β-carotene (BCR) is the most abundant carotenoid, a colorant, antioxidant, and provitamin A. The extreme hydrophobicity of this hydrocarbon requires special mechanisms for distribution in aqueous media, including water-soluble carotenoproteins. However, all known carotenoproteins prefer oxygenated carotenoids and bind BCR inefficiently. Here, we present the crystal structure of the BCR-binding protein (BBP) from gregarious male locusts, which is responsible for their vivid yellow body coloration, in complex with its natural ligand, BCR. BBP forms an antiparallel tubular homodimer with α/β-wrap folded monomers, each forming a hydrophobic 47 Å long, coaxial tunnel that opens outward and is occupied by one s-cisC6-C7, all-trans BCR molecule. In the BCR absence, BBP accepts a range of xanthophylls, with reduced efficiency depending on the position and number of oxygen atoms, but rejects lycopene. The structure captures a pigment complex with a Takeout 1 protein and inspires potential applications of BBP as a BCR solubilizer.

中文翻译：

---

可溶性蛋白质选择性结合 β-胡萝卜素的结构基础


β-胡萝卜素 （BCR） 是最丰富的类胡萝卜素、着色剂、抗氧化剂和维生素原 A。这种碳氢化合物的极强疏水性需要特殊的机制才能在水性介质中分布，包括水溶性胡萝卜素蛋白。然而，所有已知的胡萝卜素蛋白都喜欢含氧类胡萝卜素，并且结合 BCR 的效率低下。在这里，我们展示了来自群居雄蝗的 BCR 结合蛋白 （BBP） 的晶体结构，该蛋白负责其鲜艳的黄色体色，与其天然配体 BCR 形成复合物。BBP 与 α/β 包裹折叠单体形成一个反平行的管状同源二聚体，每个单体形成一个 47 Å 长的疏水性同轴隧道，该隧道向外打开，并被一个 s-cisC6-C7 全反式 BCR 分子占据。在没有 BCR 的情况下，BBP 接受一系列叶黄素，根据氧原子的位置和数量，效率降低，但拒绝番茄红素。该结构捕获了带有 Takeout 1 蛋白的色素复合物，并激发了 BBP 作为 BCR 增溶剂的潜在应用。