John C. Conboy
ANALYTICAL & PHYSICAL CHEMISTRY OF BIOLOGICAL SURFACES
B.S. University of California, Davis, 1991
Phone: (801) 585-7957
Office: 2532 HEB-S
We are interested in development and application of novel analytical and bioanalytical techniques for the exploration of interfacial phenomena, such as protein adsorption, phase segregation in lipid membranes and ion transport between immiscible liquids. Our laboratory uses a combination of nonlinear optical spectroscopies in conjunction with biological and electrochemical methods to achieve these objectives.
Measuring the Conformation of Surface Confined Proteins. Chirality is a fundamental construct in nature, based on the antisymmetric arrangement of atoms, molecules or extended structures in such a way as to produce non- superimposable mirror images. Chirality plays an important role in the function of many molecules particularly biomolecules. The ability to retrieve information on surface chirality cannot be achieved with conventional linear spectroscopic methods. However, second-order nonlinear spectroscopies, such as surface second harmonic generation (SHG), possess the requisite surface selectivity and sensitivity to detect chirality. The interaction of proteins with surfaces affects everything from the functioning of biosensors to cell signaling. Of particular interest to our laboratory is the interaction of proteins with lipid membranes. In order to decipher the secondary structure of proteins at interfaces two nonlinear laser optical spectroscopies are employed; sum-frequency vibrational spectroscopy and chiral second harmonic generation (C-SHG). With the current lack of crystallographic and NMR data available on the structure of surface confined proteins, the goal of the research is to develop new analytical tools for conformational analysis of proteins at interfaces.
Lipid Flip-Flop and the Role of Proteins, Cholesterol and Membrane Defects Understanding the movement of lipid species across the cellular membrane is a fundamental goal in molecular biology. Since the biosynthesis of phospholipids is generally confined to the cytosolic leaflet of a membrane, the continual growth of cells requires the alteration of the outer membrane by the translocation of phospholipids. It has been hypothesized that lipid transbilayer migration is a protein-mediated process. However, a putative protein "flipase" has yet to be definitively identified. We are using a novel application of sum-frequency vibrational spectroscopy (SFVS) developed to selectively probe the asymmetry in a planar-supported lipid bilayer (PSLB). This new spectroscopic approach allows for the direct detection of lipid flip-flop without the need for a fluorescent or spin-labeled lipid probe, which can alter the measured translocation rates. The goal of this research is to address some of the central issues concerning the transbilayer movement of lipids. These include the effect of phospholipid fatty acid alkyl chain length and saturation on the rate of flip-flop, and the effect of headgroup chemistry and charge on lipid migration. In addition, the role non-lipid constituents play on the movement of phospholipids, in particular cholesterol and transmembrane peptides, are also being explored.
Chiral Imaging for High-Throughput Proteome Screening The use of microarray -based protein assays has the potential to dramatically increase the analysis of global protein populations within living organisms. The practical implementation of these technologies will have a significant impact in proteomics, the pharmacological screening of drug candidates, and the investigation of protein-protein interactions. Most conventional microarray-based strategies for detecting protein-ligand and protein-protein associations are based on fluorescence methods to visualize the interaction of interest.
Such methodologies require the fluorescent labeling of a large population of proteins with fluorophores. The inability to accurately perform this operation in a controlled manner for the complete protein output of a cell or organism is a major drawback to currently proposed techniques for high throughput protein screening. We are developing techniques which use the intrinsic chirality of proteins to "image" their association on patterned microarrays. Our research efforts in the area represent a novel experimental approach that should provide answers to a growing number of questions concerning detection for high throughput proteome screening.
Imaging Structure in the "Fluid Mosaic" of Cell Membranes: Cholesterol is a major constituent of biological membranes in mammalian cells, but its effect on the physical properties of lipid systems is still not well understood. In cell membranes, cholesterol is responsible for maintaining the fluid state of the lipid matrix. Recent evidence suggests that cholesterol might facilitate the formation of "rafts" or regions of distinct lipid composition or structure. These domains are believed to be necessary for cellular process such as extra-cellular signaling and immune response. The goal of our research is to visualize these distinct domains with the use of novel nonlinear microscopies.
Room Temperature Liquid Salts for Use in Aqueous Extractions: Room temperature ionic liquids (RTILs), which are air stable and immiscible with water, have been touted as novel solvents for organic/inorganic reactions and environmentally friendly alternatives for liquid-liquid extractions. Advances in the area of solvent and metal ion extraction utilizing RTILs, which are critically needed to solve many environmental problems, rely heavily on an improved physical understanding of the structural properties of the RTIL-H 2 O interface. We have been developing new "extremely" hydrophibiic ionic liquids for use in extractions and as biphasic media for reactions. Our goal is to probe the interfacial structure and dynamics of molecular species residing at the interface between these room temperature ionic liquids in contact with an aqueous solution. We use a number of spectroscopic techniques and electrochemical methods to unravel the structure of these interfaces.
- Kriech, M. A., Conboy, J. C., "Using the Intrinsic Chirality of a Molecule as a Label-Free Probe to Detect Molecular Adsorption to a Surface by Second Harmonic Generation", Applied Spectroscopy, 2005, 59, 746-753.
- Kriech, M. S., Conboy, J. C., "Imaging Chirality with Surface Second Harmonic Generation Microscopy", J. Am. Chem. Soc., 2005, 127, 2834-3835.
"Imagining Chiral Molecules on Surfaces", C&E News, 2005, 83, 32.
- Fitchett, B., Conboy, J. C., "Structure of the Room-Temperature Ionic Liquid/Si02 Interface Studied by Sum-Frequency Vibrational Spectroscopy", J. Phys. Chem. B, 2004, 108, 20255-20262.
- Liu, J., Conboy, J. C., "Direct Measurement of the Transbilayer Movement of Phospholipids by Sum-Frequency Vibrational Spectroscopy", J. Am. Chem. Soc. 2004 , 126 , 8376-8377.
- Liu, J., Conboy, J. C., "Phase Transition of a Single Lipid Bilayer Measured by Sum-Frequency Vibrational Spectroscopy", J. Am. Chem. Soc. 2004 , 126 , 8894-8895.
- Fitchett , B., Knepp , T., Conboy, J.C. ,"1-Alkyl-3-Methylimidazolium Bis ( perfluoroalkylsulfonyl ) imide Water-Immiscible Ionic Liquids: The Effect of Water on Electrochemical and Physical Properties", J. Electrochem. Soc. 2004 , 151 , E219-E225.
- Kriech , M. A., Conboy, J.C., "Counter-Propagating Second Harmonic Generation: a New Technique for the Investigation of Molecular Chirality at Interfaces", Opt. Soc. Am. B , 2004 , 21 , 1013-1022.
- Kriech , M. A., Conboy, J.C., "Measuring melittin binding to planar supported lipid bilayer by chiral second harmonic generation", Anal. Chim . Acta , 2003 , 496, (1-2), 143-153.
- Kriech , M. A., Conboy, J.C., "Label-Free Chiral Detection of Melittin Binding to a Membrane", J. Am. Chem. Soc., 2003 , 125, 1148-1149.