University of Hamburg, Biocenter Klein Flottbek, 22609 Hamburg, Germany.
Prog Lipid Res. 2010 Jul;49(3):262-88. doi: 10.1016/j.plipres.2010.02.001. Epub 2010 Feb 6.
The attachment of a sugar moiety to the 3-hydroxy group of a sterol drastically increases the size of the hydrophilic part of the lipid. It is obvious that the glycosylation of a considerable fraction of membrane-bound free sterols alters the biophysical properties of the membrane. However, the consequences of such changes in the proportions of free sterols and steryl glycosides on the biological functions of a membrane are still unclear. This is the main hurdle in understanding the biological functions of steryl glycosides on a molecular level. The recent cloning of sterol glycosyltransferase genes from plants, fungi and bacteria has enabled genetic approaches to analyze steryl glycoside functions. Down regulation of phytosteryl beta-glycoside biosynthesis in Arabidopsis thaliana causes several dysfunctions in seed development. Ergosteryl beta-glycoside depleted mutants of the yeast Pichia pastoris lose their ability to degrade their peroxisomes by an autophagic mechanism called micropexophagy. In the plant-pathogenic fungus Colletotrichum orbiculare the same defect impairs invasion of the cucumber host plants. Helicobacter pylori, a bacterium colonizing the human stomach, is unable to modulate the host's immune response when the cholesteryl alpha-glycoside biosynthesis of the bacterium is mutated. These mutants with manipulated steryl glycoside metabolism will inspire further studies with cell biological, biophysical and other methods that will provide us with a mechanistic understanding of steryl glycoside functions.
糖部分与甾醇的 3-羟基连接，极大地增加了脂质亲水部分的大小。显然，相当一部分膜结合游离甾醇的糖基化改变了膜的生物物理性质。然而，游离甾醇和甾基糖苷比例的这种变化对膜的生物学功能的影响仍不清楚。这是理解甾基糖苷在分子水平上的生物学功能的主要障碍。最近从植物、真菌和细菌中克隆甾醇糖基转移酶基因，使人们能够采用遗传方法来分析甾基糖苷的功能。拟南芥植物甾醇 β-糖苷生物合成的下调导致种子发育的几种功能障碍。毕赤酵母甾醇 β-糖苷耗尽突变体失去了通过称为微自噬的自噬机制降解过氧化物酶体的能力。在植物病原真菌胶孢炭疽菌中，同样的缺陷会损害其对黄瓜寄主植物的侵染。定植于人类胃中的细菌幽门螺杆菌，当其细菌胆甾醇 α-糖苷生物合成发生突变时，无法调节宿主的免疫反应。这些经过甾醇糖苷代谢操作的突变体将激发进一步的细胞生物学、生物物理学和其他方法的研究，为我们提供对甾醇糖苷功能的机制理解。
