Structural and spectroscopic characterization of HCP2
Structural and spectroscopic characterization of HCP2
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DOI：
10.1016/j.bbabio.2019.03.004
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发表时间：
2019-05-01
影响因子：
4.3
通讯作者：
Kerfeld, Cheryl A.
中科院分区：
文献类型：
--
作者：
Dominguez-Martin, Maria Agustina;Polivka, Tomas;Kerfeld, Cheryl A.
螺旋类胡萝卜素蛋白（HCPs）是一大类新发现的类胡萝卜素结合蛋白，存在于生态生理多样化的蓝藻中。它们可能在成为模块化橙色类胡萝卜素蛋白（OCP）的效应域（猝灭）域之前进化。离散HCP家族的数量——至少有9个——表明它们参与多种不同的功能。在这里，我们报道了自然界中发现的最广泛的HCPs之一HCP2的1.7埃晶体结构，来自色适应蓝藻Tolypothrix sp. PCC 7601。通过从天然来源纯化HCP2，我们能够鉴定其天然结合的类胡萝卜素，这是唯一的角黄素。溶液中，HCP2为单体，吸光度最大值为530 nm。然而，HCP2晶体在548 nm处具有最大吸光度，这是由于类胡萝卜素的β 1环在不对称单元中的两个分子中堆叠。我们的研究结果表明，HCPs为研究类胡萝卜素-蛋白质相互作用及其光谱含义提供了一个有价值的系统，并有助于理解这一庞大的、新发现的色素蛋白家族的功能作用，这一家族迄今仍是一个谜。
The Helical Carotenoid Proteins (HCPs) are a large group of newly identified carotenoid-binding proteins found in ecophysiologically diverse cyanobacteria. They likely evolved before becoming the effector (quenching) domain of the modular Orange Carotenoid Protein (OCP). The number of discrete HCP families-at least nine-suggests they are involved in multiple distinct functions. Here we report the 1.7 angstrom crystal structure of HCP2, one of the most widespread HCPs found in nature, from the chromatically acclimating cyanobacterium Tolypothrix sp. PCC 7601. By purifying HCP2 from the native source we are able to identify its natively-bound carotenoid, which is exclusively canthaxanthin. In solution, HCP2 is a monomer with an absorbance maximum of 530 nm. However, the HCP2 crystals have a maximum absorbance at 548 nm, which is accounted by the stacking of the beta 1 rings of the carotenoid in the two molecules in the asymmetric unit. Our results demonstrate how HCPs provide a valuable system to study carotenoid-protein interactions and their spectroscopic implications, and contribute to efforts to understand the functional roles of this large, newly discovered family of pigment proteins, which to-date remain enigmatic.