Cianci Michele, Rizkallah Pierre J, Olczak Andrzej, Raftery James, Chayen Naomi E, Zagalsky Peter F, Helliwell John R
Department of Chemistry, University of Manchester, Manchester M13 9PL, United Kingdom.
Proc Natl Acad Sci U S A. 2002 Jul 23;99(15):9795-800. doi: 10.1073/pnas.152088999. Epub 2002 Jul 15.
The binding of the carotenoid astaxanthin (AXT) in the protein multimacromolecular complex crustacyanin (CR) is responsible for the blue coloration of lobster shell. The structural basis of the bathochromic shift mechanism has long been elusive. A change in color occurs from the orange red of the unbound dilute AXT (lambda(max) 472 nm in hexane), the well-known color of cooked lobster, to slate blue in the protein-bound live lobster state (lambda(max) 632 nm in CR). Intriguingly, extracted CR becomes red on dehydration and on rehydration goes back to blue. Recently, the innovative use of softer x-rays and xenon derivatization yielded the three-dimensional structure of the A(1) apoprotein subunit of CR, confirming it as a member of the lipocalin superfamily. That work provided the molecular replacement search model for a crystal form of the beta-CR holo complex, that is an A(1) with A(3) subunit assembly including two bound AXT molecules. We have thereby determined the structure of the A(3) molecule de novo. Lobster has clearly evolved an intricate structural mechanism for the coloration of its shell using AXT and a bathochromic shift. Blue/purple AXT proteins are ubiquitous among invertebrate marine animals, particularly the Crustacea. The three-dimensional structure of beta-CR has identified the protein contacts and structural alterations needed for the AXT color regulation mechanism.
类胡萝卜素虾青素（AXT）与蛋白质多聚大分子复合物虾青蛋白（CR）的结合导致龙虾外壳呈现蓝色。红移机制的结构基础长期以来一直难以捉摸。颜色变化从未结合的稀AXT的橙红色（在己烷中λmax为472nm，即熟龙虾众所周知的颜色）转变为蛋白质结合的活龙虾状态下的石板蓝色（在CR中λmax为632nm）。有趣的是，提取的CR脱水后变红，再水化后又变回蓝色。最近，通过更软X射线和氙衍生化的创新应用，得到了CR的A(1)载脂蛋白亚基的三维结构，证实它是脂质运载蛋白超家族的一员。这项工作为β-CR全复合物的一种晶体形式提供了分子置换搜索模型，即一种包含两个结合的AXT分子的A(1)与A(3)亚基组装体。由此我们从头确定了A(3)分子的结构。龙虾显然已经进化出一种复杂的结构机制，利用AXT和红移来使外壳着色。蓝色/紫色AXT蛋白在无脊椎海洋动物中普遍存在，尤其是甲壳纲动物。β-CR的三维结构已经确定了AXT颜色调节机制所需的蛋白质接触和结构改变。
