title: Probing the spatial organization of bacteriochlorophyll C by solid-state nuclear magnetic resonance.
abstract: Green sulfur bacteria, which live in extremely low-light environments, use chlorosomes to harvest light. A chlorosome is the most efficient, and arguably the simplest, light-harvesting antenna complex, which contains hundreds of thousands of densely packed bacteriochlorophylls (BChls). To harvest light efficiently, BChls in a chlorosome form supramolecular aggregates; thus, it is of great interest to determine the organization of the BChls in a chlorosome. In this study, we conducted a (13)C solid-state nuclear magnetic resonance and Mg K-edge X-ray absorption analysis of chlorosomes from wild-type Chlorobaculum tepidum. The X-ray absorption results indicated that the coordination number of the Mg in the chlorosome must be >4, providing evidence that electrostatic interactions formed between the Mg of a BChl and the carbonyl group or the hydroxyl group of the neighboring BChl molecule. According to the intermolecular distance constraints obtained on the basis of (13)C homonuclear dipolar correlation spectroscopy, we determined that the molecular assembly of BChls is dimer-based and that the hydrogen bonds among the BChls are less extensive than commonly presumed because of the twist in the orientation of the BChl dimers. This paper also reports the first (13)C homonuclear correlation spectrum acquired for carotenoids and lipids-which are minor, but crucial, components of chlorosomes-extracted from wild-type Cba. tepidum.
authors.affiliation: Department of Chemistry and ‡Instrumentation Center, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Shih-Chi
authors.initials: SC
authors.lastname: Luo
authors.forename: Yadana
authors.initials: Y
authors.lastname: Khin
authors.forename: Shing-Jong
authors.initials: SJ
authors.lastname: Huang
authors.forename: Yanshen
authors.initials: Y
authors.lastname: Yang
authors.forename: Tsai-Yi
authors.initials: TY
authors.lastname: Hou
authors.forename: Yuan-Chung
authors.initials: YC
authors.lastname: Cheng
authors.forename: Hao Ming
authors.initials: HM
authors.lastname: Chen
authors.forename: Yi-Ying
authors.initials: YY
authors.lastname: Chin
authors.forename: Chien-Te
authors.initials: CT
authors.lastname: Chen
authors.forename: Hong-Ji
authors.initials: HJ
authors.lastname: Lin
authors.forename: Joseph Kuo-Hsiang
authors.initials: JK
authors.lastname: Tang
authors.forename: Jerry Chun Chung
authors.initials: JC
authors.lastname: Chan
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls / Q000737:chemistry*; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D002338:Carotenoids / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D011487:Protein Conformation; D066244:Proton Magnetic Resonance Spectroscopy
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D008055:Lipids; D002338:Carotenoids; C002084:bacteriochlorophyll c