			Home About us Contact

Membrane Protein Structure (membrane + protein_structure)

Distribution by Scientific Domains

Life Sciences	50%
Chemistry	50%

Selected Abstracts

Lipid bilayers: an essential environment for the understanding of membrane proteins

MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007
Richard C. Page
Abstract Membrane protein structure and function is critically dependent on the surrounding environment. Consequently, utilizing a membrane mimetic that adequately models the native membrane environment is essential. A range of membrane mimetics are available but none generates a better model of native aqueous, interfacial, and hydrocarbon core environments than synthetic lipid bilayers. Transmembrane ,-helices are very stable in lipid bilayers because of the low water content and low dielectric environment within the bilayer hydrocarbon core that strengthens intrahelical hydrogen bonds and hinders structural rearrangements within the transmembrane helices. Recent evidence from solid-state NMR spectroscopy illustrates that transmembrane ,-helices, both in peptides and full-length proteins, appear to be highly uniform based on the observation of resonance patterns in PISEMA spectra. Here, we quantitate for the first time through simulations what we mean by highly uniform structures. Indeed, helices in transmembrane peptides appear to have backbone torsion angles that are uniform within ± 4° . While individual helices can be structurally stable due to intrahelical hydrogen bonds, interhelical interactions within helical bundles can be weak and nonspecific, resulting in multiple packing arrangements. Some helical bundles have the capacity through their amino acid composition for hydrogen bonding and electrostatic interactions to stabilize the interhelical conformations and solid-state NMR data is shown here for both of these situations. Solid-state NMR spectroscopy is unique among the techniques capable of determining three-dimensional structures of proteins in that it provides the ability to characterize structurally the membrane proteins at very high resolution in liquid crystalline lipid bilayers. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Novel free energy calculations to explore mechanisms and energetics of membrane protein structure and function

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2009
Wonpil Im
Abstract Understanding the delicate balance of forces governing helix or ,-hairpin interactions in transmembrane (TM) proteins is central to understanding membrane structure and function. These membrane constituent interactions play an essential role in determining the structure and function of membrane proteins, and protein interactions in membranes, and thus form the basis for many vital processes, including TM signaling, transport of ions and small molecules, energy transduction, and cell,cell recognition. "Why does a single-pass TM helix or ,-hairpin have specific orientations in membranes?" "What are the roles of hydrogen bonds, close packing, and helix-lipid or ,-hairpin-lipid interactions in helix or ,-hairpin associations in membranes?" "How do these interactions change the membrane structures?" "How do TM domains transmit signals across membranes?" These are important membrane biophysical questions that can be addressed by understanding the delicate balance of forces governing helix or ,-hairpin interactions with/in membranes. In this work, we summarize a series of helix/,-hairpin restraint potentials that we have developed, and illustrate their applications that begin to address the complicated energetics and molecular mechanisms of these interactions at the atomic level by calculating the potentials of mean force (PMFs) along reaction coordinates relevant to helix/,-hairpin motions in membranes and dissecting the total PMF into the contributions arising from physically important microscopic forces. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source]

Urea Unfolding of Opsin in Phospholipid Bicelles,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2009
Craig McKibbin
Opsin is the unstable apo-protein of the light-activated G protein-coupled receptor rhodopsin. We investigated the stability of bovine opsin, solubilized in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/detergent bicelles, against urea-induced unfolding. A single irreversible protein unfolding transition was observed from changes in intrinsic tryptophan fluorescence and far-UV circular dichroism. This unfolding transition correlated with loss of protein activity. Changes in tertiary structure, as indicated by fluorescence measurements, were concomitant with an approximate 50% reduction in ,-helical content of opsin, indicating that global unfolding had been induced by urea. The urea concentration at the midpoint of unfolding was dependent on the lipid/detergent environment, occurring at approximately 1.2 m urea in DMPC/1,2-dihexanoyl-sn-glycero-3-phosphocholine bicelles, while being significantly stabilized to approximately 3.5 m urea in DMPC/3-[(cholamidopropyl)dimethylammonio]-1-propanesulfonate bicelles. These findings demonstrate that interactions with the surrounding lipids and detergent are highly influential in the unfolding of membrane protein structure. The urea/bicelle system offers the possibility for a more detailed understanding of the structural changes that take place upon irreversible unfolding of opsin. [source]

Asymmetric amino acid compositions of transmembrane ,-strands

PROTEIN SCIENCE, Issue 8 2004
Aaron K. Chamberlain
Abstract In contrast to water-soluble proteins, membrane proteins reside in a heterogeneous environment, and their surfaces must interact with both polar and apolar membrane regions. As a consequence, the composition of membrane proteins' residues varies substantially between the membrane core and the interfacial regions. The amino acid compositions of helical membrane proteins are also known to be different on the cytoplasmic and extracellular sides of the membrane. Here we report that in the 16 transmembrane ,-barrel structures, the amino acid compositions of lipid-facing residues are different near the N and C termini of the individual strands. Polar amino acids are more prevalent near the C termini than near the N termini, and hydrophobic amino acids show the opposite trend. We suggest that this difference arises because it is easier for polar atoms to escape from the apolar regions of the bilayer at the C terminus of a ,-strand. This new characteristic of ,-barrel membrane proteins enhances our understanding of how a sequence encodes a membrane protein structure and should prove useful in identifying and predicting the structures of trans-membrane ,-barrels. [source]

Effects of ELF magnetic field on membrane protein structure of living HeLa cells studied by Fourier transform infrared spectroscopy

BIOELECTROMAGNETICS, Issue 7 2003
Toshitaka Ikehara
Abstract The effects of exposure to a 50 Hz magnetic field (maximum of 41.7 to 43.6 mT) on the membrane protein structures of living HeLa cells were studied using attenuated total reflection infrared spectroscopy. One min of such exposure shifted peak absorbance of the amide I band to a smaller wave number, reduced peak absorbance of the amide II band, and increased absorbance at around 1600 cm,1. These results suggest that exposure to the ELF magnetic field has reversible effects on the N,H inplane bending and C,N stretching vibrations of peptide linkages, and changes the secondary structures of ,-helix and ,-sheet in cell membrane proteins. Bioelectromagnetics 24:457,464, 2003. © 2003 Wiley-Liss, Inc. [source]