Structural and Functional Modularity of the Orange Carotenoid Protein: Distinct Roles for the N- and C-Terminal Domains in Cyanobacterial Photoprotection
Structural and Functional Modularity of the Orange Carotenoid Protein: Distinct Roles for the N- and C-Terminal Domains in Cyanobacterial Photoprotection
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DOI：
10.1105/tpc.113.118588
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发表时间：
2014-01-01
期刊：
影响因子：
11.6
通讯作者：
Kerfeld, Cheryl A.
中科院分区：
文献类型：
--
作者：
Leverenz, Ryan L.;Jallet, Denis;Kerfeld, Cheryl A.
橙类胡萝卜素蛋白（OCP）在蓝藻中作为光强度传感器和藻胆酶体（PB）相关光保护的效应体。在结构上，OCP由一个类胡萝卜素发色团跨越的两个不同的区域组成。在功能上，为了响应强光，OCP从暗稳定的橙色形式OCPO转换为活跃的红色形式OCPR。OCP的c端结构域参与了对光强的动态响应，并通过与荧光恢复蛋白的相互作用在关闭OCP的光保护响应中发挥作用。n端结构域的功能，这是唯一发现在蓝藻，是不清楚的。为了研究其功能，我们利用天然OCP的有限蛋白水解在体外分离出n端结构域。n端结构域保留类胡萝卜素发色团；该红色类胡萝卜素蛋白（RCP）具有与活性全长OCPR相当的组成PB荧光猝灭活性。RCP与OCPR的光谱特性比较表明，在OCPR形式下，c端结构域内关键的蛋白质发色团相互作用减弱。这些结果表明，c端结构域可以动态调节与n端结构域结合的类胡萝卜素的光保护活性。
The orange carotenoid protein (OCP) serves as a sensor of light intensity and an effector of phycobilisome (PB)-associated photoprotection in cyanobacteria. Structurally, the OCP is composed of two distinct domains spanned by a single carotenoid chromophore. Functionally, in response to high light, the OCP converts from a dark-stable orange form, OCPO, to an active red form, OCPR. The C-terminal domain of the OCP has been implicated in the dynamic response to light intensity and plays a role in switching off the OCP's photoprotective response through its interaction with the fluorescence recovery protein. The function of the N-terminal domain, which is uniquely found in cyanobacteria, is unclear. To investigate its function, we isolated the N-terminal domain in vitro using limited proteolysis of native OCP. The N-terminal domain retains the carotenoid chromophore; this red carotenoid protein (RCP) has constitutive PB fluorescence quenching activity comparable in magnitude to that of active, full-length OCPR. A comparison of the spectroscopic properties of the RCP with OCPR indicates that critical proteinchromophore interactions within the C-terminal domain are weakened in the OCPR form. These results suggest that the C-terminal domain dynamically regulates the photoprotective activity of an otherwise constitutively active carotenoid binding N-terminal domain.