Isolation and characterization of a new bacteriochlorophyll-c bearing a neopentyl substituent at the C8-position from the bciD-deletion mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum
Isolation and characterization of a new bacteriochlorophyll-c bearing a neopentyl substituent at the C8-position from the bciD-deletion mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum
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从棕色绿色硫细菌 Chlorobaculum limnaeum 的 bciD 缺失突变体中分离和表征 C8 位带有新戊基取代基的新细菌叶绿素-c
DOI：
10.1007/s11120-014-9977-8
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
H. Tamiaki
中科院分区：
文献类型：
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作者：
T. Mizoguchi;J. Harada;Y. Tsukatani;H. Tamiaki
我们最近构建了棕色绿色硫细菌Chlorobaculum limnaeum的BciD缺失突变体，该突变体负责细菌叶绿素（BChl）-e生物合成中7位甲酰基的形成。该突变体仅产生BChl-c而不是BChl-e作为叶绿体色素（Harada等人，PLoS One 8（4）：e60026，2013）。通过突变，色素的同系物和差向异构体组成发生了急剧变化。突变细胞中82位的甲基化继续产生在该位置携带大的烷基取代基的BChl-c。相应地，在手性31位具有（S）-构型的BChls含量显著增加，占总BChl-c的80.6%。基于突变体细胞中色素组成的改变，鉴定了一个新的BChl-c，其在8位具有最大的三个82-甲基化新戊基取代基（[N，E]BChl-c）。[N，E] BChl-c的分子结构由其NMR、质谱和圆二色谱完全确定。新鉴定的[N，E] BChl-c在手性31位为差向异构纯，其立体化学经改进的Mosher方法确定为（S）-构型。进一步研究了C82-甲基化对单体BChls-c光吸收性质的影响。Soret而不是Qy吸收带通过额外的甲基化（至多1.4nm）向更长的波长移动。C82-甲基化对BChls-cin单体状态下的吸收特性有轻微但明显的影响。
We recently constructed the mutant of the brown-colored green sulfur bacteriumChlorobaculum limnaeumlacking BciD which was responsible for formation of a formyl group at the 7-position in bacteriochlorophyll(BChl)-ebiosynthesis. 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 82-position in the mutant cells proceeded to create BChl-ccarrying large alkyl substituents at this position. Correspondingly, the content of BChls-chaving the (S)-configuration at the chiral 31-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-cbearing the bulkiest, triple 82-methylated neopentyl substituent at the 8-position ([N,E]BChl-c) was identified. The molecular structure of [N,E]BChl-cwas fully determined by its NMR, mass, and circular dichroism spectra. The newly identified [N,E]BChl-cwas epimerically pure at the chiral 31-position and its stereochemistry was determined to be an (S)-configuration by modified Mosher’s method. Further, the effects of the C82-methylation on the optical absorption properties of monomeric BChls-cwere investigated. The Soret but not Qy absorption bands shifted to longer wavelengths by the extra methylation (at most 1.4 nm). The C82-methylation induced a slight but apparent effect on absorption properties of BChls-cin their monomeric states.