Soonwoo Chah

Surface plasmon resonance study of vesicle rupture by virus-mimetic attack

Frank and coworkers [N. J. Cho, S. J. Cho, K. H. Cheong, J. S. Glenn and C. W. Frank, J. Am. Chem. Soc., 2007, 129, 10050] investigated what happens when lipid vesicles made of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), which serves as a mimic for cell membranes, are exposed to the amphipathic helix peptide, PEP1, which is of the same type found in hepatitis C virus. Using atomic force field microscopy and quartz crystal microbalance measurements they presented evidence that the vesicle is transformed into a lipid bilayer. We use surface plasmon resonance (SPR) microscopy to follow this process in real time. We find an induction period (intermediate state) of approximately 10-min duration between the time of membrane binding and membrane rupture. The SPR data support the interpretation that a lipid bilayer is formed and allow us to put forward a mechanism for the vesicle-rupture event. As a side benefit, we demonstrate how to build two-dimensional lipid patterns on a gold surface using this vesicle-rupture process.

Folding Control and Unfolding Free Energy of Yeast Iso-1-cytochrome c Bound to Layered Zirconium Phosphate Materials Monitored by Surface Plasmon Resonance

The free energy change (Delta G degrees ) for the unfolding of immobilized yeast iso-1-cytochrome c (Cyt c) at nanoassemblies was measured by surface plasmon resonance (SPR) spectroscopy. Data show that SPR is sensitive to protein conformational changes, and protein solid interface exerts a major influence on bound protein stability. First, Cyt c was self-assembled on the Au film via the single thiol of Cys-102. Then, crystalline sheets of layered alpha-Zr(O(3)POH)(2).H(2)O (alpha-ZrP) or Zr(O(3)PCH(2)CH(2)COOH)(2).xH(2)O (alpha-ZrCEP) were adsorbed to construct alpha-ZrP/Cyt c/Au or alpha-ZrCEP/Cyt c/Au nanoassemblies. The construction of each layer was monitored by SPR, in real time, and the assemblies were further characterized by atomic force microscopy and electrochemical studies. Thermodynamic stability of the protein nanoassembly was assessed by urea-induced unfolding. Surprisingly, unfolding is reversible in all cases studied here. Stability of Cyt c in alpha-ZrP/Cyt c/Au increased by approximately 4.3 kJ/mol when compared to the unfolding free energy of Cyt c/Au assembly. In contrast, the protein stability decreased by approximately 1.5 kJ/mol for alpha-ZrCEP/Cyt c/Au layer. Thus, OH-decorated surfaces stabilized the protein whereas COOH-decorated surfaces destabilized it. These data quantitate the role of specific functional groups of the inorganic layers in controlling bound protein stability.