Graduate School of Integrated Science and Technology, Shizuoka University, Japan.
Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi, Japan.
FEBS J. 2020 Sep;287(18):4016-4031. doi: 10.1111/febs.15230. Epub 2020 Feb 15.
Bilin pigments play important roles for both light perception and harvesting in cyanobacteria by binding to cyanobacteriochromes (CBCRs) and phycobilisomes (PBS), respectively. Among various cyanobacteria, Acaryochloris marina MBIC 11017 (A. marina 11017) exceptionally uses chlorophyll d as the main photosynthetic pigment absorbing longer wavelength light than the canonical pigment, chlorophyll a, indicating existence of a system to sense longer wavelength light than others. On the other hand, A. marina 11017 has the PBS apparatus to harvest short-wavelength orange light, similar to most cyanobacteria. Thus, A. marina 11017 might sense longer wavelength light and harvest shorter wavelength light by using bilin pigments. Phycocyanobilin (PCB) is the main bilin pigment of both systems. Phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes PCB synthesis from biliverdin via the intermediate 18 ,18 -dihydrobiliverdin (18 ,18 -DHBV), resulting in the stepwise shortening of the absorbing wavelengths. In this study, we found that A. marina 11017 exceptionally encodes two PcyA homologs, AmPcyAc and AmPcyAp. AmPcyAc is encoded on the main chromosome with most photoreceptor genes, whereas AmPcyAp is encoded on a plasmid with PBS-related genes. High accumulation of 18 ,18 -DHBV for extended periods was observed during the reaction catalyzed by AmPcyAc, whereas 18 ,18 -DHBV was transiently accumulated for a short period during the reaction catalyzed by AmPcyAp. CBCRs could sense longer wavelength far-red light through 18 ,18 -DHBV incorporation, whereas PBS could only harvest orange light through PCB incorporation, suggesting functional diversification of PcyA as AmPcyAc and AmPcyAp to provide 18 ,18 -DHBV and PCB to the light perception and harvesting systems, respectively.
比尔林色素分别通过与藻胆体（PBS）和藻蓝蛋白（CBCR）结合，在蓝细菌中对光感知和光捕获起着重要作用。在各种蓝细菌中，海杆菌 MBIC 11017（A. marina 11017）异常地使用叶绿素 d 作为主要的光合色素，吸收比经典色素叶绿素 a 更长的波长的光，这表明存在一个感知比其他色素更长波长的光的系统。另一方面，A. marina 11017 具有 PBS 装置来捕获短波长的橙色光，这与大多数蓝细菌相似。因此，A. marina 11017 可能通过使用比尔林色素来感知更长波长的光和捕获更短波长的光。藻胆素（PCB）是两个系统的主要比尔林色素。藻蓝蛋白：铁氧还蛋白氧化还原酶（PcyA）催化 PCB 从胆绿素合成，通过中间产物 18,18 -二氢胆绿素（18,18 -DHBV），导致吸收波长逐渐缩短。在这项研究中，我们发现 A. marina 11017 异常编码两个 PcyA 同源物，AmPcyAc 和 AmPcyAp。AmPcyAc 编码在主染色体上，带有大多数光受体基因，而 AmPcyAp 编码在带有 PBS 相关基因的质粒上。在 AmPcyAc 催化的反应中，观察到 18,18 -DHBV 长时间高积累，而在 AmPcyAp 催化的反应中，18,18 -DHBV 短时间短暂积累。CBCR 可以通过 18,18 -DHBV 掺入来感知更长波长的远红光，而 PBS 只能通过 PCB 掺入来捕获橙色光，这表明 PcyA 的功能多样化，AmPcyAc 和 AmPcyAp 分别为光感知和光捕获系统提供 18,18 -DHBV 和 PCB。
