Department of Biochemistry, University of Nebraska-Lincoln, 1901 Vine St, Lincoln, NE, 68588, USA.
Photosynth Res. 2018 Dec;138(3):345-360. doi: 10.1007/s11120-018-0545-5. Epub 2018 Jun 30.
Photosynthetic membranes provide much of the usable energy for life on earth. To produce photosynthetic membrane lipids, multiple transport steps are required, including fatty acid export from the chloroplast stroma to the endoplasmic reticulum, and lipid transport from the endoplasmic reticulum to the chloroplast envelope membranes. Transport of hydrophobic molecules through aqueous space is energetically unfavorable and must be catalyzed by dedicated enzymes, frequently on specialized membrane structures. Here, we review photosynthetic membrane lipid transport to the chloroplast in the context of photosynthetic membrane lipid synthesis. We independently consider the identity of transported lipids, the proteinaceous transport components, and membrane structures which may allow efficient transport. Recent advances in lipid transport of chloroplasts, bacteria, and other systems strongly suggest that lipid transport is achieved by multiple mechanisms which include membrane contact sites with specialized protein machinery. This machinery is likely to include the TGD1, 2, 3 complex with the TGD5 and TGD4/LPTD1 systems, and may also include a number of proteins with domains similar to other membrane contact site lipid-binding proteins. Importantly, the likelihood of membrane contact sites does not preclude lipid transport by other mechanisms including vectorial acylation and vesicle transport. Substantial progress is needed to fully understand all photosynthetic membrane lipid transport processes and how they are integrated.
光合膜为地球上的生命提供了大部分可用的能量。为了产生光合膜脂质，需要多个运输步骤，包括脂肪酸从叶绿体基质到内质网的输出，以及脂质从内质网到叶绿体被膜的运输。疏水分子通过水相的运输在能量上是不利的，必须由专门的酶催化，通常在专门的膜结构上进行。在这里，我们回顾了光合膜脂质在光合膜脂质合成背景下向叶绿体的运输。我们分别考虑了被运输脂质的特性、蛋白运输成分以及可能允许有效运输的膜结构。最近在叶绿体、细菌和其他系统的脂质运输方面的进展强烈表明，脂质运输是通过多种机制实现的，这些机制包括与专门蛋白机制的膜接触位点。该机制可能包括 TGD1、2、3 复合物以及 TGD5 和 TGD4/LPTD1 系统，还可能包括许多具有类似于其他膜接触位点脂质结合蛋白结构域的蛋白。重要的是，膜接触位点的可能性并不能排除其他机制的脂质运输，包括载体酰化和囊泡运输。需要取得实质性进展才能全面了解所有光合膜脂质运输过程以及它们是如何整合的。
