title: Ca(2+)-binding reduces conformational flexibility of RC-LH1 core complex from thermophile Thermochromatium tepidum.
abstract: The light-harvesting complex, LH1, of thermophile purple bacteria Thermochromatium tepidum consists of an array of α- and β-polypeptides which assemble the photoactive bacteriochlorophyll and closely interact with the membrane-lipids. In this study, we investigated the effect of calcium and manganese ions on the protein structure and thermostability of the reaction centre (RC)-LH1/lipid complex. The binding of Ca(2+), but not Mn(2+) is shown to shift the LH1 Q                         (                            y                         ) absorption maximum from ~889 to 915 nm and to significantly raise the thermostability of the RC-LH1 complex. The ATR-FTIR spectra indicate that interaction of Ca(2+) as monitored by the carboxylates' vibration of aspartate residues, but not Mn(2+) induces changes in the α-helix packing arrangement. The reduced rate of (1)H/(2)H exchange of proteins' amide protons shows that the accessibility to (2)H(2)O is significantly lowered in Ca(2+)-substituted RC-LH1/lipid complexes. In particular, exchange with the associated lipid molecules, is significantly retarded. These results suggest that the thermostability of the RC-LH1 complex is raised by the distinct interaction with calcium cations which reduces the RC-LH1/lipid dynamics, particularly, at the membrane-water interface.
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, 82152, Planegg-Martinsried, Germany.
authors.forename: Selma
authors.initials: S
authors.lastname: Jakob-Grun
authors.forename: Jara
authors.initials: J
authors.lastname: Radeck
authors.forename: Paula
authors.initials: P
authors.lastname: Braun
mesh_terms: D000595:Amino Acid Sequence; D001429:Bacteriochlorophylls / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002841:Chromatiaceae / Q000737:chemistry* / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D016415:Sequence Alignment; D013057:Spectrum Analysis; D013696:Temperature; D013997:Time Factors
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D008345:Manganese; D002118:Calcium