Page 26 |
Save page Remove page | Previous | 26 of 185 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
10
adsorption of human and bovine serum albumin (HAS and BSA) on silica-titania
surfaces was found to be much slower in phosphate buffered saline (PBS) buffer
compared with adsorption in HEPES buffer 41. BSA adsorption on hydroxyapatite
(HAP) was found to be depressed by the presence of phosphate ions42. The structural
rearrangement of adsorbed Cytochrome C on graphite electrodes surface43 and
hematite surface6 was found to be efficiently suppressed with the presence of
phosphate ions. Due to the great variety of protein and surfaces studied, and the
complex solvent environment employed, no general conclusions or physical models
have been proposed. In order for reported experimental adsorption data to have
significance or relevance to actual applications (such as surface fouling due to protein
adsorption) and for meaningful comparisons to be made, the role of buffers in the
adsorption process must be understood and selection of buffer type and buffer
concentration must be made with care.
The objective of this chapter is to study the buffer effect on the protein
adsorption behavior. In this study, we chose Tris-HCl and PBS, two commonly used
buffers at physiological pH. The proteins considered include bovine serum albumin
(BSA), lysozyme, immunoglobulin G (IgG), and fibrinogen. These proteins have
different isoelectric points and are different in size and shape. The temperature was
fixed at 25 o C and the pH was kept at 7.4. We chose a simple uniform surface (Ge) so
that comparisons of data for different proteins and buffers can be made without
complications arising from surface heterogeneity, reproducibility of surface
morphology or surface changes as result of adsorption. The technique employed is
Object Description
| Title | Experimental study and atomic simulation of protein adsorption |
| Author | Wei, Tao |
| Author email | twei2004@gmail.com; dnaafm@yahoo.com.cn |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2008-07-29 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-07 |
| Advisor (committee chair) | Shing, Katherine |
| Advisor (committee member) |
Nakano, Aiichiro Goo, Edward K. |
| Abstract | The studies of protein adsorption at solid-liquid interface are important in various applications. Multilayer and irreversible adsorption behaviors are commonly observed. In this work, protein adsorption behavior at the solid-liquid interface was investigated by a combination of experimental Fourier transform infrared/attenuated total reflectance (FTIR/ATR) studies and computer simulations: Molecular Dynamics (MD) simulation and hybrid Genetic-Algorithm (GA) schemes.; BSA, lysozyme, IgG and fibrinogen adsorption was studied with FTIR/ATR in tris(hydroxymethyl)-aminomethane hydrochloride (Tris-HCl) and phosphate buffered saline (PBS) buffers on a Ge surface. Buffer choice was shown to drastically affect adsorption kinetics. In comparison with Tris-HCl, PBS buffer depresses the adsorption of BSA, IgG and fibrinogen in the prolonged quasi-linear kinetic region while lysozyme adsorption is relatively insensitive to buffer choice. Buffer concentration can also significantly affect protein adsorption. The secondary structures in the adsorbed phase are generally quite different from the bulk structure; however, buffer choice has negligible effect on structural evolution. Significant secondary structure changes occur during adsorption. The secondary structures in the adsorbed phase are inhomogeneous. The role of phosphate ions in PBS buffer and their effect on protein adsorption are rather complex. Phosphate ions adsorb competitively against protein molecules and their deprotonation equilibrium can be altered at the solid-liquid interface due to the adsorbed protein.; The effect of surface on adsorption is examined by adsorbing IgG on various polymer-coated surfaces. IgG adsorption is higher on more hydrophobic surface. IgG molecules adsorbed in layers near hydrophilic solid surfaces suffer less secondary structure changes.; The behavior of lysozyme during adsorption on a hydrogen-terminated Si surface (Si-H) is studied using MD simulations. Although atomistic simulations are highly time-consuming for direct observations of complete secondary structure changes, indications of molecular deformations are observed over nanosecond simulation time scale. Lysozyme molecule undergoes deformation onto the Si-H surface, as is evidenced by the reduction in the volume, the increase in solvent accessible surface area, the change of the overall shape, and certain amount of alteration in secondary structures. The main α-helix domains experience some loss while the beta-sheet domains remain almost intact. The hydrophobic character of the surface is believed to contribute to the loss of the organized structures of the amino residues in close proximity to the surface.; An efficient hybrid GA/spatial-grid method was developed to search for low adsorption-energy orientations and locations of a protein molecule on a solid surface. The surface and the protein molecule are treated as rigid bodies, whereas the bulk fluid is represented by spatial grids. The hybrid search procedure consists of two interlinked loops. In 1st loop (A), a GA is employed to identify promising regions for the global energy minimum, whereas a local optimizer with the derivative-free Nelder-Mead method is used to search for the lowest-energy orientation within the identified regions. In 2nd loop (B), new population is generated and competitive solution from loop A is improved. The switching between two loops is adaptively controlled by similarity analysis. We test the method for lysozyme adsorption on a hydrophobic Si-H (110) surface in implicit water. The hybrid search method was shown to have faster convergence and better solution accuracy compared with the conventional GA, which suffered from premature convergence. |
| Keyword | protein adsorption; FTIR/ATR; MD simulation; hybrid genetic algorithm |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1641 |
| Contributing entity | University of Southern California |
| Rights | Wei, Tao |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Wei-2367 |
| Archival file | uscthesesreloadpub_Volume14/etd-Wei-2367.pdf |
Description
| Title | Page 26 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 10 adsorption of human and bovine serum albumin (HAS and BSA) on silica-titania surfaces was found to be much slower in phosphate buffered saline (PBS) buffer compared with adsorption in HEPES buffer 41. BSA adsorption on hydroxyapatite (HAP) was found to be depressed by the presence of phosphate ions42. The structural rearrangement of adsorbed Cytochrome C on graphite electrodes surface43 and hematite surface6 was found to be efficiently suppressed with the presence of phosphate ions. Due to the great variety of protein and surfaces studied, and the complex solvent environment employed, no general conclusions or physical models have been proposed. In order for reported experimental adsorption data to have significance or relevance to actual applications (such as surface fouling due to protein adsorption) and for meaningful comparisons to be made, the role of buffers in the adsorption process must be understood and selection of buffer type and buffer concentration must be made with care. The objective of this chapter is to study the buffer effect on the protein adsorption behavior. In this study, we chose Tris-HCl and PBS, two commonly used buffers at physiological pH. The proteins considered include bovine serum albumin (BSA), lysozyme, immunoglobulin G (IgG), and fibrinogen. These proteins have different isoelectric points and are different in size and shape. The temperature was fixed at 25 o C and the pH was kept at 7.4. We chose a simple uniform surface (Ge) so that comparisons of data for different proteins and buffers can be made without complications arising from surface heterogeneity, reproducibility of surface morphology or surface changes as result of adsorption. The technique employed is |
