Targeting to the Vacuoles in Plant Cells

比较植物液泡蛋白的氨基酸序列表明，这些蛋白之间没有共同的序列，可以单独负责靶向液泡。因此，从不同蛋白质中分选信号的研究将需要理解这一过程中涉及的结构决定因素。禾本科植物凝集素是一种液泡蛋白，是最具特性的植物蛋白之一。这些凝集素的氨基酸序列、三维蛋白质结构和cDNA都是可用的。获得了能够正确表达和加工大麦凝集素的转基因烟草植株和悬浮培养物。这项研究未来五年的目标包括分析和表征负责向液泡分选的蛋白质序列，以及识别一个(或多个)可能的受体，该受体识别这些分选序列并随后介导蛋白质向空泡的运输。对大麦凝集素原蛋白的液泡分选信号进行鉴定和分析。一旦识别了分选信号，将解决以下问题：1)能够将报告蛋白重定向到液泡的最短序列是什么？2)分选结构域中负责正确靶向的特定氨基酸是什么？3)分选信号的二级结构重要吗？还将测定原大麦凝集素与其可能的受体(S)的结合特性。真核细胞中独立的亚细胞室的维持依赖于对新合成的蛋白质的正确分类和靶向。因此，必须在细胞中存在机制，以确保这些蛋白质靶向正确的细胞内膜。在植物中，许多蛋白质沉积在称为液泡的多功能细胞器中。这些蛋白质有助于液泡的溶酶体、储存和植物防御功能。这项研究的目的是了解蛋白质靶向植物细胞液泡的机制。这些结果将为植物细胞生物学中的这一重要问题提供重要的新信息。

Comparison of the amino acid sequences of plant vacuolar proteins indicates that there is no sequence in common among these proteins which can be solely responsible for targeting to vacuoles. Therefore, the study of sorting signals from different proteins will be required to understand the structural determinants involved in this process. Gramineae lectins, which are vacuolar proteins, are among the best characterized plant proteins. Amino acid sequences, 3-D protein structures, and cDNAs for these lectins are available. Transgenic tobacco plants and suspension cultures have been obtained which correctly express and process barley lectin. The goals of this research for the next five years include the analysis and characterization of protein sequences responsible for sorting to the vacuole and the identification of a putative receptor (or receptors) which recognizes these sorting sequences and subsequently mediates protein transport to vacuoles. The vacuolar sorting signal of the barley lectin proprotein will be identified and analyzed. Once the sorting signal is identified, the following questions will be addressed: 1) What is the shortest sequence capable of redirecting a reporter protein to the vacuole? 2) What are the specific amino acids within the sorting domain that are responsible for correct targeting? 3) Is secondary structure of the sorting signal important? The characteristics of binding of probarley lectin to its putative receptor(s) will also be determined. Maintenance of separate subcellular compartments in eukaryotic cells depends on the correct sorting and targeting of newly synthesized proteins. Thus, mechanisms must exist in the cell to assure that these proteins are targeted to the correct intracellular membranes. In plants, many proteins are deposited in multifunctional organelles called vacuoles. These proteins contribute to the lysosomal, storage, and plant defense functions of the vacuole. The goal of this research is to understand the mechanisms by which proteins are targeted to the plant cell vacuole. The results will contribute important new information on this important problem in plant cell biology.