Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Department of Medical Biochemistry, Kurume University School of Medicine, Kurume, Fukuoka, 830-0011, Japan.
Photosynth Res. 2019 Mar;139(1-3):163-171. doi: 10.1007/s11120-018-0573-1. Epub 2018 Sep 4.
Unique light-harvesting antennas in the green sulfur bacterium Chlorobaculum tepidum, called chlorosomes, consist of self-aggregates of bacteriochlorophyll (BChl) c. In the biosynthesis of BChl c, BciC demethoxycarbonylase removes the C13-methoxycarbonyl group to facilitate the self-aggregation of BChl c. We previously reported the in vitro BciC-enzymatic reactions and discussed the function of this enzyme in the biosynthesis of BChl c. This study aims to examine the substrate specificity of BciC in detail using several semi-synthetic (bacterio)chlorophyll derivatives. The results indicate that the substrate specificity of BciC is measurably affected by structural changes on the A/B rings including the bacteriochlorin π-systems. Moreover, BciC showed its activity on a Zn-chelated chlorophyll derivative. On the contrary, BciC recognized structural modifications on the D/E rings, including porphyrin pigments, which resulted in the significant decrease in the enzymatic activity. The utilization of BciC provides mild conditions that may be useful for the in vitro preparation of various chemically (un)stable chlorophyllous pigments.
在绿硫细菌中，被称为菌绿体的独特的光收集天线由细菌叶绿素 (BChl) c 的自聚集体组成。在 BChl c 的生物合成中，BciC 脱甲氧基羧基酶去除 C13-甲氧基羰基基团，以促进 BChl c 的自聚集。我们之前报道了体外 BciC 酶促反应，并讨论了该酶在 BChl c 生物合成中的功能。本研究旨在使用几种半合成（细菌）叶绿素衍生物详细研究 BciC 的底物特异性。结果表明，BciC 的底物特异性可通过 A/B 环上包括细菌叶绿素 π-系统的结构变化来衡量。此外，BciC 对 Zn 螯合叶绿素衍生物表现出活性。相反，BciC 识别 D/E 环上的结构修饰，包括卟啉色素，这导致酶活性显著降低。BciC 的利用提供了温和的条件，这可能对各种化学（不稳定）叶绿素色素的体外制备有用。
