Department of Life Science and Institute of Biological Interfaces, Sogang University, Seoul, Korea.
Research Institute for Basic Science, Sogang University, Seoul, Korea.
PLoS Biol. 2022 Oct 3;20(10):e3001817. doi: 10.1371/journal.pbio.3001817. eCollection 2022 Oct.
Photoreceptors are light-sensitive proteins found in various organisms that respond to light and relay signals into the cells. Heliorhodopsin, a retinal-binding membrane protein, has been recently discovered, however its function remains unknown. Herein, we investigated the relationship between Actinobacteria bacterium IMCC26103 heliorhodopsin (AbHeR) and an adjacent glutamine synthetase (AbGS) in the same operon. We demonstrate that AbHeR binds to AbGS and regulates AbGS activity. More specifically, the dissociation constant (Kd) value of the binding between AbHeR and AbGS is 6.06 μM. Moreover, the absence of positively charged residues within the intracellular loop of AbHeR impacted Kd value as they serve as critical binding sites for AbGS. We also confirm that AbHeR up-regulates the biosynthetic enzyme activity of AbGS both in vitro and in vivo in the presence of light. GS is a key enzyme involved in nitrogen assimilation that catalyzes the conversion of glutamate and ammonia to glutamine. Hence, the interaction between AbHeR and AbGS may be critical for nitrogen assimilation in Actinobacteria bacterium IMCC26103 as it survives in low-nutrient environments. Overall, the findings of our study describe, for the first time, to the best of our knowledge, a novel function of heliorhodopsin as a regulatory rhodopsin with the capacity to bind and regulate enzyme activity required for nitrogen assimilation.
感光器是存在于各种生物体中的对光敏感的蛋白质，它们对光做出反应，并将信号传递到细胞中。最近发现了一种视紫红质结合膜蛋白——heliorhodopsin，但它的功能尚不清楚。在此，我们研究了同一操纵子中放线菌 IMCC26103 的 heliorhodopsin（AbHeR）和相邻的谷氨酰胺合成酶（AbGS）之间的关系。我们证明 AbHeR 与 AbGS 结合并调节 AbGS 活性。更具体地说，AbHeR 与 AbGS 结合的解离常数（Kd）值为 6.06 μM。此外，AbHeR 细胞内环中缺乏正电荷残基会影响 Kd 值，因为它们是 AbGS 的关键结合位点。我们还证实，在光照下，AbHeR 可在体外和体内均上调 AbGS 的生物合成酶活性。GS 是一种参与氮同化的关键酶，它催化谷氨酸和氨转化为谷氨酰胺。因此，AbHeR 和 AbGS 之间的相互作用可能对 IMCC26103 放线菌中的氮同化至关重要，因为它在营养物质匮乏的环境中生存。总的来说，我们的研究结果首次描述了 heliorhodopsin 的一个新功能，即作为一种调节视紫红质，具有结合和调节氮同化所需酶活性的能力。
