Cell Biology of Iron Transport

Arn 1是一种整合的膜蛋白，介导酿酒酵母中铁色素（铁的重要营养来源）的吸收。在没有铁色素的情况下，Arn 1 p被直接从高尔基体网络分选到液泡腔进行降解。在低水平的铁色素的存在下，铁载体与Arn 1上的受体结构域结合，触发Arn 1重新分布到质膜。当细胞外铁色素水平高时，Arn 1在质膜和细胞内囊泡之间循环。为了进一步了解Arn 1 p的运输机制，我们使用合成基因阵列技术筛选了4580个活酵母缺失突变体的Arn 1-GFP错误定位。我们确定了100多个基因所需的跨高尔基体网络的空泡运输的Arn 1-GFP，只有两个基因，SER 1和SER 2，所需的铁色素诱导质膜运输的Arn 1-GFP。SER 1和SER 2编码主要丝氨酸生物合成途径的两种酶，并且用补充丝氨酸或甘氨酸校正ser 1菌株中的Arn 1运输缺陷。Hxt 3是一种结构相关的葡萄糖转运蛋白，其质膜转运不受SER 1缺失的影响。丝氨酸是合成多种细胞成分所必需的，包括嘌呤、鞘脂和磷脂，但其中只有磷脂酰丝氨酸纠正了Ser 1菌株的Arn 1运输缺陷。磷脂合成缺陷的菌株也表现出改变Arn 1 p贩运，这表明一些转运蛋白的细胞内贩运依赖于细胞膜的磷脂组成。

Arn1 is an integral membrane protein that mediates the uptake of ferrichrome, an important nutritional source of iron, in Saccharomyces cerevisiae. In the absence of ferrichrome, Arn1p is sorted directly from the trans-Golgi network to the vacuolar lumen for degradation. In the presence of low levels of ferrichrome, the siderophore binds to a receptor domain on Arn1, triggering the redistribution of Arn1 to the plasma membrane. When extracellular ferrichrome levels are high, Arn1 cycles between the plasma membrane and intracellular vesicles. To further understand the mechanisms of trafficking of Arn1p, we screened 4580 viable yeast deletion mutants for mislocalization of Arn1-GFP using synthetic genetic array technology. We identified over 100 genes required for trans-Golgi network-to-vacuole trafficking of Arn1-GFP, and only two genes, SER1 and SER2, required for the ferrichrome-induced plasma membrane trafficking of Arn1-GFP. SER1 and SER2 encode two enzymes of the major serine biosynthetic pathway, and the Arn1 trafficking defect in the ser1∆ strain was corrected with supplemental serine or glycine. Plasma membrane trafficking of Hxt3, a structurally related glucose transporter, was unaffected by SER1 deletion. Serine is required for the synthesis of multiple cellular components, including purines, sphingolipids, and phospholipids, but of these only phosphatidylserine corrected the Arn1 trafficking defects of the ser1∆ strain. Strains with defects in phospholipid synthesis also exhibited alterations in Arn1p trafficking, indicating that the intracellular trafficking of some transporters is dependent on the phospholipid composition of the cellular membranes.