期刊
PHOTOSYNTHESIS RESEARCH
卷 121, 期 1, 页码 3-12出版社
SPRINGER
DOI: 10.1007/s11120-014-9977-8
关键词
Bacteriochlorophyll-c; Bacteriochlorophyll-e; Methylation; Chlorosomes; Green sulfur bacteria; Ultra-fast HPLC
资金
- Japan Society for the Promotion of Science (JSPS) [22245030, 24550065, 24750169, 24107002]
- PRESTO (Precursory Research for Embryonic Science and Technology) fellowship from the Japan Science and Technology Agency (JST)
- Grants-in-Aid for Scientific Research [24107002, 24550065, 22245030, 24750169, 24550201] Funding Source: KAKEN
We recently constructed the mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum lacking BciD which was responsible for formation of a formyl group at the 7-position in bacteriochlorophyll(BChl)-e biosynthesis. This mutant exclusively gave BChl-c, but not BChl-e, as the chlorosome pigments (Harada et al. in PLoS One 8(4):e60026, 2013). By the mutation, the homolog and epimer composition of the pigment was drastically altered. The methylation at the 8(2)-position in the mutant cells proceeded to create BChl-c carrying large alkyl substituents at this position. Correspondingly, the content of BChls-c having the (S)-configuration at the chiral 3(1)-position remarkably increased and accounted for 80.6 % of the total BChl-c. Based on the alteration of the pigment composition in the mutant cells, a new BChl-c bearing the bulkiest, triple 8(2)-methylated neopentyl substituent at the 8-position ([N,E]BChl-c) was identified. The molecular structure of [N,E]BChl-c was fully determined by its NMR, mass, and circular dichroism spectra. The newly identified [N,E]BChl-c was epimerically pure at the chiral 3(1)-position and its stereochemistry was determined to be an (S)-configuration by modified Mosher's method. Further, the effects of the C8(2)-methylation on the optical absorption properties of monomeric BChls-c were investigated. The Soret but not Qy absorption bands shifted to longer wavelengths by the extra methylation (at most 1.4 nm). The C8(2)-methylation induced a slight but apparent effect on absorption properties of BChls-c in their monomeric states.
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