Membrane Organization And Dynamics

This volume brings together information on membrane organization and dynamics from a variety of spectroscopic, microscopic and simulation approaches, spanning a broad range of time scales. The implication of such dynamic information on membrane function in health and disease is a topic of contemporary interest. The chapters cover various aspects of membrane lipid and protein dynamics, explored using a battery of experimental and theoretical approaches. The synthesis of information and knowledge gained by utilizing multiple approaches will provide the reader with a comprehensive understanding of the underlying membrane dynamics and function, which will help to develop robust dynamic models for the understanding of membrane function in healthy and diseased states. In the last few years, crystal structures of an impressive number of membrane proteins have been reported, thanks to tremendous advances in membrane protein crystallization techniques. Some of these recently solved structures belong to the G protein-coupled receptor (GPCR) family, which are particularly difficult to crystallize due to their intrinsic flexibility. Nonetheless, these static structures do not provide the necessary information to understand the function of membrane proteins in the complex membrane milieu. This volume will address the dynamic nature of membrane proteins within the membrane and will provide the reader with an up-to date overview of the theory and practical approaches that can be used. This volume will be invaluable to researchers working in a wide range of scientific areas, from biochemistry and molecular biology to biophysics and protein science. Students of these fields will also find this volume very useful. This book will also be of great use to those who are interested in the dynamic nature of biological processes.

The first volume of the Handbook deals with the amazing world of biomembranes and lipid bilayers. Part A describes all aspects related to the morphology of these membranes, beginning with the complex architecture of biomembranes, continues with a description of the bizarre morphology of lipid bilayers and concludes with technological applications of these membranes. The first two chapters deal with biomembranes, providing an introduction to the membranes of eucaryotes and a description of the evolution of membranes. The following chapters are concerned with different aspects of lipids including the physical properties of model membranes composed of lipid-protein mixtures, lateralphase separation of lipids and proteins and measurement of lipid-protein bilayer diffusion. Other chapters deal with the flexibility of fluid bilayers, the closure of bilayers into vesicles which attain a large variety of different shapes, and applications of lipid vesicles and liposomes. Part B covers membrane adhesion, membrane fusion and the interaction of biomembranes withpolymer networks such as the cytoskeleton. The first two chapters of this part discuss the generic interactions of membranes from the conceptual point of view. The following two chapters summarize the experimental work on two different bilayer systems. The next chapter deals with the process ofcontact formation, focal bounding and macroscopic contacts between cells. The cytoskeleton within eucaryotic cells consists of a network of relatively stiff filaments of which three different types of filaments have been identified. As explained in the next chapter much has been recently learned aboutthe interaction of these filaments with the cell membrane. The final two chapters deal with membrane fusion.

Ls book is an account of what physical chemistry h . . to say about the structural, electrical and transport properties of biological membranes and their simplest model-the lipid bilayer. The accent throughout is on basic ideas. In contrast to the essentially descriptive ap proach characteristic of texts on membrane biochemistry, our underlying themes are the role of force and entropy in maintaining membrane organization, in determining the electric fields and ionic environment of membranes, and in regulating the passage of molecules and ions across membranes. Although experimental findings will always be the touch stone against which theory will be tried, no attempt is made to present an exhaustive survey of experimental data. On the other hand, there is discussion of the nature and limitations of the results obtainable by the major laboratory techniques. The treatment is at the level of an advanced undergraduate course or an introductory survey suitable for post graduate students carrying out research in biochemistry, biophysics, or physiology. The mathematical demands on the reader are trivial. The few forbidding equations appearing in Chapter 7 are soon whittled away to simple practical expressions. Although the current-voltage characteristics of nerves are traditionally the province of biophysics rather than physical chemistry, certain aspects relevant to the electrical activity of nerves are nevertheless included in this text, namely, mem brane and diffusion potentials and conductivity fluctuations. Where rival theories exist, conflicting convictions have been presented, but not necessarily accorded equal approbation. The author has a viewpoint.

The fluid-mosaic model of membrane structure formulated by Singer and Nicolson in the early 1970s has proven to be a durable concept in terms of the principles governing the organization of the constituent lipids and proteins. During the past 30 or so years a great deal of information has accumulated on the composition of various cell membranes and how this is related to the dif ferent functions that membranes perform. Nevertheless, the task of explaining particular functions at the molecular level has been hampered by lack of struc tural detail at the atomic level. The reason for this is primarily the difficulty of crystallizing membrane proteins which require strategies that differ from those used to crystallize soluble proteins. The unique exception is bacteriorhodopsin of the purple membrane of Halobacterium halobium which is interpolated into a membrane that is neither fluid nor in a mosaic configuration. To date only 50 or so membrane proteins have been characterised to atomic resolution by diffraction methods, in contrast to the vast data accumulated on soluble proteins. Another factor that has been difficult to explain is the reason why the lipid compliment of membranes is often extremely complex. Many hundreds of different molecular species of lipid can be identified in some membranes. Remarkably, the particular composition of each membrane appears to be main tained within relatively narrow limits and its identity distinguished from other morphologically-distinct membranes.

The study of membranes has become of high importance in the fields of biology, pharmaceutical chemistry and medicine, since much of what happens in a cell or in a virus involves biological membranes. The current book is an excellent introduction to the area, which explains how modern analytical methods can be applied to study biological membranes and membrane proteins and the bioprocesses they are involved to.

The interface between a living cell and the surrounding world plays a critical role in numerous complex biological processes. Sperm/egg fusion, virus/cell fusion, exocytosis, endocytosis, and ion permeation are a few examples of processes involving membranes. In recent years, powerful tools such as X-ray crystal lography, electron microscopy, nuclear magnetic resonance, and infra-red and Raman spectroscopy have been developed to characterize the structure and dy namics of biomembranes. Despite this progress, many of the factors responsible for the function of biomembranes are still not well understood. The membrane is a very complicated supramolecular liquid-crystalline structure that is largely composed of lipids, forming a bilayer, to which proteins and other biomolecules are anchored. Often, the lipid bilayer environment is pictured as a hydropho bic structureless slab providing a thermodynamic driving force to partition the amino acids of a membrane protein according to their solubility. However, much of the molecular complexity of the phospholipid bilayer environment is ignored in such a simplified view. It is likely that the atomic details of the polar head group region and the transition from the bulk water to the hydrophobic core of the membrane are important. An understanding of the factors responsible for the function of biomembranes thus requires a better characterization at the molec ular level of how proteins interact with lipid molecules, of how lipids affect protein structure and of how lipid molecules might regulate protein function.

The first volume of the Handbook deals with the amazing world of biomembranes and lipid bilayers. Part A describes all aspects related to the morphology of these membranes, beginning with the complex architecture of biomembranes, continues with a description of the bizarre morphology of lipid bilayers and concludes with technological applications of these membranes. The first two chapters deal with biomembranes, providing an introduction to the membranes of eucaryotes and a description of the evolution of membranes. The following chapters are concerned with different aspects of lipids including the physical properties of model membranes composed of lipid-protein mixtures, lateral phase separation of lipids and proteins and measurement of lipid-protein bilayer diffusion. Other chapters deal with the flexibility of fluid bilayers, the closure of bilayers into vesicles which attain a large variety of different shapes, and applications of lipid vesicles and liposomes. Part B covers membrane adhesion, membrane fusion and the interaction of biomembranes with polymer networks such as the cytoskeleton. The first two chapters of this part discuss the generic interactions of membranes from the conceptual point of view. The following two chapters summarize the experimental work on two different bilayer systems. The next chapter deals with the process of contact formation, focal bounding and macroscopic contacts between cells. The cytoskeleton within eucaryotic cells consists of a network of relatively stiff filaments of which three different types of filaments have been identified. As explained in the next chapter much has been recently learned about the interaction of these filaments with the cell membrane. The final two chapters deal with membrane fusion.