Advanced

Properties of Protein and Polymer Systems

Carlsson, Fredrik LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Proteiners interaktioner med andra proteiner, med polymerer och med ytor har stor praktisk betydelse inom bland annat proteinrening, läkemedelsformulering och livsmedelsteknologi. Målet med detta arbete är att öka förståelsen för växelverkan mellan proteiner, mellan proteiner och polymerer samt mellan proteiner och ytor, särskilt beträffande de elektrostatiska krafternas betydelse. Egenskaper som har studerats inkluderar enskilda proteinladdningars betydelse för strukturen hos bildade komplex i protein- och protein/polymer-system, samt fasbeteende.



Metoden som har använts här har huvudsakligen varit datorsimuleringar. Den använda Monte Carlo metoden kan jämföras med att filma... (More)
Popular Abstract in Swedish

Proteiners interaktioner med andra proteiner, med polymerer och med ytor har stor praktisk betydelse inom bland annat proteinrening, läkemedelsformulering och livsmedelsteknologi. Målet med detta arbete är att öka förståelsen för växelverkan mellan proteiner, mellan proteiner och polymerer samt mellan proteiner och ytor, särskilt beträffande de elektrostatiska krafternas betydelse. Egenskaper som har studerats inkluderar enskilda proteinladdningars betydelse för strukturen hos bildade komplex i protein- och protein/polymer-system, samt fasbeteende.



Metoden som har använts här har huvudsakligen varit datorsimuleringar. Den använda Monte Carlo metoden kan jämföras med att filma molekyler med en tänkt filmkamera och sedan klippa ihop scenerna slumpmässigt utan kronologisk ordning. Efter ett tag skapas dock en mening när olika medelväden beräknas under simuleringen. Med denna teknik har man en viss frihet att flytta partiklarna under simuleringen, vilket är en fördel när man gör simuleringar av system med stora molekyler. Som modellprotein för studien har proteinet lysozym valts, eftersom detta är ett litet och kompakt protein, vars struktur är mycket stabil under de flesta förhållanden. Dessutom är lysozym ett protein som studerats intensivt och det finns många experimentella studier att jämföra med. Proteinmodellen består av en hård sfär med positiva och negativa laddningar under ytan. Laddningarnas position har tagits från den tredimensionella strukturen för lysozym och projicerats på en sfär. Andra enklare proteinmodeller, som använts i tidigare datorsimuleringar, har ofta en jämnt fördelad laddning.



I det första steget har växelverkan mellan ett protein och en polymer undersökts. Vi fann att polymeren fördelade sig ojämnt över proteinets yta som ett resultat av de diskreta laddningarna och att en proteinmodell med diskreta laddningar gav mera polymer på proteinytan jämfört med en modell med jämnt fördelad laddning. I nästa steg undersöktes en lösning med många proteiner, och den icke-elektrostatiska interaktionen mellan proteinerna justerades efter experimentella data. I dessa simuleringar kunde till exempel jämviktskonstanter för lysozyms dimerisering reproduceras. I ett tredje steg jämfördes olika sätt att representera laddningarna i proteinet och två olika sätt att behandla små joner. Det förelåg en relativt liten skillnad mellan de olika laddningsrepresentationerna och skillnaden mellan de olika sätten att behandla joner var obetydlig vid låga jonkoncentrationer, men ökade som förväntat vid högre jonkoncentrationer. I en fjärde studie utvidgades systemet till att omfatta många proteiner och många polymerer. Vi kunde simulera den utfällning och återupplösning som observeras experimentellt då en laddad polymer i ökande koncentration blandas med en lösning av proteiner. Denna process återges på baksidan av omslaget. I ett sista simuleringsarbete undersöktes proteinmodellen vid en yta. Resultat från simuleringarna vid en yta stämde bra överens med experimentella studier exempelvis med avseende på hur mycket lysozym som adsorberar vid olika koncentrationer. Slutligen undersöktes interaktionen mellan polymeren poly(N-isopropyl-akrylamid) (pNIPAM) och andra ämnen, bland annat lysozym, samt adsorptionen av pNIPAM till en yta och det adsorberade skiktets temperaturberoende. (Less)
Abstract
Interactions of proteins with other proteins, with polymers and with surfaces are of great practical importance within for instance protein purification, drug delivery, and food technology. The aim of this work is to increase the understanding of protein-protein, protein-polyelectrolyte, and protein-surface interactions, particularly concerning the role of electrostatic interactions in these systems. Properties that have been studied include the role of discrete charges of the protein in protein self-association, complexation with a polyelectrolyte, and adsorption to a surface.



The main method used in the present investigation has been Monte Carlo simulation. Lysozyme was chosen as a model protein because of its high... (More)
Interactions of proteins with other proteins, with polymers and with surfaces are of great practical importance within for instance protein purification, drug delivery, and food technology. The aim of this work is to increase the understanding of protein-protein, protein-polyelectrolyte, and protein-surface interactions, particularly concerning the role of electrostatic interactions in these systems. Properties that have been studied include the role of discrete charges of the protein in protein self-association, complexation with a polyelectrolyte, and adsorption to a surface.



The main method used in the present investigation has been Monte Carlo simulation. Lysozyme was chosen as a model protein because of its high degree of structural stability under a variety of conditions and because of the large amount of experimental data available for comparison with the simulation results. The protein model consists of a hard sphere with positive and negative charges beneath the surface. The positions of the charges have been taken from the lysozyme crystal structure and projected on a sphere.



In the first study the interaction between one protein and one polymer was investigated. It was found that the polymer was distributed unevenly over the surface of the protein because of the discrete charges. Furthermore, it was found that the discrete-charge protein model gave a higher level of adsorbed polyelectrolyte than a model with uniformly distributed charge. In the second study, a solution with many proteins was investigated, and the short-range interaction between the proteins was adjusted according to experimental light scattering data. Simulation results on protein self-association agreed with previously reported results in the literature. In the third study, different ways to represent the charges of the protein and different ways to include the small ions were compared. There was a small difference between the different charge representations. The difference between the ion models was minute at low ionic strength and slightly larger at higher ionic strength. In a fourth study, the system was extended to many proteins and many polymers. We were able to simulate the precipitation and redissolution, which is observed experimentally when a charged polymer is added to a protein solution. In a final study, the protein model was investigated at a surface. Simulated adsorption isotherms as well as lateral radial distribution functions for adsorbed proteins agreed well with experimental data. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Dickinson, Eric
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Fysikalisk kemi, Physical chemistry, lysozyme, mica, surface, dimerization, precipitation, aggregate, cluster, complex, polyelectrolyte, protein, polymer
pages
156 pages
publisher
Fredrik Carlsson, YKI, Ytkemiska Institutet AB, Box 5607, SE-114 86 Stockholm, SWEDEN,
defense location
Lund
defense date
2002-10-31 10:15
ISBN
91-628-5372-4
language
English
LU publication?
yes
id
e4581875-bd3e-43ed-97bb-7145134babcd (old id 465095)
date added to LUP
2007-10-14 14:50:16
date last changed
2016-09-19 08:45:07
@misc{e4581875-bd3e-43ed-97bb-7145134babcd,
  abstract     = {Interactions of proteins with other proteins, with polymers and with surfaces are of great practical importance within for instance protein purification, drug delivery, and food technology. The aim of this work is to increase the understanding of protein-protein, protein-polyelectrolyte, and protein-surface interactions, particularly concerning the role of electrostatic interactions in these systems. Properties that have been studied include the role of discrete charges of the protein in protein self-association, complexation with a polyelectrolyte, and adsorption to a surface.<br/><br>
<br/><br>
The main method used in the present investigation has been Monte Carlo simulation. Lysozyme was chosen as a model protein because of its high degree of structural stability under a variety of conditions and because of the large amount of experimental data available for comparison with the simulation results. The protein model consists of a hard sphere with positive and negative charges beneath the surface. The positions of the charges have been taken from the lysozyme crystal structure and projected on a sphere.<br/><br>
<br/><br>
In the first study the interaction between one protein and one polymer was investigated. It was found that the polymer was distributed unevenly over the surface of the protein because of the discrete charges. Furthermore, it was found that the discrete-charge protein model gave a higher level of adsorbed polyelectrolyte than a model with uniformly distributed charge. In the second study, a solution with many proteins was investigated, and the short-range interaction between the proteins was adjusted according to experimental light scattering data. Simulation results on protein self-association agreed with previously reported results in the literature. In the third study, different ways to represent the charges of the protein and different ways to include the small ions were compared. There was a small difference between the different charge representations. The difference between the ion models was minute at low ionic strength and slightly larger at higher ionic strength. In a fourth study, the system was extended to many proteins and many polymers. We were able to simulate the precipitation and redissolution, which is observed experimentally when a charged polymer is added to a protein solution. In a final study, the protein model was investigated at a surface. Simulated adsorption isotherms as well as lateral radial distribution functions for adsorbed proteins agreed well with experimental data.},
  author       = {Carlsson, Fredrik},
  isbn         = {91-628-5372-4},
  keyword      = {Fysikalisk kemi,Physical chemistry,lysozyme,mica,surface,dimerization,precipitation,aggregate,cluster,complex,polyelectrolyte,protein,polymer},
  language     = {eng},
  pages        = {156},
  publisher    = {ARRAY(0xe58a008)},
  title        = {Properties of Protein and Polymer Systems},
  year         = {2002},
}