title: Revisiting the bilayer structures of fluid phase phosphatidylglycerol lipids: Accounting for exchangeable hydrogens.
abstract: We recently published two papers detailing the structures of fluid phase phosphatidylglycerol (PG) lipid bilayers (Kučerka et al., 2012 J. Phys. Chem. B 116: 232-239; Pan et al., 2012 Biochim. Biophys. Acta Biomembr. 1818: 2135-2148), which were determined using the scattering density profile model. This hybrid experimental/computational technique utilizes molecular dynamics simulations to parse a lipid bilayer into components whose volume probabilities follow simple analytical functional forms. Given the appropriate scattering densities, these volume probabilities are then translated into neutron scattering length density (NSLD) and electron density (ED) profiles, which are used to jointly refine experimentally obtained small angle neutron and X-ray scattering data. However, accurate NSLD and ED profiles can only be obtained if the bilayer's chemical composition is known. Specifically, in the case of neutron scattering, the lipid's exchangeable hydrogens with aqueous D2O must be accounted for, as they can have a measureable effect on the resultant lipid bilayer structures. This was not done in our above-mentioned papers. Here we report on the molecular structures of PG lipid bilayers by appropriately taking into account the exchangeable hydrogens. Analysis indicates that the temperature-averaged PG lipid areas decrease by 1.5 to 3.8Å(2), depending on the lipid's acyl chain length and unsaturation, compared to PG areas when hydrogen exchange was not taken into account.
authors.affiliation: Department of Physics, University of South Florida, Tampa, FL 33620, USA. Electronic address: panj@usf.edu.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Pan
authors.affiliation: Department of Physics, Brock University, St. Catharines, ON L2S 3A1, Canada.
authors.forename: Drew
authors.initials: D
authors.lastname: Marquardt
authors.affiliation: Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Heberle
authors.affiliation: Department of Physical Chemistry of Drugs, Comenius University, 832 32 Bratislava, Slovakia; Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia.
authors.forename: Norbert
authors.initials: N
authors.lastname: Kučerka
authors.affiliation: Department of Physics, Brock University, St. Catharines, ON L2S 3A1, Canada; Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Joint Institute for Neutron Scattering, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA. Electronic address: katsarasj@ornl.gov.
authors.forename: John
authors.initials: J
authors.lastname: Katsaras
keywords: Hydrogen exchange; Lipid bilayer structure; MD simulations; PG lipid; SANS; SAXS