title: Structural Basis for the Unusual QyRed-Shift and Enhanced Thermostability of the LH1 Complex from Thermochromatium tepidum.
abstract: While the majority of the core light-harvesting complexes (LH1) in purple photosynthetic bacteria exhibit a Qyabsorption band in the range of 870-890 nm, LH1 from the thermophilic bacterium Thermochromatium tepidum displays the Qyband at 915 nm with an enhanced thermostability. These properties are regulated by Ca2+ions. Substitution of the Ca2+with other divalent metal ions results in a complex with the Qyband blue-shifted to 880-890 nm and a reduced thermostability. Following the recent publication of the structure of the Ca-bound LH1-reaction center (RC) complex [Niwa, S., et al. (2014) Nature 508, 228], we have determined the crystal structures of the Sr- and Ba-substituted LH1-RC complexes with the LH1 Qyband at 888 nm. Sixteen Sr2+and Ba2+ions are identified in the LH1 complexes. Both Sr2+and Ba2+are located at the same positions, and these are clearly different from, though close to, the Ca2+-binding sites. Conformational rearrangement induced by the substitution is limited to the metal-binding sites. Unlike the Ca-LH1-RC complex, only the α-polypeptides are involved in the Sr and Ba coordinations in LH1. The difference in the thermostability between these complexes can be attributed to the different patterns of the network formed by metal binding. The Sr- and Ba-LH1-RC complexes form a single-ring network by the LH1 α-polypeptides only, in contrast to the double-ring network composed of both α- and β-polypeptides in the Ca-LH1-RC complex. On the basis of the structural information, a combined effect of hydrogen bonding, structural integrity, and charge distribution is considered to influence the spectral properties of the core antenna complex.
authors.affiliation: Faculty of Science, Ibaraki University , Mito 310-8512, Japan.
authors.forename: Long-Jiang
authors.initials: LJ
authors.lastname: Yu
authors.affiliation: Faculty of Science, Ibaraki University , Mito 310-8512, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kawakami
authors.affiliation: Department of Agrobioscience, Graduate School of Agriculture, Kobe University , Nada, Kobe 657-8501, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Kimura
authors.affiliation: Faculty of Science, Ibaraki University , Mito 310-8512, Japan.
authors.forename: Zheng-Yu
authors.initials: ZY
authors.lastname: Wang-Otomo
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001464:Barium / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002841:Chromatiaceae / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D008670:Metals / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D055550:Protein Stability; D013324:Strontium / Q000737:chemistry / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D008670:Metals; D001464:Barium; D002118:Calcium; D013324:Strontium