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15
sensitive to many parameters such as bulk protein concentration, protein molecular
shape, molecular size and flexibility as well as protein/surface interactions, among
others. Table 2.1 shows our estimates made by assuming closed pack coverage of the
protein molecule and applying the jamming limit (approximately 50% for many
common shaped objects45). IgG, fibrinogen, and lysozyme protein molecules are
treated as ellipsoids, while BSA is modeled as a triangular prismatic shell46 with
molecular dimensions shown in Table 2.1. In estimating the molecular packing, we
assumed half of protein molecules adsorbed are lying flat at the maximum projected
area and the other half are standing at the minimum projected area. With these
assumptions, the estimated mass per adsorbed layer for BSA is 2.0 mg/m2, which is
comparable to the reported experimental saturation adsorption value (1.8-2.4
mg/m2)45,47. The estimated mass per adsorbed layer for IgG is 4.9mg/m2, which is
within the reported experimental range of 2.1-8.4 mg/m2 depending on the
experimental conditions 45. The estimated mass per adsorbed layer for fibrinogen is
5.5 mg/m2, which is comparable to the reported experimental saturation adsorption
value of 5 mg/m2 on tantalum film48. The estimated mass per adsorbed layer for
lysozyme is 1.5 mg/m2, which is comparable to the experimental range of
0.95-2.1mg/m2 reported on silica surface11 and 1.7 mg/m2 on SiO2 surface49. We
emphasize that the values shown in Table 2.1 are approximations and are used only to
aid visualization of the adsorbed phase.
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 31 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 15 sensitive to many parameters such as bulk protein concentration, protein molecular shape, molecular size and flexibility as well as protein/surface interactions, among others. Table 2.1 shows our estimates made by assuming closed pack coverage of the protein molecule and applying the jamming limit (approximately 50% for many common shaped objects45). IgG, fibrinogen, and lysozyme protein molecules are treated as ellipsoids, while BSA is modeled as a triangular prismatic shell46 with molecular dimensions shown in Table 2.1. In estimating the molecular packing, we assumed half of protein molecules adsorbed are lying flat at the maximum projected area and the other half are standing at the minimum projected area. With these assumptions, the estimated mass per adsorbed layer for BSA is 2.0 mg/m2, which is comparable to the reported experimental saturation adsorption value (1.8-2.4 mg/m2)45,47. The estimated mass per adsorbed layer for IgG is 4.9mg/m2, which is within the reported experimental range of 2.1-8.4 mg/m2 depending on the experimental conditions 45. The estimated mass per adsorbed layer for fibrinogen is 5.5 mg/m2, which is comparable to the reported experimental saturation adsorption value of 5 mg/m2 on tantalum film48. The estimated mass per adsorbed layer for lysozyme is 1.5 mg/m2, which is comparable to the experimental range of 0.95-2.1mg/m2 reported on silica surface11 and 1.7 mg/m2 on SiO2 surface49. We emphasize that the values shown in Table 2.1 are approximations and are used only to aid visualization of the adsorbed phase. |
