Photochemical Characterization of a New Heliorhodopsin from the Gram-Negative Eubacterium Bellilinea caldifistulae (BcHeR) and Comparison with Heliorhodopsin-48C12
Photochemical Characterization of a New Heliorhodopsin from the Gram-Negative Eubacterium Bellilinea caldifistulae (BcHeR) and Comparison with Heliorhodopsin-48C12
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DOI：
10.1021/acs.biochem.9b00257
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发表时间：
2019-07-02
期刊：
影响因子：
2.9
通讯作者：
Sudo, Yuki
中科院分区：
文献类型：
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作者：
Shibukawa, Atsushi;Kojima, Keiichi;Sudo, Yuki
许多微生物表达视紫红质，一种能够吸收阳光并利用这些能量进行重要生物功能（如ATP合成和趋光性）的色素膜蛋白。迄今为止发现的微生物紫红质被归类为1型紫红质。有趣的是，研究人员最近发现了一种新的微生物视紫红质家族，名为heliorhodopsin，它在系统发育上与1型视紫红质相距遥远。其中，只有革兰氏阳性真细菌的heliorhodopsin-48C12 （HeR-48C12）被光化学表征[Pushkarev， a ., et et . (2018) Nature 558, 595-599]。在这项研究中，我们以革兰氏阴性真细菌caldifistulae Bellilinea （BcHeR）的紫色日光紫红质为第二个例子进行了光化学表征，并确定了BcHeR和HeR-48C12之间哪些特性是保守的或不保守的。一系列的光化学测量揭示了它们之间的一些保守特性，包括在550 nm左右的可见吸收光谱，缺乏离子传输活性，以及在光循环过程中存在可能激活未知生物功能的二阶o型中间体。相比之下，HeR-48C12作为一种不保守的性质，虽然表现出视网膜的光适应状态，但BcHeR在黑暗和光适应条件下都表现出相同的视网膜构型。BcHeR和HeR-48C12光化学性质的比较是了解日光紫红质性质和功能作用的重要的第一步。
Many microorganisms express rhodopsins, pigmented membrane proteins capable of absorbing sunlight and harnessing that energy for important biological functions such as ATP synthesis and phototaxis. Microbial rhodopsins that have been discovered to date are categorized as type-1 rhodopsins. Interestingly, researchers have very recently unveiled a new microbial rhodopsin family named the heliorhodopsins, which are phylogenetically distant from type-1 rhodopsins. Among them, only heliorhodopsin-48C12 (HeR-48C12) from a Gram-positive eubacterium has been photochemically characterized [Pushkarev, A., et al. (2018) Nature 558, 595-599]. In this study, we photochemically characterize a purple-colored heliorhodopsin from Gram-negative eubacterium Bellilinea caldifistulae (BcHeR) as a second example and identify which properties are or are not conserved between BcHeR and HeR-48C12. A series of photochemical measurements revealed several conserved properties between them, including a visible absorption spectrum with a maximum at around 550 nm, the lack of ion-transport activity, and the existence of a second-order O-like intermediate during the photocycle that may activate an unidentified biological function. In contrast, as a property that is not conserved, although HeR-48C12 shows the light adaptation state of retinal, BcHeR showed the same retinal configuration under both dark and light-adapted conditions. These comparisons of photochemical properties between BcHeR and HeR-48C12 are an important first step toward understanding the nature and functional role of heliorhodopsins.