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Aggregation-Induced Folding of a de novo Designed Polypeptide Immobilized on Gold Nanoparticles
Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.ORCID iD: 0000-0002-7001-9415
Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
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2006 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 7, 2194 -2195 p.Article in journal (Refereed) Published
Abstract [en]

This communication reports the first steps in the construction of a novel, nanoparticle-based hybrid material for biomimetic and biosensor applications. Gold nanoparticles were modified with synthetic polypeptides to enable control of the particle aggregation state in a switchable manner, and particle aggregation was, in turn, found to induce folding of the immobilized peptides.

Place, publisher, year, edition, pages
ACS Publications , 2006. Vol. 128, no 7, 2194 -2195 p.
Keyword
Not aviable
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:liu:diva-14041DOI: 10.1021/ja057056jOAI: oai:DiVA.org:liu-14041DiVA: diva2:22504
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Protein-protein interactions in model systems: design, control of catalytic activity and biosensor applications
Open this publication in new window or tab >>Protein-protein interactions in model systems: design, control of catalytic activity and biosensor applications
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes the design of polypeptides, unordered in the monomeric state but capable of folding into helix-loop-helix motifs and dimerise to form four-helix bundles. The goal of the design was to encode them with the capacity to form dimers highly selectively and the ability to carry out molecular functions in the folded state but not in the unordered state, and thus to establish a molecular link between recognition and function. The 42-residue sequences JR2E and JR2K were both shown by CD spectroscopy to adopt unordered conformations under single solute conditions at pH 7 but to form helical conformations in a 1:1 mixture. Analytical ultracentrifugation showed that JR2E and JR2K formed a clean heterodimer and the dissociation constant Kd, measured by CD spectroscopy, was found to be 5 ± 1 μM. Discrimination was enabled by the incorporation of charged residues at the dimer interface in the helical segments of the helix-loop-helix motif. Glutamic acids were incorporated in JR2E and lysines in JR2K, and charge repulsion prevented the monomeric subunits from forming homodimers. In mixtures, however, highly helical heterodimers were formed. The cooperative transition from unordered conformation to heterodimeric four-helix bundle was exploited in the design of a signal response system by incorporating a reactive site, capable of catalysing the hydrolysis of a m-nitrophenyl ester, into the negatively charged polypeptide. In the unfolded state the functionalised polypeptide was virtually inactive but in the folded state, induced by the interaction with JR2K, the substrate was hydrolysed approximately an order of magnitude more efficiently.

Interactions between the designed polypeptides and a functionalised polythiophene polymer were studied and it was found that the conformation of the polymer was controlled by the polypeptides, largely by electrostatic interactions. The negatively charged JR2E forced the polymer to adopt a planar conformation while the positively charged JR2K induced a more twisted conformation of the polymer. The spectral changes coupled to the conformational transitions of the polymer were used to measure the binding of human Carbonic anhydrase II by JR2E functionalised with a benzenesulphonamide ligand, in demonstration of its use as a tool for high-throughput screening.

JR2E immobilised on gold nanoparticles was shown to form homodimers reversibly under pH control, with affinities large enough to determine the state of aggregation of the gold nanoparticles.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1037
Keyword
Chemistry, Protein interactions, design, catalysis, biosensors, hybride materials, nanoparticles, Kemi
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-7485 (URN)91-85523-19-4 (ISBN)
Public defence
2006-09-22, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2009-04-01Bibliographically approved
2. Polypeptide-Based Nanoscale Materials
Open this publication in new window or tab >>Polypeptide-Based Nanoscale Materials
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Self-assembly has emerged as a promising technique for fabrication of novel hybrid materials and nanostructures. The work presented in this thesis has been focused on developing nanoscale materials based on synthetic de novo designed polypeptides. The polypeptides have been utilized for the assembly of gold nanoparticles, fibrous nanostructures, and for sensing applications.

The 42-residue polypeptides are designed to fold into helix-loop-helix motifs and dimerize to form four-helix bundles. Folding is primarily driven by the formation of a hydrophobic core made up by the hydrophobic faces of the amphiphilic helices. The peptides have either a negative or positive net charge at neutral pH, depending on the relative abundance of Glu and Lys. Charge repulsion thus prevents homodimerization at pH 7 while promoting hetero-dimerization through the formation of stabilising salt bridges. A Cys incorporated in position 22, located in the loop region, allowed for directed, thiol-dependent, immobilization on planar gold surfaces and gold nanoparticles. The negatively charged (Glu-rich) peptide formed homodimers and folded in solution at pH < 6 or in the presence of certain metal ions, such as Zn2+. The folding properties of this peptide were retained when immobilized directly on gold, which enabled reversible assembly of gold nanoparticles resulting in aggregates with well-defined interparticle separations. Particle aggregation was found to induce folding of the immobilized peptides but folding could also be utilized to induce aggregation of the particles by exploiting the highly specific interactions involved in both homodimerization and hetero-association. The possibility to control the assembly of polypeptide-functionalized gold nanoparticles was utilized in a colorimetric protein assay. Analyte binding to immobilized ligands prevented the formation of dense particle aggregates when subjecting the particles to conditions normally causing extensive aggregation. Analyte binding could hence easily be distinguished by the naked eye. Moreover, the peptides were utilized to assemble gold nanoparticles on planar gold and silica substrates.

Fibrous nanostructures were realized by linking monomers through a disulphide-bridge. The disulphide-linked peptides were found to spontaneously assemble into long and extremely thin peptide fibres as a result of a propagating association mediated by folding into four-helix bundles.

Abstract [en]

Ingenjörer och vetenskapsmän har ofta inspirerats av naturen i sökandet efter lösningar på tekniska problem. Allt ifrån byggnadskonstruktioner, flygplansvingar, kompositmaterial till kardborrebandet har skapats med utgångspunkt från förebilder i naturen. Många av de material och konstruktioner som återfinns i naturen har åtråvärda egenskaper som är svåra att erhålla i syntetiska matrial med traditionell teknik. Även om vi i flera fall kan härma sammansättningen och formen blir resultatet inte nödvändigtvis det samma. Den största skillnaden mellan syntetiska material och material producerade av levande organismer är hur deras komponenter sinsemellan är organiserade och sammansatta. I syntetiska material är komponenterna ofta inbördes mer eller mindre slumpvis ordnade medan de i biologiska material är organiserade med en oerhörd precision som sträcker sig ända ned på molekyl- och atomnivå. Naturens byggstenar har genom evolutionens gång förfinats för att spontant kunna organisera sig och bilda komplexa material  och strukturer. Denna process, som styrs genom att många svaga krafter inom och mellan byggstenarna samverkar, kallas ofta för självorganisering och är en förutsättning för allt liv. Självorganisering har också blivit en allt viktigare metod inom nanotekniken för att konstruera material och strukturer med nanometerprecision.

I den här avhandlingen beskrivs en typ av självorganiserande material där byggstenarna utgörs av nanometerstora guldpartiklar och syntetiska proteiner. De syntetiska proteinerna är designade för att efterlikna naturliga biomolekyler och antar en välbestämd tredimensionell struktur när två av dem interagerar med varandra. Denna interaktion är mycket specifik men kan styras genom att variera kemiska parametrar som surhet och jonstyrka vilket ger en möjlighet att påverka och kontrollera proteinernas struktur. Proteinerna har vidare modifierats för att spontant organisera sig till fibrer som är flera mikrometer långa men endast några nanometer tjocka. Proteinfibrer utgör en mycket viktig typ av strukturer i biologiska system och finns i alltifrån spindelväv till muskler. Syntetiska proteinfibrer är därför både ett intressant modellsystem och ett material med många potentiellt intressanta användningsområden.

Genom att fästa de syntetiska proteinerna på ytan av guldnanopartiklar går interaktionerna mellan partiklarna att kontrollera på samma sätt som interaktionerna mellan proteinerna. Krafterna mellan proteinerna och interaktionerna involverade i proteinernas veckning har använts för att reversibelt aggregera och organisera nanopartiklarna. Ett antal olika byggstenar har studerats och utvecklats till något som liknar ett mycket enkelt nano-Lego, som på en given signal spontant bygger ihop sig eller trillar isär.

Guldnanopartiklar är intressanta eftersom de är stabila och lätta att modifiera kemiskt men också på grund av deras optiska egenskaper som ger dem en ovanligt vacker vinröd färg. Färgen uppstår på grund av partiklarnas ringa storlek och varierar naturligt med egenskaperna hos den omgivande miljön. Detta gör det enkelt att studera hur partiklarna interagerar eftersom de byter färg när de närmar sig varandra, men gör dem också intressanta för sensortillämpningar. En enkel och robust sensor beskrivs i avhandlingen där syntetiska proteiner, speciellt utformade för att upptäcka och binda andra molekyler, har fästs på nanopartiklarna. Med partiklarnas hjälp går det att med blotta ögat detektera ett mänskligt protein i koncentrationer under ett tusendels gram per liter. En tidig diagnos av sjukdomstillstånd kan i de flesta fall avsevärt underlätta behandlingen och behovet av enkla sensorer för att bestämma närvaro och koncentration av medicinskt intressanta molekyler är därför mycket stort.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 74 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1207
Keyword
Gold nanoparticle, polypeptide, helix-loop-helix, four-helix bundle, self-assembly, folding
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:liu:diva-15124 (URN)978-91-7393-818-1 (ISBN)
Public defence
2008-10-03, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-10-16 Created: 2008-10-16 Last updated: 2014-10-08Bibliographically approved

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Aili, DanielEnander, KarinRydberg, JohanLundström, IngemarBaltzer, LarsLiedberg, Bo

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