@article {2014|1717, title = {Lipid concentration and molar ratio boundaries for the use of isotropic bicelles.}, journal = {Langmuir}, volume = {30}, number = {21}, year = {2014}, month = {jun}, pages = {6162{\textendash}6170}, publisher = {Department of Chemistry, Universit{\'e} du Qu{\'e}bec {\`a} Montr{\'e}al and Centre Qu{\'e}b{\'e}cois sur les Mat{\'e}riaux Fonctionnels , P.O. Box 8888, Downtown Station, Montreal, Canada H3C 3P8.}, abstract = {Bicelles are model membranes generally made of long-chain dimyristoylphosphatidylcholine (DMPC) and short-chain dihexanoyl-PC (DHPC). They are extensively used in the study of membrane interactions and structure determination of membrane-associated peptides, since their composition and morphology mimic the widespread PC-rich natural eukaryotic membranes. At low DMPC/DHPC (q) molar ratios, fast-tumbling bicelles are formed in which the DMPC bilayer is stabilized by DHPC molecules in the high-curvature rim region. Experimental constraints imposed by techniques such as circular dichroism, dynamic light scattering, or microscopy may require the use of bicelles at high dilutions. Studies have shown that such conditions induce the formation of small aggregates and alter the lipid-to-detergent ratio of the bicelle assemblies. The objectives of this work were to determine the exact composition of those DMPC/DHPC isotropic bicelles and study the lipid miscibility. This was done using (31)P nuclear magnetic resonance (NMR) and exploring a wide range of lipid concentrations (2-400 mM) and q ratios (0.15-2). Our data demonstrate how dilution modifies the actual DMPC/DHPC molar ratio in the bicelles. Care must be taken for samples with a total lipid concentration <=250 mM and especially at q \~{} 1.5-2, since moderate dilutions could lead to the formation of large and slow-tumbling lipid structures that could hinder the use of solution NMR methods, circular dichroism or dynamic light scattering studies. Our results, supported by infrared spectroscopy and molecular dynamics simulations, also show that phospholipids in bicelles are largely segregated only when q > 1. Boundaries are presented within which control of the bicelles{\textquoteright} q ratio is possible. This work, thus, intends to guide the choice of q ratio and total phospholipid concentration when using isotropic bicelles.}, keywords = {chemistry, Circular Dichroism, Detergents, Dimyristoylphosphatidylcholine, Fourier Transform Infrared, Light, Lipid Bilayers, Magnetic Resonance Spectroscopy, Materials Testing, Micelles, Molecular Dynamics Simulation, Phospholipid Ethers, Phospholipids, Radiation, Scattering, Solutions, Spectroscopy, Temperature}, doi = {10.1021/la5004353}, author = {Beaugrand, Ma\"{\i}wenn and Arnold, Alexandre A. and J{\'e}r{\^o}me H{\'e}nin and Warschawski, Dror E. and Williamson, Philip T F. and Marcotte, Isabelle} } @article {2009|1830, title = {Replica exchange molecular dynamics simulations of coarse-grained proteins in implicit solvent.}, journal = {J. Phys. Chem. B}, volume = {113}, number = {1}, year = {2009}, month = {jan}, pages = {267{\textendash}274}, keywords = {Amino Acid Sequence, Computer Simulation, Magnetic Resonance Spectroscopy, Molecular Sequence Data, Peptides, Protein Folding, Protein Structure, Proteins, Secondary, Solvents, Temperature, Thermodynamics}, doi = {10.1021/jp805309e}, author = {Y Chebaro and Xiao Dong and Rozita Laghaei and Philippe Derreumaux and Normand Mousseau} } @article {1995|1941, title = {Solution structure of oligonucleotides covalently linked to a psoralen derivative.}, journal = {Nucleic Acids Res.}, volume = {23}, number = {5}, year = {1995}, month = {mar}, pages = {788{\textendash}795}, abstract = {

Psoralen (pso) was attached via its C-5 position to the 5\&$\#$39;-phosphate group of an oligodeoxynucleotide d(TAAGCCG) by a hexamethylene linker (m6). Complex formation between pso-m6-d(TAAGCCG) and the complementary strands d(CGGCTTA)[7-7mer] or d(CGGCTTAT)[7-8mer] was investigated by nuclear magnetic resonance in aqueous solution. Structural informations derived from DQF-COSY and NOESY maps, revealed that the mini double helix adopts a B-form conformation and that the deoxyriboses preferentially adopt a C2\&$\#$39;-endo conformation. The nOe connectivities observed between the protons of the bases or the sugars in each duplex, and the protons of the psoralen and the hexamethylene chain, led us to propose a model involving an equilibrium between two conformations due to different locations of the psoralen. Upon UV-irradiation, the psoralen moiety cross-linked the two DNA strands at the level of 5\&$\#$39;TpA3\&$\#$39; sequences. NMR studies of the single major photo-cross-linked duplex pso-m6-d(TAAGCCG) and d(CGGCTTA) were performed. The stereochemistry of the diadduct is indeed cis-syn at both cyclobutane rings. In addition, the effects of this diadduct on the helical structure are analyzed in detail.

}, keywords = {Base Sequence, chemistry, chemistry/radiation effects, Magnetic Resonance Spectroscopy, Models, Molecular, Molecular Sequence Data, Nucleic Acid Conformation, Oligodeoxyribonucleotides, Psoralens, Solutions}, author = {O. Bornet and Chantal Pr{\'e}vost and F. Vovelle and M. Chassignol and N. T. Thuong and G. Lancelot} }