About this Research Topic
Our concepts of the structures and organizations of lipids and proteins within cellular membranes of eukaryotic cells are currently based on the Fluid-Mosaic Model of cell membrane structure (Singer SJ, Nicolson GL. Science 1972; 175:720-731). Although the model inferred certain properties of membrane proteins and their interactions with membrane lipids, detailed molecular structures and behaviors of eukaryotic membrane proteins have been traditionally studied in the absence of their lipid interactions. To determine the high-resolution structures of membrane proteins X-ray crystallography was first used by Diesenhofer et al. (Nature 1985; 318:618-624), but it has been only recently that lipid-protein interactions have been incorporated into integral membrane protein structural studies. Now at the beginning of the millennium new techniques aimed at overcoming this limitation, such as the use of membrane lipids and proteins in lipid vesicles, discoidal micelles and liquid crystal mesophases, have solved the problem of ascertaining membrane protein structure in its more native state interacting with membrane lipids. Thus from the earliest high-resolution crystallographic studies on bacteriorhodopsin (Deisenhofer, J. et al., Nature 1985; 318:618-624) to newer studies on eukaryotic membrane proteins undergoing structural changes during their catalytic cycles, opening and closing of ion channels, filtering of ionic passages, binding of agonists and inhibitors, and voltage-induced changes, among other events membrane proteins have slowly revealed their long-hidden structural secrets. Emerging from crystallographic structural studies our current understanding of integral membrane protein structure and function has evolved from single component solutions to much more complex multi-subunit, multi-component mixtures from secondary transporters to neurotransmitter receptors, and from ion channels to active transport pumps. The features and changes in integral membrane protein structures during human diseases have also opened up the possibility of developing large-scale screening approaches based on immobilized membrane proteins as well as the development of potential new therapeutic solutions to various diseases and clinical conditions. This research topic intends to offer a wide view of our current understanding of membrane protein structure and function that has emerged from the studies of crystal structures within the last two decades, including focused reviews on the latest research in the field of membrane protein crystallography and its applications to important biological and medical problems and new experimental and novel methodological approaches that take advantage of the latest technologies. Also, the evolution of membrane proteins and structures during the transition from prokaryote to eukaryote membranes as well as theoretical hypotheses on important problems in membrane protein structure and function will be encouraged. Finally, potential contributors will be able to emphasize the general principles leading to the retention of important protein structural characteristics and motifs that underlie the common functional roles of these fascinating molecular entities.
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