Proteins often carry an intrinsic electric dipole moment, which can interact with external electric fields and cause protein motion. Previous research has found that the orientation of small proteins in gas phase can be controlled in a static electric field. This effect is hoped to benefit applications such as single-particle imaging, and possibly other techniques involving proteins in electric fields. With the purpose of improving our understanding and modeling of protein orientation, this project investigated the scarcely explored quantum mechanical aspects of the process, namely the polarizability. Ground-state electronic structure simulations of three small model proteins, ubiquitin, Trp-cage and lysozyme, under the influence of electric fields were performed in vacuum. The electric dipole moments of the proteins were extracted from simulations with an applied electric field of strength 1 V/nm for varying angles, with respect to a body fixed reference frame. A Python program was written to analyze and visualize the results. The results point to a connection between the polarizability and the structure of the proteins, as well as size. Next a 3D rigid rotor model was developed using Mathematica in order to study the orientation dynamics classically in a simplified and time efficient way, with the possibility of including the previous quantum results. A comparison between a simulation of ubiquitin with and without polarizability concluded that the polarizability seems to have a damping effect on the orientation dynamics, at least for the initial conditions tested in this study. Further research is necessary to validate the model and perform statistical analysis of many simulations with varying initial conditions. / Proteiner bär ofta på ett inneboende elektriskt dipolmoment, som vid interaktion med externa elektriska fält och orsakar rörelse hos proteinerna. Tidigare studier har funnit att orienteringen av små proteiner i gasfas kan kontrolleras i ett statiskt elektriskt fält. Den effekten kan förhoppningsvis vara en fördel i tillämpningar såsom single-particle imaging, och eventuellt andra tekniker som innefattar proteiner i elektriska fält. I syftet att förbättra vår förståelse och modellering av protein-orientering, har detta projekt undersökt de föga utforskade kvantmekaniska aspekterna av processen, nämligen polariserbarheten. Kvant-baserade simuleringar av grundtillståndet av tre små proteiner, ubiquitin, Trp-cage och lysozym, under påverkan av elektriska fält utfördes i vakuum. Proteinernas elektriska dipolmoment extraherades från simuleringar med ett elektriskt fält med styrkan 1 V/nm för olika vinklar, med avseende på ett kroppsfixerat koordinatsystem. Ett Python-program skrevs för att analysera och visualisera resultaten. Resultaten tyder på att polariserbarheten beror på strukturen och storleken av proteinerna. Därefter utformades en stel-rotor-modell med hjälp av Mathematica för att studera prienteringen klassiskt på ett förenklat och tidseffektivt sätt, med möjligheten att inkludera de tidigare kvantmekaniska resultaten. En jämförelse mellan en simulering av ubiquitin med och utan polariserbarhet konstaterade att polariserbarheten verkar ha en dämpande effekt på orienteringen, åtminstone för begynnelsevillkoren som testades i denna studie. Vidare forskning krävs för att styrka modellen och utföra statistisk analys av många simuleringar med varierande begynnelsevillkor.

<p>The objective of this thesis was to investigate and characterize the interaction between blood proteins and different surfaces with emphasis on protein adsorption to bioceramics and model surfaces. Special effort was made to monitor the spontaneous and selective adsorption of proteins from human plasma and to examine the orientation, conformation and functional behavior of single proteins after adsorption. </p><p>Five different ceramic biomaterials: alumina (Al₂O₃), zirconia (ZrO₂), hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and two glass-ceramics, AP40 (SiO₂-CaO-Na₂O-P₂O₅-MgO-K₂O-CaF₂) and RKKP (AP40 with Ta₂O₃-La₂O₃), were exposed to human plasma and their protein binding capacities and affinities for specific proteins were studied by chromatography, protein assays, two-dimensional gel electrophoresis and Western blotting. The studies showed that all materials adsorbed approximately the same high amount of plasma proteins and that they therefore should be fully covered by proteins in an <i>in vivo</i> setting. The adsorbed proteins were different for most materials which could explain their previously observed different levels of tissue integration <i>in vivo</i>. </p><p>Four of the proteins that behaved differently, ceruloplasmin, prothrombin, α₂-HS-glycoprotein and α₁-antichymotrypsin, were selected for characterization with atomic force microscopy and ellipsometry. The studies, which were performed on ultraflat silicon wafers (silica), showed that the proteins oriented themselves with their long axis parallel to the surface or as in case of ceruloplasmin with one of its larger sides towards the surface. All of them had globular shapes but other conformational details were not resolved. Furthermore, prothrombin (none of the others) formed multilayers at high proteins concentrations. </p><p>The functional behaviour of the adsorbed proteins, referring to their cell binding and cell spreading capacity on silica and a positive cell adhesion reference surface (Thermanox®), was affected by the underlying substrate. Ceruloplasmin, α₂-HS-glycoprotein and α₁-antichymotrypsin stimulated cell attachment to silica, but suppressed attachment to Thermanox®. Prothrombin stimulated cell attachment to both surfaces. The attachment was in most cases mediated both by cell membrane-receptors (integrins) and by non-specific interactions between the cell and the material. </p><p>This thesis showed that the compositional mixture, orientation, conformation and functional behavior of the adsorbed proteins are determined by the properties of the underlying surface and if these parameters are controlled very different cellular responses can be induced.</p>

The objective of this thesis was to investigate and characterize the interaction between blood proteins and different surfaces with emphasis on protein adsorption to bioceramics and model surfaces. Special effort was made to monitor the spontaneous and selective adsorption of proteins from human plasma and to examine the orientation, conformation and functional behavior of single proteins after adsorption. Five different ceramic biomaterials: alumina (Al2O3), zirconia (ZrO2), hydroxyapatite (Ca10(PO4)6(OH)2) and two glass-ceramics, AP40 (SiO2-CaO-Na2O-P2O5-MgO-K2O-CaF2) and RKKP (AP40 with Ta2O3-La2O3), were exposed to human plasma and their protein binding capacities and affinities for specific proteins were studied by chromatography, protein assays, two-dimensional gel electrophoresis and Western blotting. The studies showed that all materials adsorbed approximately the same high amount of plasma proteins and that they therefore should be fully covered by proteins in an in vivo setting. The adsorbed proteins were different for most materials which could explain their previously observed different levels of tissue integration in vivo. Four of the proteins that behaved differently, ceruloplasmin, prothrombin, α2-HS-glycoprotein and α1-antichymotrypsin, were selected for characterization with atomic force microscopy and ellipsometry. The studies, which were performed on ultraflat silicon wafers (silica), showed that the proteins oriented themselves with their long axis parallel to the surface or as in case of ceruloplasmin with one of its larger sides towards the surface. All of them had globular shapes but other conformational details were not resolved. Furthermore, prothrombin (none of the others) formed multilayers at high proteins concentrations. The functional behaviour of the adsorbed proteins, referring to their cell binding and cell spreading capacity on silica and a positive cell adhesion reference surface (Thermanox®), was affected by the underlying substrate. Ceruloplasmin, α2-HS-glycoprotein and α1-antichymotrypsin stimulated cell attachment to silica, but suppressed attachment to Thermanox®. Prothrombin stimulated cell attachment to both surfaces. The attachment was in most cases mediated both by cell membrane-receptors (integrins) and by non-specific interactions between the cell and the material. This thesis showed that the compositional mixture, orientation, conformation and functional behavior of the adsorbed proteins are determined by the properties of the underlying surface and if these parameters are controlled very different cellular responses can be induced.