de Sanctis Daniele, Dewilde Sylvia, Vonrhein Clemens, Pesce Alessandra, Moens Luc, Ascenzi Paolo, Hankeln Thomas, Burmester Thorsten, Ponassi Marco, Nardini Marco, Bolognesi Martino
Department of Physics, National Institute for the Physics of Matter (NFM), University of Genova, Genova I-16146, Italy.
J Biol Chem. 2005 Jul 22;280(29):27222-9. doi: 10.1074/jbc.M503814200. Epub 2005 May 24.
Hemoglobins at high concentration have been isolated long ago from some insect larvae living in hypoxic environments. Conversely, a monomeric hemoglobin has been discovered recently in the fruit fly Drosophila melanogaster as intracellular protein expressed both in larvae and in the adult fly. Such a finding indicates that the oxygen supply in insects may be more complex than previously thought, relying not only on O2 diffusion through the tubular tracheal system, but also on carrier-mediated transport and storage. We present here the crystal structure of recombinant D. melanogaster hemoglobin at 1.20 A resolution. Spectroscopic data show that the protein displays a hexacoordinated heme, whose axial ligands are the proximal and distal His residues. Such bis-His ligation of the heme has sizable effects on the protein local structure. Three protein matrix cavities, comparable in size but not in topological locations with those of sperm whale myoglobin, are spread through the protein matrix; one of these can host a xenon atom. Additionally, D. melanogaster hemoglobin binds one molecule of 3-(cyclohexylamino)propanesulfonic acid (CAPS) buffer at a surface pocket, next to the EF hinge. Despite the high resolution achieved, no sequence/structure features specifically supporting the heme hexa- to pentacoordination transition required for diatomic ligand binding could be recognized.
很久以前，人们就从一些生活在低氧环境中的昆虫幼虫体内分离出了高浓度的血红蛋白。相反，最近在果蝇中发现了一种单体血红蛋白，它作为一种细胞内蛋白质，在幼虫和成虫体内均有表达。这一发现表明，昆虫的氧气供应可能比之前认为的更为复杂，不仅依赖于氧气通过管状气管系统的扩散，还依赖于载体介导的运输和储存。我们在此展示了重组果蝇血红蛋白在1.20 Å分辨率下的晶体结构。光谱数据表明，该蛋白质呈现出六配位血红素，其轴向配体为近端和远端的组氨酸残基。血红素的这种双组氨酸配位对蛋白质的局部结构有显著影响。三个蛋白质基质腔散布在蛋白质基质中，其大小与抹香鲸肌红蛋白的基质腔相当，但拓扑位置不同；其中一个可以容纳一个氙原子。此外，果蝇血红蛋白在EF铰链旁边的一个表面口袋处结合一分子3-（环己基氨基）丙烷磺酸（CAPS）缓冲液。尽管分辨率很高，但未发现有特定的序列/结构特征能支持双原子配体结合所需的血红素从六配位到五配位的转变。
