Bishop R E
Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, 6213 Medical Sciences Building, Toronto, Ont. M5S 1A8, Canada.
Biochim Biophys Acta. 2000 Oct 18;1482(1-2):73-83. doi: 10.1016/s0167-4838(00)00138-2.
The lipocalins were once regarded as a eukaryotic protein family, but new members have been recently discovered in bacteria. The first bacterial lipocalin (Blc) was identified in Escherichia coli as an outer membrane lipoprotein expressed under conditions of environmental stress. Blc is distinguished from most lipocalins by the absence of intramolecular disulfide bonds, but the presence of a membrane anchor is shared with two of its closest homologues, apolipoprotein D and lazarillo. Several common features of the membrane-anchored lipocalins suggest that each may play an important role in membrane biogenesis and repair. Additionally, Blc proteins are implicated in the dissemination of antibiotic resistance genes and in the activation of immunity. Recent genome sequencing efforts reveal the existence of at least 20 bacterial lipocalins. The lipocalins appear to have originated in Gram-negative bacteria and were probably transferred horizontally to eukaryotes from the endosymbiotic alpha-proteobacterial ancestor of the mitochondrion. The genome sequences also reveal that some bacterial lipocalins exhibit disulfide bonds and alternative modes of subcellular localization, which include targeting to the periplasmic space, the cytoplasmic membrane, and the cytosol. The relationships between bacterial lipocalin structure and function further illuminate the common biochemistry of bacterial and eukaryotic cells.
脂质运载蛋白曾被视为真核生物蛋白家族，但最近在细菌中发现了新成员。首个细菌脂质运载蛋白（Blc）是在大肠杆菌中作为一种在环境应激条件下表达的外膜脂蛋白被鉴定出来的。Blc与大多数脂质运载蛋白的区别在于缺乏分子内二硫键，但其与两个最接近的同源物——载脂蛋白D和拉扎里洛——一样都有膜锚定结构。膜锚定脂质运载蛋白的几个共同特征表明，每种蛋白可能在膜生物合成和修复中发挥重要作用。此外，Blc蛋白与抗生素抗性基因的传播以及免疫激活有关。最近的基因组测序工作揭示至少存在20种细菌脂质运载蛋白。脂质运载蛋白似乎起源于革兰氏阴性菌，可能是从线粒体的内共生α-变形菌祖先水平转移到真核生物中的。基因组序列还表明，一些细菌脂质运载蛋白具有二硫键和亚细胞定位的替代模式，包括定位于周质空间、细胞质膜和细胞质溶胶。细菌脂质运载蛋白结构与功能之间的关系进一步阐明了细菌和真核细胞的共同生物化学特性。
