Green/red cyanobacteriochromes regulate complementary chromatic acclimation via a protochromic photocycle
Green/red cyanobacteriochromes regulate complementary chromatic acclimation via a protochromic photocycle
复制标题
DOI：
10.1073/pnas.1302909110
复制
发表时间：
2013-03-26
影响因子：
11.1
通讯作者：
Ikeuchi, Masahiko
中科院分区：
文献类型：
--
作者：
Hirose, Yuu;Rockwell, Nathan C.;Ikeuchi, Masahiko
蓝藻色素(CBCR)是光敏色素超家族中的蓝藻成员。与光致变色剂类似，CBCR通过共价结合的线性四吡咯(BLIN)发色团的光致异构化在两个光态之间转换。虽然光致变色剂是红色/远红光传感器，但CBCR在可见光和近紫外光(330-680 nm)范围内表现出不同的光周期。CBCR的两个亚家族通过“两个半胱氨酸的光循环”检测到近紫外光到蓝光(330-450 nm)，该光循环结合了碧林15Z/15E的光异构化和第二个碧林-半胱氨酸加合物的形成或消除。另一方面，调节光谱的绿色和红色区域之间的吸收的机制还没有被阐明。CCAS和RcaE是调节互补染色适应的CBCR亚家族的成员，在该亚家族中，蓝藻优化捕光触角，以响应绿色或红色环境光。CCAS已经被证明经历了绿色/红色光循环：在绿色吸收15Z状态(P-15Z(G))和红色吸收15E状态(P-15E(R))之间的可逆光转换。我们证明了来自Fremyella diplosiphon的RcaE经历了相同的光周期，并表现出光调节的激酶活性。在RcaE和CCAS中，毕林生色团被去质子化为P-15Z(G)而质子化为P-15E(R)。这种碧林质子化状态的变化受绿色/红色CBCR中保守的三个关键残基的调制。因此，我们将绿/红CBCR的光循环称为“原色光循环”，其中从绿吸收到红吸收的巨大变化不是由初始的Blin光异构化引起的，而是由随后的Blin质子化状态的变化引起的。
Cyanobacteriochromes (CBCRs) are cyanobacterial members of the phytochrome superfamily of photosensors. Like phytochromes, CBCRs convert between two photostates by photoisomerization of a covalently bound linear tetrapyrrole (bilin) chromophore. Although phytochromes are red/far-red sensors, CBCRs exhibit diverse photocycles spanning the visible spectrum and the near-UV (330-680 nm). Two CBCR subfamilies detect near-UV to blue light (330-450 nm) via a "two-Cys photocycle" that couples bilin 15Z/15E photoisomerization with formation or elimination of a second bilin-cysteine adduct. On the other hand, mechanisms for tuning the absorption between the green and red regions of the spectrum have not been elucidated as of yet. CcaS and RcaE are members of a CBCR subfamily that regulates complementary chromatic acclimation, in which cyanobacteria optimize light-harvesting antennae in response to green or red ambient light. CcaS has been shown to undergo a green/red photocycle: reversible photoconversion between a green-absorbing 15Z state (P-15Z(g)) and a red-absorbing 15E state (P-15E(r)). We demonstrate that RcaE from Fremyella diplosiphon undergoes the same photocycle and exhibits light-regulated kinase activity. In both RcaE and CcaS, the bilin chromophore is deprotonated as P-15Z(g) but protonated as P-15E(r). This change of bilin protonation state is modulated by three key residues that are conserved in green/red CBCRs. We therefore designate the photocycle of green/red CBCRs a "protochromic photocycle," in which the dramatic change from green to red absorption is not induced by initial bilin photoisomerization but by a subsequent change in bilin protonation state.