Magnus K A, Lattman E E, Volbeda A, Hol W G
Department of Biophysics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Proteins. 1991;9(4):240-7. doi: 10.1002/prot.340090403.
Hemocyanins are copper-containing proteins that transport oxygen in a variety of invertebrates. Considerable evidence has accumulated that arthropodan hemocyanins are multimers of a fundamental hexameric unit. X-Ray crystallographic structure determination has revealed that the hemocyanin molecule from the spiny lobster Panulirus interruptus is a single hexamer having 32 point group symmetry. Using crystals of subunit II, one of 8 polypeptide types comprising the octahexameric hemocyanin of the horseshoe crab Limulus polyphemus, and the molecular replacement method for crystallographic phase determination we show that subunit II forms assemblies with the same hexameric quaternary structure as the whole Panulirus hemocyanin molecule. Observation of the same hexameric motif in two widely separated species provides strong additional evidence that this quaternary structural unit is a universal building block of arthropodan hemocyanins.
血蓝蛋白是一类含铜蛋白质，在多种无脊椎动物中负责运输氧气。大量证据表明，节肢动物的血蓝蛋白是由基本六聚体单元组成的多聚体。X射线晶体学结构测定显示，多刺龙虾（Panulirus interruptus）的血蓝蛋白分子是具有32点群对称性的单一六聚体。马蹄蟹（Limulus polyphemus）的八聚体血蓝蛋白由8种多肽类型组成，我们使用其中亚基II的晶体以及用于晶体学相位测定的分子置换方法，证明亚基II形成的聚集体具有与整个多刺龙虾血蓝蛋白分子相同的六聚体四级结构。在两个亲缘关系甚远的物种中观察到相同的六聚体基序，这进一步有力地证明了这种四级结构单元是节肢动物血蓝蛋白的通用构建模块。
