Membrane Structural Biology
Bioinformatics, Biomaterials, Controlled Release, High-Throughput Crystallography, Databases, Drug Delivery, Lipidomics, Membrane Protein Structure and Function, Rational Design, Robotics, X-Ray Methods
The elucidation of the structure and function of cellular membranes remains today one of the grand challenges in structural biology. While much attention has been paid to the protein component of membranes in the past, the lipid component is increasingly being recognized as an active player in the life of the membrane. The cross-disciplinary research being conducted in my group is concerned with both membrane components. The reductionist approach is adopted which involves establishing behaviors of components in isolation first and then building up a view of the intact biological membrane in a series of reconstitution studies where lipids and proteins acting in concert are studied. What makes lipids so interesting as biomaterials is that they exhibit liquid crystalline properties. Much of our work focuses on this important property. A variety of biochemical, biophysical, synthetic and analytical techniques are used in this research program and a sizable effort is devoted to making state-of-the-art measurements at x-ray synchrotron facilities worldwide. A summary of our research interests in the area of membrane structure and function follows.
Membrane Protein Structure A major breakthrough in determining the structure and function of membrane proteins occurred recently with the advent of a technique for growing crystals of membrane proteins from lipid cubic mesophases. We are using our understanding of lipid phase science to decipher the mechanism of crystal growth and are extending the method to several important membrane proteins. A major effort is underway to miniaturize and to robotize the crystallization process. This is part of a high-throughput structural proteomics initiative aimed at determining the structure and function of the proteins in Mycobacterium tuberculosis, the organism responsible for tuberculosis.
Membrane Fusion Much of intra- and inter-cellular communication is mediated by a process that requires membranes to fuse. Our objective here is to understand the mechanism whereby lipids and proteins function in this ubiquitous and vital process. To this end, a method referred to as time-resolved x-ray diffraction has been developed that enables the direct and quantitative measurement of the dynamics of phase transitions believed to occur during membrane fusion. Mechanistic insights are provided by the ability to detect transition intermediates and by impulse-response studies. These investigations seek to augment our appreciation of the physiological role of membrane lipids and proteins in fusion and related cellular events.
Rational Design Principles / Environmental Chemistry The monoacylglycerols are important intermediates in fat metabolism. They display a remarkable variety of liquid crystal phases when dispersed in water. We wish to establish the rules governing liquid crystal phase propensity and mesoscopic topology as determined by molecular structure and are working with a series of synthetic monoacylglycerols for this purpose. The principles that emerge from this work will help decipher the membrane lipid dispersity enigma and will be used in rational design of biocompatible materials for encapsulation, controlled release, and uptake and drug delivery. This area of research involves organic synthesis, mesophase structure/materials characterization using x-ray diffraction, calorimetry and curvature elastic energy calculations, and transport studies with drugs, proteins, nucleic acids on the one hand, and environmentally sensitive chemicals (pollutants) on the other.
Cholesterol, Polyunsaturated Fatty Acids Cholesterol and polyunsaturated fatty acids-containing lipids have profound effects on the phase properties and thus, the function, of natural membranes. Domain, also known as raft, formation within the membrane is triggered by high cholesterol in a way that is sensitive to the polyunsaturated fatty acid-containing lipid profile of the membrane. Phase relations and lipid dynamics of these model membrane systems are being investigated using x-ray diffraction and nuclear magnetic resonance in collaboration with S. Wassall at IUPUI, Indianapolis, IN. The goal is to understand how domain formation and membrane function are regulated in vivo.
Radiation Damage The call for brighter synchrotron x-radiation sources for use in structural biology research is barely audible as we embark on the new millennium. Our brightest sources are already creating havoc when used at design specifications because of damage. The problem of radiation damage is particularly severe in studies involving kinetics and mechanism where cryotechniques are not always viable. Accordingly, we need to understand the very nature of radiation damage and to devise means for minimizing it. This is the thrust of the current project as applied to lipid membranes and mesophases, and to crystals of macromolecules. Thus far, we have reported on two very different types of radiation damage. One involves a dramatic phase transformation and the other a disordering of lamellar stacking. How beam energy, accumulated dose, dose-rate, scavengers, etc., affect damage is under investigation. The work highlights the nature of the damage process and the need for additional studies with a view to making most efficient use of an important resource, synchrotron radiation. We have demonstrated that damage is free radical mediated. This finding is of additional interest as it may have implications for age-related changes in membrane properties. Radiation damage as applied to crystals of macromolecules is being done in collaboration with Drs. R. Ravelli and S. McSweeney at the ESRF/EMBL (Grenoble, France) and with Dr. E. Garman (University of Oxford, England).
Bio- and Chemi-informatics Lipidomics is a fledgling discipline where lipids, also known as fats, take center stage. Of particular interest within the area are the distribution of lipids in biological systems in health and disease, and the relationship that exists between lipid structure and function. The Lipid Data Bank (LDB,www.caffreylabs.ul.ie) is a suite of web-based relational databases containing quantitative information critical to understanding the structure-function relationship and lipid distribution profiles. A long-term objective of lipidomics is the exploitation of this understanding for the purpose of rational design and control. The LDB is a collection of Web-based relational databases serving a diverse community with an interest in lipids and membranes. It includes i) LIPIDAT, a database of lipid phases, phase transition temperatures and enthalpy change values, ii) LIPIDAG, a database of phase diagrams dealing with lipid miscibility, and iii) LMSD, where lipid molecular structures are housed.
Martin Caffrey received a B. Agr. Sc from University College, Dublin, in 1972. He then moved to Cornell University where he received an M.S. in food science in 1976 and a Ph.D. in biochemistry in 1982. He remained on as an independent investigator at Cornell University until 1988 when he joined the Department of Chemistry faculty at The Ohio State University. In the fall of 2003, he assumed the position of Professor of Membrane Structural Biology at The University of Limerick supported in part by an Investigatorship from Science Foundation Ireland. His objectives include establishing a Centre For Membrane Structural Biology at the University of Limerick. He continues to hold an adjunct professor position in the Chemistry Department at The Ohio State University.
Members of the research group including students will have an opportunity to work for several weeks to months at a time at The Ohio State University (Columbus, OH, USA), and at x-ray synchrotron facilities worldwide. Most of the group's x-ray data collection is done currently at the Advanced Photon Source, Argonne National Laboratory (Chicago, USA), the Cornell High Energy Synchrotron Source (Ithaca, NY, USA), the National Synchrotron Light Source (Brookhaven, NY, USA), and the European Synchrotron Radiation Facility (Grenoble, France).
Please contact Professor Caffrey directly by email (firstname.lastname@example.org
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