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Protein Misfolding in Human Diseases
Linköping University, Department of Physics, Chemistry and Biology, Biochemistry. Linköping University, The Institute of Technology.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There are several diseases well known that are due to aberrant protein folding. These types of diseases can be divided into three main categories:

  1. Loss-of-function diseases
  2. Gain-of-toxic-function diseases
  3. Infectious misfolding diseases

 

Most loss-of-function diseases are caused by aberrant folding of important proteins. These proteins often misfold due to inherited mutations. The rare disease marble brain disease (MBD) also known as carbonic anhydrase II deficiency syndrome (CADS) can manifest in carriers of point mutations in the human carbonic anhydrase II (HCA II) gene. We have over the past 10-15 years studied the folding, misfolding and aggregation of the enzyme human carbonic anhydrase II. In summary our HCA II folding studies have shown that the protein folds via an intermediate of molten-globule type, which lacks enzyme activity and the molten globule state of HCA II is prone to aggregation. One mutation associated with MBD entails the His107Tyr (H107Y) substitution. We have demonstrated that the H107Y mutation is a remarkably destabilizing mutation influencing the folding behavior of HCA II. A mutational survey of position H107 and a neighboring conserved position E117 has been performed entailing the mutants H107A, H107F, H107N, E117A and the double mutants H107A/E117A and H107N/E117A. All mutants were severely destabilized versus GuHCl and heat denaturation. Thermal denaturation and GuHCl phase diagram and ANS analyses showed that the mutants shifted HCA II towards populating ensembles of intermediates of molten globule type under physiological conditions. The enormously destabilizing effects of the H107Y mutation is not due to loss of specific interactions of H107 with residue E117, instead it is caused by long range sterical destabilizing effects of the bulky tyrosine residue. We also showed that the folding equilibrium can be shifted towards the native state by binding of the small-molecule drug acetazolamide, and we present a small molecule inhibitor assessment with select sulfonamide inhibitors of varying potency to investigate the effectiveness of these molecules to inhibit the misfolding of HCA II H107Y. We also demonstrate that high concentration of the activator compound L-His increases the enzyme activity of the mutant but without stabilizing the folded protein.

 

The infectious misfolding diseases is the smallest group of misfolding diseases. The only protein known to have the ability to be infectious is the prion protein. The human prion diseases Kuru, Gerstmann-Sträussler-Scheinker disease (GSS) and variant Creutzfeldt-Jakob are characterized by depositions of amyloid plaque from misfolded prion protein (HuPrP) in various regions of the brain depending on disease. Amyloidogenesis of HuPrP is hence strongly correlated with prion disease.

Our results show that amyloid formation of recHuPrP90-231 can be achieved starting from the native protein under gentle conditions without addition of denaturant or altered pH. The process is efficiently catalyzed by addition of preformed recHuPrP90-231 amyloid seeds. It is plausible that amyloid seeding reflect the mechanism of transmissibility of prion diseases. Elucidating the mechanism of PrP amyloidogenesis is therefore of interest for strategic prevention of prion infection.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2009. , 103 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1239
Keyword [en]
Misfolding, carbonic anhydrase, prion protein, protein stability
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:liu:diva-21077ISBN: 978-91-7393-698-9 (print)OAI: oai:DiVA.org:liu-21077DiVA: diva2:240512
Public defence
2009-02-26, Planck, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2009-10-16 Created: 2009-09-28 Last updated: 2009-10-16Bibliographically approved
List of papers
1. Unfolding a folding disease: folding, misfolding and aggregation of the marble brain syndrome-associated mutant H107Y of human carbonic anhydrase II
Open this publication in new window or tab >>Unfolding a folding disease: folding, misfolding and aggregation of the marble brain syndrome-associated mutant H107Y of human carbonic anhydrase II
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2004 (English)In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 342, no 2, 619-633 p.Article in journal (Refereed) Published
Abstract [en]

Most loss-of-function diseases are caused by aberrant folding of important proteins. These proteins often misfold due to mutations. The disease marble brain syndrome (MBS), known also as carbonic anhydrase II deficiency syndrome (CADS), can manifest in carriers of point mutations in the human carbonic anhydrase II (HCA II) gene. One mutation associated with MBS entails the His107Tyr substitution. Here, we demonstrate that this mutation is a remarkably destabilizing folding mutation. The loss-of-function is clearly a folding defect, since the mutant shows 64% of CO2 hydration activity compared to that of the wild-type at low temperature where the mutant is folded. On the contrary, its stability towards thermal and guanidine hydrochloride (GuHCl) denaturation is highly compromised. Using activity assays, CD, fluorescence, NMR, cross-linking, aggregation measurements and molecular modeling, we have mapped the properties of this remarkable mutant. Loss of enzymatic activity had a midpoint temperature of denaturation (Tm) of 16 °C for the mutant compared to 55 °C for the wild-type protein. GuHCl-denaturation (at 4 °C) showed that the native state of the mutant was destabilized by 9.2 kcal/mol. The mutant unfolds through at least two equilibrium intermediates; one novel intermediate that we have termed the molten globule light state and, after further denaturation, the classical molten globule state is populated. Under physiological conditions (neutral pH; 37 °C), the His107Tyr mutant will populate the molten globule light state, likely due to novel interactions between Tyr107 and the surroundings of the critical residue Ser29 that destabilize the native conformation. This intermediate binds the hydrophobic dye 8-anilino-1-naphthalene sulfonic acid (ANS) but not as strong as the molten globule state, and near-UV CD reveals the presence of significant tertiary structure. Notably, this intermediate is not as prone to aggregation as the classical molten globule. As a proof of concept for an intervention strategy with small molecules, we showed that binding of the CA inhibitor acetazolamide increases the stability of the native state of the mutant by 2.9 kcal/mol in accordance with its strong affinity. Acetazolamide shifts the Tm to 34 °C that protects from misfolding and will enable a substantial fraction of the enzyme pool to survive physiological conditions.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2004
Keyword
Misfolding, loss-of-function, aggregation, molten globule, misfolding inhibitor
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-21072 (URN)10.1016/j.jmb.2004.07.024 (DOI)
Available from: 2009-09-28 Created: 2009-09-28 Last updated: 2017-12-13Bibliographically approved
2. Thermodynamic interrogation of a folding disease. Mutant mapping of position 107 in human carbonic anhydrase II linked to marble brain disease.
Open this publication in new window or tab >>Thermodynamic interrogation of a folding disease. Mutant mapping of position 107 in human carbonic anhydrase II linked to marble brain disease.
2008 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 47, no 5, 1288-1298 p.Article in journal (Refereed) Published
Abstract [en]

Marble brain disease (MBD) also known as Guibaud−Vainsel syndrome is caused by autosomal recessive mutations in the human carbonic anhydrase II (HCA II) gene. HCA II is a 259 amino acid single domain enzyme and is dominated by a 10-stranded β-sheet. One mutation associated with MBD entails the H107Y substitution where H107 is a highly conserved residue in the carbonic anhydrase protein family. We have previously demonstrated that the H107Y mutation is a remarkably destabilizing folding mutation [Almstedt et al. (2004) J. Mol. Biol. 342, 619−633]. Here, the exceptional destabilization by the H107Y mutation has been further investigated. A mutational survey of position H107 and a neighboring conserved position E117 has been performed entailing the mutants H107A, H107F, H107N, E117A and the double mutants H107A/E117A and H107N/E117A. All mutants were severely destabilized versus GuHCl and heat denaturation. Thermal denaturation and GuHCl phase diagram and ANS analyses showed that the mutants shifted HCA II toward populating ensembles of intermediates of molten globule type under physiological conditions. The native state stability of the mutants was in the following order:  wt > H107N > E117A > H107A > H107F > H107Y > H107N/E117A > H107A/E117A. In conclusion:  (i) H107N is least destabilizing likely due to compensatory H-bonding ability of the introduced Asn residue. (ii) Double mutant cycles surprisingly reveal additive destabilization of H107N and E117A showing that H107 and E117 are independently stabilizing the folded protein. (iii) H107Y and H107F are exceptionally destabilizing due to bulkiness of the side chains whereas H107A is more accommodating, indicating long-range destabilizing effects of the natural pathogenic H107Y mutation.

Place, publisher, year, edition, pages
Washington: ACS, 2008
Keyword
mutant mapping, carbonic anhydrase, misfolding, loss-of-function, molten globule
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-21056 (URN)10.1021/bi701720p (DOI)
Available from: 2009-09-28 Created: 2009-09-28 Last updated: 2017-12-13Bibliographically approved
3. Small-Molecule Suppression of Misfolding of Mutated Human Carbonic Anhydrase II Linked to Marble Brain Disease
Open this publication in new window or tab >>Small-Molecule Suppression of Misfolding of Mutated Human Carbonic Anhydrase II Linked to Marble Brain Disease
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2009 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 48, no 23, 5358-5364 p.Article in journal (Refereed) Published
Abstract [en]

Carbonic anhydrase II deficiency syndrome or Marble brain disease (MBD) is caused by autosomal recessive mutations in the human carbonic anhydrase II (HCA II) gene. Here we report a small-molecule stabilization study of the exceptionally destabilized HCA II mutant H107Y employing inhibitors based on p-aminobenzoyisulfonamide compounds and 1,3,4-thiadiazolylsulfonamides as well as amino acid activators. Protein stability assays showed a significant stabilization by the aromatic sulfonamide inhibitors when present at 10 mu M concentration, providing shifts of the midpoint of thermal denaturation between 10 degrees C and 16 degrees C and increasing the free energies of denaturation 0.5-3.0 kcal/mol as deduced from GuHCl denaturation. This study could be used as a starting point for the design of small-molecule folding modulators and possibly autoactivatable molecules for suppression of misfolding of destabilized HCA II mutants.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19548 (URN)10.1021/bi900128e (DOI)
Note
On the day of the defence date tha status of this articel was In Manuscript.Available from: 2009-06-29 Created: 2009-06-26 Last updated: 2017-12-13Bibliographically approved
4. Amyloid fibrils of human prion protein are spun and woven from morphologically disordered aggregates
Open this publication in new window or tab >>Amyloid fibrils of human prion protein are spun and woven from morphologically disordered aggregates
2009 (English)In: Prion, ISSN 1933-6896, Vol. 3, no 4, 224-235 p.Article in journal (Refereed) Published
Abstract [en]

Propagation and infectivity of prions in human prionopathies are likely associated with conversion of the mainly α-helical human prion protein, HuPrP, into an aggregated form with amyloid-like properties. Previous reports on efficient conversion of recombinant HuPrP have used mild to harsh denaturing conditions to generate amyloid fibrils in vitro. Herein we report on the in vitro conversion of four forms of truncated HuPrP (sequences 90-231 and 121-231 with and without an N-terminal hexa histidine tag) into amyloid-like fibrils within a few hours by using a protocol (phosphate buffered saline solutions at neutral pH with intense agitation) close to physiological conditions. The conversion process monitored by thioflavin T, ThT, revealed a three stage process with lag, growth and equilibrium phases. Seeding with preformed fibrils shortened the lag phase demonstrating the classic nucleated polymerization mechanism for the reaction. Interestingly, comparing thioflavin T kinetics with solubility and turbidity kinetics it was found that the protein initially formed non-thioflavionophilic, morphologically disordered aggregates that over time matured into amyloid fibrils. By transmission electron microscopy and by fluorescence microscopy of aggregates stained with luminescent conjugated polythiophenes (LCPs); we demonstrated that HuPrP undergoes a conformational conversion where spun and woven fibrils protruded from morphologically disordered aggregates. The initial aggregation functioned as a kinetic trap that decelerated nucleation into a fibrillation competent nucleus, but at the same time without aggregation there was no onset of amyloid fibril formation. The agitation, which was necessary for fibril formation to be induced, transiently exposes the protein to the air-water interface suggests a hitherto largely unexplored denaturing environment for prion conversion.

Place, publisher, year, edition, pages
Austin: Landes Bioscience Journals, 2009
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-21064 (URN)10.4161/pri.3.4.10112 (DOI)000280061100009 ()
Available from: 2009-09-28 Created: 2009-09-28 Last updated: 2014-09-09

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