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POLYPEPTIDES - STRUCTURES AND INTERACTIONS IN MONOLAYERS AND AQUEOUS SOLUTIONS

Sjögren, Helen LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

Proteiner, eller äggviteämnen som de också kallas, har viktiga funktioner i kroppen. Proteiner är uppbyggda som långa, ofta sammanveckade kedjor. Byggstenarna i dessa kedjor kallas aminosyror. Ett givet protein kännetecknas av sin unika aminosyrekombination och ofta ingår flera av de 20, i människan förekommande, aminosyrorna i ett protein. I kroppen finns också kortare aminosyrakedjor, som kallas peptider. Det är viktigt att öka förståelsen för hur peptider och proteiner beter sig i kroppen. När peptider och proteiners omgivning förändras kan också deras form (deras s.k. struktur eller konformation) förändras. Strukturförändringar hos peptider och proteiner kan orsaka sjukdomar som Alzheimers,... (More)
Popular Abstract in Swedish

Proteiner, eller äggviteämnen som de också kallas, har viktiga funktioner i kroppen. Proteiner är uppbyggda som långa, ofta sammanveckade kedjor. Byggstenarna i dessa kedjor kallas aminosyror. Ett givet protein kännetecknas av sin unika aminosyrekombination och ofta ingår flera av de 20, i människan förekommande, aminosyrorna i ett protein. I kroppen finns också kortare aminosyrakedjor, som kallas peptider. Det är viktigt att öka förståelsen för hur peptider och proteiner beter sig i kroppen. När peptider och proteiners omgivning förändras kan också deras form (deras s.k. struktur eller konformation) förändras. Strukturförändringar hos peptider och proteiner kan orsaka sjukdomar som Alzheimers, Parkinsons och galna kosjukan.



Eftersom peptider och proteiner är komplicerade och består av så många olika byggstenar (aminosyror) kan det vara svårt att förstå hur olika faktorer i omgivningen påverkar deras struktur. Det kan då vara en fördel att studera enklare ämnen, t.ex. så kallade polyaminosyror. Även dessa är uppbyggda som långa kedjor av aminosyror, men med bara en eller två olika aminosyror som byggstenar. I de studier som presenteras i den här avhandlingen har den här typen av enkelt uppbyggda molekyler använts.



Olika aminosyror har olika egenskaper. En del är olösliga i vatten (hydrofoba aminosyror), medan andra löser sig väl i vatten (hydrofila aminosyror). Vissa hydrofila aminosyror är laddade (positivt eller negativt). Genom att ändra egenskaper (t.ex. pH) hos omgivningen kan dessa aminosyror gå från att vara laddade till att vara oladdade (eller tvärtom).



I den här avhandlingen presenteras resultat både från studier av hydrofoba polyaminosyror, som lägger sig på vattenytor utan att lösa sig i vattnet, och mer hydrofila sådana i olika vattenlösningar.



Vissa peptider och polyaminosyror kan fås att bilda spiralformade, styva strukturer (s.k. a helixar), som mest kan liknas vid långa, smala stavar. De stavar som används i studierna i den här avhandlingen är ungefär 18 miljondels millimeter långa och två miljondels millimeter i diameter. Det går att få dessa stavar att lägga sig i ett extremt tunt lager på vattenytan. Lagret kan fås att bara bli en molekyl tjockt. Genom att förändra vattenlösningen, t.ex. genom att ändra pH eller salthalt, kan stavarna på ytan fås att orientera sig på olika sätt. Detta kan liknas vid beteendet hos flytande kristallina displayer, som finns t.ex. i miniräknare och digitalklockor. Displayerna i dessa består av små ministavar som fås att ordna sig på olika sätt (och då visa olika siffror) genom att ström skickas genom displayen.



I arbetet som presenteras i den här avhandlingen har även hydrofila polyaminosyror i vattenösningar studerats. De har då blandats med olika tensider. Tensider är en sorts molekyler som har en (hydrofil) del som löser sig i vatten och en (hydrofob) del som skyr vatten, men löser sig i olja. Om dessa blandas med vatten bildar de små aggregat (s.k. miceller) med den vattenlösliga delen av tensidmolekylerna riktad utåt och den vattenskyende delen i mitten. I mitten av tensidaggregaten kan vattenolösliga ämnen lösas. Det är denna egenskap hos tensider som utnyttjas i rengöringsprodukter som tvål, schampo, disk- och tvättmedel. Alla dessa produkter består till största delen av tensider som kan få fett och annan smuts att lösa sig och lossa från kläder, disk eller hud och hår och sedan sköljas bort med tvättvattnet.



Tensider kan öka vattenlösligheten hos olika peptider och polyaminosyror, men kan också förändra konformationen hos dem. Detta kan ha betydelse både för att förhindra sjukliga konformationsförändringar, som de som sker vid Alzheimers sjukdom eller galna kosjukan, men också för att öka stabiliteten hos vissa läkemedel. Både den ökade vattenlösningen och konformationsförändringar hos polyaminosyror vid tensidtillsats har studerats i arbetet som presenteras i denna avhandling. (Less)
Abstract
The aim of this thesis work is to understand and be able to control polypeptide conformation and interactions at interfaces and in solution by changing the solution conditions. For this purpose simple model polypeptides, so-called polyamino acids, have been investigated at the air-liquid interface, as well as in aqueous solutions. The influence of subphase characteristics, spreading solvent and polypeptide molecular weight on the film morphology and molecular conformation have been investigated for polypeptide monolayers of a number of different polypeptides. The studies have been conducted by surface film balance experiments combined with circular (CD) and linear (LD) dichroism spectroscopy and atomic force microscopy (AFM) on monolayers... (More)
The aim of this thesis work is to understand and be able to control polypeptide conformation and interactions at interfaces and in solution by changing the solution conditions. For this purpose simple model polypeptides, so-called polyamino acids, have been investigated at the air-liquid interface, as well as in aqueous solutions. The influence of subphase characteristics, spreading solvent and polypeptide molecular weight on the film morphology and molecular conformation have been investigated for polypeptide monolayers of a number of different polypeptides. The studies have been conducted by surface film balance experiments combined with circular (CD) and linear (LD) dichroism spectroscopy and atomic force microscopy (AFM) on monolayers deposited with the Langmuir-Blodgett (LB) technique. Polypeptides spread from water soluble spreading solvents have been shown to aggregate at the air-water interface. This type of aggregation easily lead to misinterpretations of experimental data and probably accounts for inconsistencies of previously published reports on the conformation of polypeptides at interfaces.A method to determine the polypeptide secondary structure in films comprising laterally orientated polypeptide strands has been developed. Lateral orientation, as observed in CD spectroscopy, has been used as a tool to study the surface arrangement of all-helical polypeptide rods. Even for long polypeptides, consisting only of aliphatic amino acid residues, subphase characteristics (e.g. pH and salt) was shown to affect the surface lateral polypeptide arrangement. This amply demonstrates a surprisingly large influence of end-group charges on the inter-molecular ordering in polypeptide films. The pH induced conformational transition from alpha-helix to random coil of titrating polypeptides has been studied both at the air-liquid interface and in solution. The results show that the transition at the air-water interface is shifted around two pH units towards lower pH, as compared with the transition in solution. In the investigations of the helix-coil transition in solution, both experimental studies (by CD spectroscopy) and theoretical calculations have been performed. The helix-coil transition in two different lysine-containing polypeptides displayed an unexpected salt dependence in the transition region, where an increase of the ionic strength was found to lead to a decreased fraction of polypeptide in alpha-helix conformation.In addition, the interactions between polypeptides and non-ionic surfactants have been investigated, mainly utilising CD spectroscopy, NMR and surfactant binding isotherms. It was concluded that the mutual interaction between charged polypeptides and non-ionic surfactants can be used to tune the conformation of the polypeptide in solution: 1) A certain degree of polypeptide hydrophobicity was shown to be essential in order to obtain a stabilisation of the alpha-helical conformation upon surfactant addition. 2) Surfactants with small head groups and a propensity to form spherical or nearly spherical micelles (i.e. surfactants with low values of the critical packing parameter) yielded the most efficient stabilisation of alpha-helix. The polypeptide-surfactant complex can best be described by a necklace model, with surfactant micelles formed on the polypeptide chain with the hydrophobic polypeptide side chains interacting with the hydrophobic micellar core and the inner part of the surfactant head group. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Kinnunen, Paavo K. J., Biomedicinska institutionen, Helsingfors Universitet, Finland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Physical chemistry, Fysikalisk kemi, tyrosine), co-poly-L (lysine, phenylalanine), co-poly-L-(lysine, poly-L-glutamate, poly-L-lysine, poly-L-valine, poly-L-isoleucine, poly-gamma-methyl-L-glutamate, poly-L-leucine, monolayer, Langmuir-Blodgett film, CD spectroscopy, random coil, alpha-helix, surfactant stabilisation, polypeptide, polyamino acid
pages
220 pages
publisher
KF Sigma AB, Lund
defense location
Kemicentrum, K:B
defense date
2005-09-09 10:30
ISBN
91-7422-091-8
language
English
LU publication?
yes
id
f37fba47-5aa3-4130-b608-2633dd4fe42b (old id 545182)
date added to LUP
2007-10-13 13:10:34
date last changed
2016-09-19 08:45:05
@phdthesis{f37fba47-5aa3-4130-b608-2633dd4fe42b,
  abstract     = {The aim of this thesis work is to understand and be able to control polypeptide conformation and interactions at interfaces and in solution by changing the solution conditions. For this purpose simple model polypeptides, so-called polyamino acids, have been investigated at the air-liquid interface, as well as in aqueous solutions. The influence of subphase characteristics, spreading solvent and polypeptide molecular weight on the film morphology and molecular conformation have been investigated for polypeptide monolayers of a number of different polypeptides. The studies have been conducted by surface film balance experiments combined with circular (CD) and linear (LD) dichroism spectroscopy and atomic force microscopy (AFM) on monolayers deposited with the Langmuir-Blodgett (LB) technique. Polypeptides spread from water soluble spreading solvents have been shown to aggregate at the air-water interface. This type of aggregation easily lead to misinterpretations of experimental data and probably accounts for inconsistencies of previously published reports on the conformation of polypeptides at interfaces.A method to determine the polypeptide secondary structure in films comprising laterally orientated polypeptide strands has been developed. Lateral orientation, as observed in CD spectroscopy, has been used as a tool to study the surface arrangement of all-helical polypeptide rods. Even for long polypeptides, consisting only of aliphatic amino acid residues, subphase characteristics (e.g. pH and salt) was shown to affect the surface lateral polypeptide arrangement. This amply demonstrates a surprisingly large influence of end-group charges on the inter-molecular ordering in polypeptide films. The pH induced conformational transition from alpha-helix to random coil of titrating polypeptides has been studied both at the air-liquid interface and in solution. The results show that the transition at the air-water interface is shifted around two pH units towards lower pH, as compared with the transition in solution. In the investigations of the helix-coil transition in solution, both experimental studies (by CD spectroscopy) and theoretical calculations have been performed. The helix-coil transition in two different lysine-containing polypeptides displayed an unexpected salt dependence in the transition region, where an increase of the ionic strength was found to lead to a decreased fraction of polypeptide in alpha-helix conformation.In addition, the interactions between polypeptides and non-ionic surfactants have been investigated, mainly utilising CD spectroscopy, NMR and surfactant binding isotherms. It was concluded that the mutual interaction between charged polypeptides and non-ionic surfactants can be used to tune the conformation of the polypeptide in solution: 1) A certain degree of polypeptide hydrophobicity was shown to be essential in order to obtain a stabilisation of the alpha-helical conformation upon surfactant addition. 2) Surfactants with small head groups and a propensity to form spherical or nearly spherical micelles (i.e. surfactants with low values of the critical packing parameter) yielded the most efficient stabilisation of alpha-helix. The polypeptide-surfactant complex can best be described by a necklace model, with surfactant micelles formed on the polypeptide chain with the hydrophobic polypeptide side chains interacting with the hydrophobic micellar core and the inner part of the surfactant head group.},
  author       = {Sjögren, Helen},
  isbn         = {91-7422-091-8},
  keyword      = {Physical chemistry,Fysikalisk kemi,tyrosine),co-poly-L (lysine,phenylalanine),co-poly-L-(lysine,poly-L-glutamate,poly-L-lysine,poly-L-valine,poly-L-isoleucine,poly-gamma-methyl-L-glutamate,poly-L-leucine,monolayer,Langmuir-Blodgett film,CD spectroscopy,random coil,alpha-helix,surfactant stabilisation,polypeptide,polyamino acid},
  language     = {eng},
  pages        = {220},
  publisher    = {KF Sigma AB, Lund},
  school       = {Lund University},
  title        = {POLYPEPTIDES - STRUCTURES AND INTERACTIONS IN MONOLAYERS AND AQUEOUS SOLUTIONS},
  year         = {2005},
}