Structure and mechanism of peptide-induced membrane pores
| dc.contributor.advisor | Huang, Huey W. | |
| dc.creator | Qian, Shuo | |
| dc.date.accessioned | 2011-07-25T01:38:33Z | |
| dc.date.available | 2011-07-25T01:38:33Z | |
| dc.date.issued | 2009 | |
| dc.description.abstract | This thesis reports the studies of the structure and mechanism of peptide-induced membrane pores by antimicrobial peptide alamethicin and by a peptide named Baxalpha5, which is derived from Bax protein. Alamethicin is one of best known antimicrobial peptides, which are ubiquitous throughout the biological world. Bax-alpha5 peptide is the pore-forming domain of apoptosis regulator protein Bax, which activates pore formation on outer mitochondrial membrane to release cytochrome c to initiate programmed cell death. Both peptides as well as many other pore-forming peptides, induce pores in membrane, however the structure and mechanism of the pore formation were unknown. By utilizing grazing angle x-ray diffraction, I was able to reconstruct the electron density profile of the membrane pores induced by both peptides. The fully hydrated multiple bilayers of peptide-lipid mixture on solid substrate were prepared in the condition that pores were present, as established previously by neutron in-plane scattering and oriented circular dichroism. At dehydrated conditions, the inter bilayer distance of the sample shortened and the interactions between bilayers caused the membrane pores to become long-ranged correlated and formed a periodically ordered lattice of rhombohedral symmetry, so that x-ray diffraction can be applied. To help solving the phase problem of diffraction, a brominated lipid was used and multi-wavelength anomalous diffraction was performed below the bromine K-edge. The reconstructed electron density profiles unambiguously revealed that the alamethicin-induced membrane pore is of barrel-stave type, while the Bax-alpha5 induced pore is of lipidic toroidal (wormhole) type. The underlying mechanism of pore formation was resolved by observing the time-dependent process of pore formation in vesicles exposed to Bax-alpha5 solutions, as well as the membrane thinning experiment. This demonstrated that Bax-alpha5 exhibited the same sigmoidal concentration dependence as alamethicin: below a threshold concentration, peptide only binds to membrane surface, and thins the membrane; when the concentration exceeds a critical value, pores are formed. The structure and mechanism of peptide-induced membrane pores provide insight onto how alpha-pore-forming proteins and peptides interact with membrane. The results also suggest that formation of lipidic pores is the major mechanism for alpha-pore-forming proteins. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.callno | THESIS SP. SCI. 2009 QIAN | |
| dc.identifier.citation | Qian, Shuo. "Structure and mechanism of peptide-induced membrane pores." (2009) Diss., Rice University. <a href="https://hdl.handle.net/1911/61836">https://hdl.handle.net/1911/61836</a>. | |
| dc.identifier.uri | https://hdl.handle.net/1911/61836 | |
| dc.language.iso | eng | |
| dc.rights | Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder. | |
| dc.subject | Biochemistry | |
| dc.subject | Physics | |
| dc.subject | Biophysics | |
| dc.title | Structure and mechanism of peptide-induced membrane pores | |
| dc.type | Thesis | |
| dc.type.material | Text | |
| thesis.degree.department | Space Science | |
| thesis.degree.discipline | Natural Sciences | |
| thesis.degree.grantor | Rice University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |
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