Rees, Douglas C. and Chang, Geoffrey and Spencer, Robert H. (2000) Crystallographic Analyses of Ion Channels: Lessons and Challenges. Journal of Biological Chemistry, 275 (2). pp. 713-716. ISSN 0021-9258 http://resolver.caltech.edu/CaltechAUTHORS:REEjbc00
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Membrane proteins fascinate at many levels, from their central functional roles in transport, energy transduction, and signal transduction processes to structural questions concerning how they fold and operate in the exotic environments of the membrane bilayer and the water-bilayer interface and to methodological issues associated with studying membrane proteins either in situ or extracted from the membrane. This interplay is beautifully exemplified by ion channels, a collection of integral membrane proteins that mediate the transmembrane passage of ions down their electrochemical potential gradient (for general reviews, see Refs. 1 and 2). Ion channels are key elements of signaling and sensing pathways, including nerve cell conduction, hormone response, and mechanosensation. The characteristic properties of ion channels reflect their conductance, ion selectivity, and gating. Ion channels are often specific for a particular type of ion (such as potassium or chloride) or a class of ions (such as anions) and are typically regulated by conformational switching of the protein structure between "open" and "closed" states. This conformational switching may be gated in response to changes in membrane potential, ligand binding, or application of mechanical forces. Detailed functional characterizations of channels and their gating mechanisms have been achieved, reflecting exquisite methodological advances such as patch clamp methods that can monitor the activities of individual channels (3). Until recently, corresponding information about the three-dimensional structures of channels was not available, reflecting difficulties in obtaining sufficient quantities of membrane proteins for crystallization trials. Happily, this situation has started to change with the structure determinations of the Streptomyces lividans K+ channel (KcsA (4)) and the Mycobacterium tuberculosis mechanosensitive channel (MscL (5)). A variety of reviews (6-12) have appeared recently that discuss functional implications of these channel structures. This review discusses these developments from a complementary perspective, by considering the implications of these structures from within the larger framework of membrane protein structure and function. Because of space restrictions, this review necessarily emphasizes membrane proteins that are composed primarily of alpha-helical bundles, such as KcsA and MscL, rather than beta-barrel proteins, such as porins, typically found in bacterial outer membranes.
|Additional Information:||Copyright © 2000 by the American Society for Biochemistry and Molecular Biology. The contributions of A. Lee and M. Barclay to the MscL structural work and discussions with R. Bass, K. Locher, D. Dougherty, and H. Lester on channels and membrane proteins are greatly appreciated. This minireview will be reprinted in the 2000 Minireview Compendium, which will be available in December, 2000.|
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|Deposited On:||20 Oct 2008 17:46|
|Last Modified:||26 Dec 2012 10:25|
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