Rodenburg Kees W, Van der Horst Dick J
Department of Biochemical Physiology, Faculty of Biology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Biochim Biophys Acta. 2005 Sep 5;1736(1):10-29. doi: 10.1016/j.bbalip.2005.07.002.
In all animals, lipoproteins are used to transport lipids through the aqueous circulation. Lipids are delivered to mammalian cells by two different mechanisms: via endocytic uptake of the complete lipoprotein particle mediated by members of the low density lipoprotein (LDL) receptor (LDLR) family, or by selective delivery of lipoprotein-carried lipids at the cell surface, such as lipid uptake following the action of a lipoprotein lipase. Although many structural elements of the lipid transport system of insects are similar to those of mammals, insect lipoprotein-mediated lipid transport was thought to apply only to the latter concept, since the single lipoprotein acts as a reusable lipid shuttle. However, the recent identification of lipoprotein receptors of the LDLR family in insects suggests that lipid transport in these animals may also adopt the first concept. Yet, the endocytic properties of the insect LDLR homologue appear to deviate from those of the mammalian LDLR family members, resulting in the recycling of endocytosed lipoprotein in a transferrin-like manner. This indicates that a hitherto unknown as well as unexpected function can be added to the plethora of functions of LDLR family members. Analysis of the molecular mechanism of the ligand-recycling function of the insect receptor provides also new insight into the possible functioning of the mammalian family members. In the last several years, mammalian and insect lipoprotein-mediated lipid transport systems have been reviewed separately with respect to functioning and lipid delivery. This review, in which new and important developments in the insect field with respect to our understanding of lipid delivery are discussed with a particular focus on the involvement of the LDLR homologue, aims at comparing the two systems, also from an evolutionary biological perspective, and proposes that the two systems are more similar than assumed previously.
在所有动物中，脂蛋白用于通过血液循环输送脂质。脂质通过两种不同机制输送到哺乳动物细胞：通过低密度脂蛋白（LDL）受体（LDLR）家族成员介导的完整脂蛋白颗粒的内吞摄取，或通过脂蛋白携带的脂质在细胞表面的选择性输送，例如脂蛋白脂肪酶作用后的脂质摄取。尽管昆虫脂质运输系统的许多结构元件与哺乳动物的相似，但昆虫脂蛋白介导的脂质运输被认为仅适用于后一种概念，因为单一脂蛋白充当可重复使用的脂质穿梭体。然而，最近在昆虫中鉴定出LDLR家族的脂蛋白受体，这表明这些动物中的脂质运输也可能采用第一种概念。然而，昆虫LDLR同源物的内吞特性似乎与哺乳动物LDLR家族成员的不同，导致内吞的脂蛋白以类似转铁蛋白的方式循环利用。这表明可以在LDLR家族成员的众多功能中添加一种迄今未知且意想不到的功能。对昆虫受体配体循环功能分子机制的分析也为哺乳动物家族成员的可能功能提供了新的见解。在过去几年中，已分别就功能和脂质输送对哺乳动物和昆虫脂蛋白介导的脂质运输系统进行了综述。本综述讨论了昆虫领域在脂质输送理解方面的新的重要进展，特别关注LDLR同源物的参与，旨在从进化生物学角度比较这两种系统，并提出这两种系统比以前认为的更相似。
