Keen J N, Caceres I, Eliopoulos E E, Zagalsky P F, Findlay J B
Department of Biochemistry and Molecular Biology, University of Leeds, England.
Eur J Biochem. 1991 Nov 15;202(1):31-40. doi: 10.1111/j.1432-1033.1991.tb16340.x.
The complete sequence has been determined for the C1 subunit of crustacyanin, an astaxanthin-binding protein from the carapace of the lobster Homarus gammarus (L.). The polypeptide, 181 residues long, is similar (38% identity) to the other main subunit, A2 and to plasma retinol-binding protein. The tertiary structure of the C1 subunit has been modelled on that derived for the A2 subunit from the coordinates of retinol-binding protein. Residues lining the putative binding cavities and at the putative carotenoid binding sites of the two subunits are highly conserved. The carotenoid environments are characterized by a preponderance of aromatic and polar residues and the absence of charged side-chains. A tentative model for the dimer, beta-crustacyanin, formed between the two subunits with their associated carotenoid ligands, is discussed. The model is based on the crystal structure of the dimer of bilin-binding protein, a member of the same superfamily. This structure has enabled us to examine mechanisms for the bathochromic spectral shift of the protein-bound carotenoid and to identify likely contact regions between dimers in octameric alpha-crustacyanin.
已经确定了龙虾（螯龙虾）外壳中虾青素结合蛋白——虾青蛋白C1亚基的完整序列。该多肽由181个残基组成，与另一个主要亚基A2以及血浆视黄醇结合蛋白相似（同一性为38%）。C1亚基的三级结构已根据视黄醇结合蛋白的坐标为A2亚基推导的结构进行建模。两个亚基假定的结合腔内壁和假定的类胡萝卜素结合位点处的残基高度保守。类胡萝卜素环境的特征是芳香族和极性残基占优势且没有带电荷的侧链。讨论了由两个亚基及其相关类胡萝卜素配体形成的二聚体β-虾青蛋白的初步模型。该模型基于同一超家族成员——胆红素结合蛋白二聚体的晶体结构。这种结构使我们能够研究蛋白质结合类胡萝卜素的红移光谱机制，并确定八聚体α-虾青蛋白中二聚体之间可能的接触区域。
