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52
2.4 Conclusions
Buffer type as well as buffer concentration can have significant effect on protein
adsorption. In this work, we showed that PBS significantly depressed BSA, IgG and
fibrinogen adsorption on Ge at pH 7.4 compared to Tris-HCl. Lysozyme adsorption is
not significantly affected by buffer choice. A possible explanation is that phosphate
ions have a tendency to adsorb on the Ge surface making the surface negatively
charged, resulting in suppression of the adsorption of proteins carrying net negative
charge (at pH=7.4, BSA, IgG and fibrinogen are negatively charged whereas
lysozyme is positively charged). This sensitivity to buffer type and buffer
concentration means that care must be exercised when selecting the buffer conditions
for adsorption studies and when evaluating biomedical implants as well as when
comparing adsorption data. Protein secondary structures can change significantly
upon adsorption, however, buffer choice seems to have negligible effect on the
secondary structures of the adsorbed proteins studied here provided comparisons are
based on adsorbed amount rather than on adsorption time. The adsorption rate in the
multilayer region is proposed as the chemical potential control by the experiment
evidence of the linear relationship between the adsorption rate and the logarithm of
bulk concentration.
The behavior of PBS buffer, the most commonly used buffer at physiological pH,
is particularly complex in adsorption studies due to the various types of phosphate
ions present and the tendency of these ions to adsorb competitively and/or to form
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 68 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 52 2.4 Conclusions Buffer type as well as buffer concentration can have significant effect on protein adsorption. In this work, we showed that PBS significantly depressed BSA, IgG and fibrinogen adsorption on Ge at pH 7.4 compared to Tris-HCl. Lysozyme adsorption is not significantly affected by buffer choice. A possible explanation is that phosphate ions have a tendency to adsorb on the Ge surface making the surface negatively charged, resulting in suppression of the adsorption of proteins carrying net negative charge (at pH=7.4, BSA, IgG and fibrinogen are negatively charged whereas lysozyme is positively charged). This sensitivity to buffer type and buffer concentration means that care must be exercised when selecting the buffer conditions for adsorption studies and when evaluating biomedical implants as well as when comparing adsorption data. Protein secondary structures can change significantly upon adsorption, however, buffer choice seems to have negligible effect on the secondary structures of the adsorbed proteins studied here provided comparisons are based on adsorbed amount rather than on adsorption time. The adsorption rate in the multilayer region is proposed as the chemical potential control by the experiment evidence of the linear relationship between the adsorption rate and the logarithm of bulk concentration. The behavior of PBS buffer, the most commonly used buffer at physiological pH, is particularly complex in adsorption studies due to the various types of phosphate ions present and the tendency of these ions to adsorb competitively and/or to form |
