and HD; aggregation was then followed in the presence or absence of chaperones

found that combination of Hsp40 and DnaK were most effective at preventing aggregation

after 8 hours;aggregation assayed

as in (A)

time course ofaggregation

time course ofaggregation detected by

‘filter trap’ assay

Huntington’s disease: Huntington’s disease: in vitro in vitro model systemmodel system

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GST-HD proteins were induced to aggregate by cleavage (as before) in the presence or absence of chaperones

fibrils/aggregate formation was observed by electron microscopy

Suppression of HD exon 1 fibril formation by Hsp40 and Hsp70 in vitro. GST-HD fusion protein (3 µM) was incubated with PreScission protease for 5 h as in previous slide:

in the absence (A) or presence (B-F) of chaperones (6 µM)

(B) DnaK

(C) DnaJ

(D) Hdj-1

(E) Hsc70/ATP

(F) Hsc70/Hdj-1/ATP (Hsc70/Hdj-1 = 2:1). Samples then were analyzed by EM. (Bar = 100 nm.)

Huntington’s disease: Huntington’s disease: in vitro in vitro model systemmodel system

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control

DnaK

DnaJ

Hdj-1

Hsp70/ATP

Hsc70/Hdj-1

Huntingtin constructs with Exon 1 and containing 20, 39 or 53 CAG repeats as well as a c-myc tag (which is recognized by antibody and can be immunoprecipitated) were expressed in S. cerevisiae

(A) *=SDS-insoluble aggregates that do not penetrate the gel

(A) **=degradation product of full-length protein

(B) filter-trap assay; T=total, S=soluble, P=pellet after centrifugation

(D) immunoprecipitation of different proteins with anti Ssa (cytosolic) and Ssb (ribosome-bound) Hsp70 protein homologues from yeast, as well as anti-Ydj1 (Hsp40 homologue)

High-level expression of Hsp70/40 in yeast with HD53Q made the aggregates SDS-soluble! (not shown)

Huntington’s disease: Huntington’s disease: in vivo in vivo yeastyeast model systemmodel system

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expressed HA-tagged 127 CAG repeat-protein (127Q) in the eye, causing abnormalities/polyQ deposits

GMR has 5 tandem copies of a response element derived from the rhodopsin 1 gene promoter)

GAL4 is a transcription factor

UAS, ‘Upstream Activating Sequence’ required for GAL4-dependent gene expression

flies carrying GMR-GAL + UAS127Q were crossed with EP-element insertion strains (7000)

screened for suppression or enhancement of toxicity

found: dhdJ1, an Hsp40 homologue; dtpr2 is a TPR-containing protein with J domain

Esfarjani and Benzer (2000) Science 287, 1837.

Huntington’s disease: Huntington’s disease: DrosophilaDrosophila model system model system

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still see aggregates (as with the in vitro studies)

GAL4GAL4

127Q127Q

GMR GMR GMRGMRGMR

UAS

TRANSGENIC STRAIN CARRYINGGMR PROMOTER-GAL4 CONSTRUCT(HIGH-LEVEL EXPRESSION IN EYE)

CONTRUCT CROSSED INTO THE ABOVE STRAIN(UAS ACTIVATED BY GAL4 TO INDUCE HIGH-LEVEL EXPRESSION OF 127Q)

α-crystallin belongs to the class of molecular chaperones collectively termed small heat-shock proteins functions include (but is not limited to) maintaining microfilament stability (e.g., intermediate filaments and perhaps actin and tubulin) present in all tissue types and ubiquitous in the three domains

mutations in α-crystallin genes A and B cause some major ailments:

αα-crystallin and disease-crystallin and disease 12-10

cataracts- function is as a structural protein as well as a molecular chaperone; it makes up nearly 1/3 of the eye lens protein, while β- and γ-crystallins make up close to the other 2/3

desmin-related myopathy- desmin is an intermediate filament; mutation in the chaperone result in the accumulation of intracellular aggregates of desmin (co-aggregation with α-crystallin occurs)

Alexander’s disease- the neurodegenerative Alexander's disease is characterized by GFAP co-aggregates with α-crystallin; GFAP is closely related to desmin

R120G α-crystallin mutant is found in some patients

the chaperone activity of the R120G mutant (located in the highly conserved α-crystallin domain) is not completely lost compared to the wild-type chaperone intact (as judged by prevention-of-aggregation experiments)

reason why the mutant chaperone associates more strongly with GFAP (and desmin) is unclear

specificity of binding causing the problem?

GFAP+

wt α -crystallin

GFAP+

R120G α -crystallin

Association of α-crystallin (wild-type and mutant) with GFAP at 37ºC

Perng et al. (1999) J. Biol. Chem. 274, 33235.

αα-crystallin-GFAP experiment-crystallin-GFAP experiment12-11

MKKS/BBS6 is one of 12 genes that cause Bardet-Biedl Syndrome (i.e., a polygenic disorder)

mapping of BBS genes relied on screening inbred populations (e.g., Bedoin arabs, Old Order Amish, Newfoundland)

BBS phenotypes: obesity, kidney and liver problems, retinal degeneration, cardiomyopathy, diabetes, mental retardation, anosmia, hearing impairment, polydactyly, etc.

MKKS/BBS6 is related to the chaperonin CCT

two other chaperonin-like genes were found: BBS10, BBS12

MKKS/BBS6 mutations cause diseaseMKKS/BBS6 mutations cause disease12-12

the chaperonin is related to the eukaryotic cytosolic chaperonin CCT it is found only in vertebrates and ‘more evolved’ organisms it is highly divergent although it is clearly a Group II chaperonin

PE EA AE, equatorial domainA, apical domainI, intermediate domainP, protrusion

I I

BBS4 is involved in microtubule anchoring; it contains multiple TPR motifs: 34 amino acid repeats of helix-loop-helix

- TPRs are protein-protein interaction domains

BBS proteins are required for proper cilia function; BBS is therefore a ciliopathy improper function of ciliary genes results in numerous ailments, including retinal degeneration, polycystic kidneys, skeletal anomalies, etc.

MKKS/BBS6 and other BBS allelesMKKS/BBS6 and other BBS alleles12-13