Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
Photosynth Res. 2010 Jun;104(2-3):201-9. doi: 10.1007/s11120-009-9517-0. Epub 2010 Jan 22.
Candidatus Chloracidobacterium (Cab.) thermophilum is a recently discovered aerobic chlorophototroph belonging to the phylum Acidobacteria. From analyses of genomic sequence data, this organism was inferred to have type-1 homodimeric reaction centers, chlorosomes, and the bacteriochlorophyll (BChl) a-binding Fenna-Matthews-Olson protein (FMO). Here, we report the purification and characterization of Cab. thermophilum FMO. Absorption, fluorescence emission, and CD spectra of the FMO protein were measured at room temperature and at 77 K. The spectroscopic features of this FMO protein were different from those of the FMO protein of green sulfur bacteria (GSB) and suggested that exciton coupling of the BChls in the FMO protein is weaker than in FMO of GSB especially at room temperature. HPLC analysis of the pigments extracted from the FMO protein only revealed the presence of BChl a esterified with phytol. Despite the distinctive spectroscopic properties, the residues known to bind BChl a molecules in the FMO of GSB are well conserved in the primary structure of the Cab. thermophilum FMO protein. This suggests that the FMO of Cab. thermophilum probably also binds seven or possibly eight BChl a(P) molecules. The results imply that, without changing pigment composition or structure dramatically, the FMO protein has acquired properties that allow it to perform light harvesting efficiently under aerobic conditions.
嗜热脱氯杆菌（Cab. thermophilum）是一种最近发现的好氧叶绿素光合自养菌，属于酸杆菌门。根据基因组序列数据分析，该生物被推断具有 1 型同源二聚体反应中心、叶绿素体和细菌叶绿素（BChl）a 结合的 Fenna-Matthews-Olson 蛋白（FMO）。在这里，我们报告了嗜热脱氯杆菌 FMO 的纯化和表征。在室温下和 77 K 下测量了 FMO 蛋白的吸收、荧光发射和 CD 光谱。该 FMO 蛋白的光谱特征与绿硫细菌（GSB）的 FMO 蛋白不同，表明 FMO 蛋白中 BChls 的激子耦合比 GSB 的 FMO 蛋白弱，尤其是在室温下。从 FMO 蛋白中提取的色素的 HPLC 分析仅显示存在与植醇酯化的 BChl a。尽管光谱性质独特，但在 GSB 的 FMO 中与 BChl a 分子结合的残基在嗜热脱氯杆菌 FMO 蛋白的一级结构中很好地保守。这表明嗜热脱氯杆菌的 FMO 可能也结合了七个或可能八个 BChl a(P)分子。结果表明，在不显著改变色素组成或结构的情况下，FMO 蛋白已经获得了在有氧条件下高效进行光捕获的特性。
