cleavage of acyl CoA by ABC subfamily D transporters in peroxisomes: mechanism and functional roles

动物、植物和真菌的细胞被组织成具有不同功能的隔间，就像房子里的房间一样。其中一个隔间就是过氧化物体。过氧体的主要作用是从储存的脂肪和油中释放能量和分子构件，这一过程被称为β-氧化。在制造细胞内和细胞之间的重要信号的分子方面，β-氧化也起着其他作用，而过氧化物体在细胞中与不同的隔室共享其他几项工作。为了有效地工作，许多不同类型的分子必须以有组织的方式进出过氧化物体。因此，过氧化物体有时被称为“十字路口的细胞器”。这个项目的目的是研究一类蛋白质，这些蛋白质将分子运输到过氧化体中，以便它们可以通过β-氧化进行处理。这些蛋白质被称为D亚家族的ATP结合盒转运体，或ABCD转运体。我们一直在详细研究这些转运蛋白是如何工作的，并在更广泛的范围内研究，以确定它们如何帮助控制细胞的不同化学反应。通过对ABCD转运蛋白的研究，我们了解到β-氧化对植物种子的萌发和建立、育性、衰老、根的生长和伤害反应是重要的，这告诉我们转运蛋白可以接受相当广泛的不同分子。其他人则表明，ABCD转运蛋白对人类脂肪分解很重要，当它们不能正常工作时，会导致疾病。最近，我们发现ABCD转运蛋白是相当不寻常的，因为它们接受一个分子，如脂肪酸，该分子与另一个称为辅酶A(CoA)的分子相连，然后随着脂肪酸被运输到过氧化体中，将CoA部分砍掉。辅酶A是细胞中一种重要的化学物质，因为它有助于不同的化学反应发生，因此需要仔细调节不同隔室中的水平。一旦进入过氧化酶体，脂肪酸就不能进入β-氧化过程，直到它被“激活”--通过连接到另一个辅酶A分子。乍一看，这似乎效率很低，但我们认为，这对于控制哪些分子可以进入过氧化酶体并被β-氧化处理(这被称为“代谢通道”)很重要。CoA分子与过氧化物酶体内的脂肪酸重新连接需要一种名为酰基活化酶(AAEs)的蛋白质。我们已经证明，植物中的ABCD转运蛋白在物理上和功能上都与将脂肪酸连接到辅酶A的AAEs相连，但我们认为它们也可以与不同的AAEs相互作用，这些AAEs将其他类型的分子连接到CoA。不同AAE的可用性及其与转运体的相互作用为控制哪些分子被β氧化处理提供了一个潜在的检查点。为了更好地了解这一过程并使知识更广泛地有用，我们现在需要了解转运体如何工作的更多细节，包括CoA裂解如何适应运输过程，以及它是否对可以进口的不同分子起到同样好的作用。我们还想找出被切割的辅酶A最终在哪里(在过氧化物体外面还是在里面？)。总而言之，这些信息将告诉我们，过氧化酶体如何在不同的竞争功能之间平衡他们的资源，以及新陈代谢是如何受到控制的。

Cells of animals, plants and fungi are organised into compartments which have different functions, much like the rooms in a house. One such compartment is the peroxisome. The main role of peroxisomes is to release energy and molecular building blocks from stored fat and oil, a process called beta-oxidation. Beta-oxidation also plays other roles in making molecules that are important signals within and between cells and peroxisomes share several other jobs with different compartments in cells. For this to work efficiently, many different types of molecules have to move in and out of peroxisomes in an organised fashion. Thus, peroxisomes are sometimes called "organelles at the crossroads". This project aims to study a family of proteins which transport molecules into peroxisomes so that they can be processed by beta-oxidation. These proteins are called ATP Binding Cassette transporters from subfamily D, or ABCD transporters. We have been studying how these transporters work at a detailed level and also more globally, to determine how they help to keep the different chemical reactions of the cell in check. By investigating ABCD transporters, we have learned that beta-oxidation is important for seed germination and establishment, fertility, senescence, root growth and wound responses in plants and this tells us that the transporters accept quite a wide range of different molecules. Others have shown that ABCD transporters are important for fat breakdown in humans and when they do not work properly, can cause diseases. Recently, we have found that ABCD transporters are rather unusual because they accept a molecule such as a fatty acid which is joined to another molecule called Coenzyme A (CoA) but then chop off ("cleave") the CoA part as the fatty acid is transported into the peroxisome. CoA is an important chemical in cells because it helps different chemical reactions to happen, thus the levels in different compartments need to be carefully regulated. Once inside the peroxisome, the fatty acid cannot enter the beta-oxidation process until it is "activated"- by joining it to another CoA molecule. At first glance, this seems inefficient but we think that it is important for controlling which molecules can enter the peroxisome and be processed by beta-oxidation (this is known as "metabolic channelling"). Re-joining of the CoA molecule to fatty acids inside the peroxisome requires proteins called acyl activating enzymes (AAEs). We have shown that ABCD transporters in plants are physically and functionally linked to the AAEs which join fatty acids to CoA but we think that they could also interact with different AAEs which join other kinds of molecules to CoA. The availability of different AAEs and their interaction with the transporter provides a potential check-point to control which molecules are allowed to be processed by beta-oxidation.To understand this process better and to make the knowledge more widely useful, we now need to know more detail about how the transporters work, including how the CoA cleavage fits into the transport process and whether it works equally well for different molecules which can be imported. We also want to find out where the cleaved CoA ends up (outside the peroxisome or inside?). Taken together, this information will tell us how peroxisomes balance their resources between different competing functions and how metabolism is controlled.