title: Conformation of membrane-bound proteins revealed by vacuum-ultraviolet circular-dichroism and linear-dichroism spectroscopy.
abstract: Knowledge of the conformations of a water-soluble protein bound to a membrane is important for understanding the membrane-interaction mechanisms and the membrane-mediated functions of the protein. In this study we applied vacuum-ultraviolet circular-dichroism (VUVCD) and linear-dichroism (LD) spectroscopy to analyze the conformations of α-lactalbumin (LA), thioredoxin (Trx), and β-lactoglobulin (LG) bound to phosphatidylglycerol liposomes. The VUVCD analysis coupled with a neural-network analysis showed that these three proteins have characteristic helix-rich conformations involving several helical segments, of which two amphiphilic or hydrophobic segments take part in interactions with the liposome. The LD analysis predicted the average orientations of these helix segments on the liposome: two amphiphilic helices parallel to the liposome surface for LA, two hydrophobic helices perpendicular to the liposome surface for Trx, and a hydrophobic helix perpendicular to and an amphiphilic helix parallel to the liposome surface for LG. This sequence-level information about the secondary structures and orientations was used to formulate interaction models of the three proteins at the membrane surface. This study demonstrates the validity of a combination of VUVCD and LD spectroscopy in conformational analyses of membrane-binding proteins, which are difficult targets for X-ray crystallography and nuclear magnetic resonance spectroscopy.
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, 739-0046, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuo
authors.affiliation: Division of Molecular Science, Graduate School of Science and Technology, Gunma University, Kiryu, 376-8515, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Maki
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, 739-0046, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Namatame
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, 739-0046, Japan.|Department of Physical Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Taniguchi
authors.affiliation: Institute for Sustainable Sciences and Development, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Gekko
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D029968:Escherichia coli Proteins / Q000737:chemistry*; D007768:Lactalbumin / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D013879:Thioredoxins / Q000737:chemistry*; D014618:Vacuum
chemical_list: D029968:Escherichia coli Proteins; D007782:Lactoglobulins; D013879:Thioredoxins; D007768:Lactalbumin
keywords: liposome; membrane-binding sites; molecular orientation; protein-membrane interaction; secondary structures; synchrotron-radiation circular dichroism