Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario, Canada.
mBio. 2021 Oct 26;12(5):e0099421. doi: 10.1128/mBio.00994-21. Epub 2021 Sep 21.
Polyphosphates (polyP) are energy-rich polymers of inorganic phosphates assembled into chains ranging from 3 residues to thousands of residues in length. They are thought to exist in all cells on earth and play roles in an eclectic mix of functions ranging from phosphate homeostasis to cell signaling, infection control, and blood clotting. In the budding yeast Saccharomyces cerevisiae, polyP chains are synthesized by the vacuole-bound vacuolar transporter chaperone (VTC) complex, which synthesizes polyP while simultaneously translocating it into the vacuole lumen, where it is stored at high concentrations. VTC's activity is promoted by an accessory subunit called Vtc5. In this work, we found that the conserved AP-3 complex is required for proper Vtc5 localization to the vacuole membrane. In human cells, previous work has demonstrated that mutation of AP-3 subunits gives rise to Hermansky-Pudlak syndrome, a rare disease with molecular phenotypes that include decreased polyP accumulation in platelet dense granules. In yeast AP-3 mutants, we found that Vtc5 is rerouted to the vacuole lumen by the ndosomal orting omplex equired for ransport (ESCRT), where it is degraded by the vacuolar protease Pep4. Cells lacking functional AP-3 have decreased levels of polyP, demonstrating that membrane localization of Vtc5 is required for its VTC stimulatory activity Our work provides insight into the molecular trafficking of a critical regulator of polyP metabolism in yeast. We speculate that AP-3 may also be responsible for the delivery of polyP regulatory proteins to platelet dense granules in higher eukaryotes. Long polymers of inorganic phosphates called polyphosphates are ubiquitous across biological kingdoms. From bacteria to humans, they have diverse functions related to protein homeostasis, energy metabolism, and cell signaling. In this study, we provide new insights into the intracellular trafficking of the polyphosphate biosynthetic machinery in the budding yeast S. cerevisiae. The critical advances of the work are 2-fold. First, it provides an explanation for decreased polyphosphate levels observed in cells mutated for a conserved intracellular trafficking machine. Second, it defines critical pathways that are highly likely to serve as hubs for polyphosphate regulation in yeast and other species.
多聚磷酸盐（polyP）是由无机磷酸盐组装而成的长链聚合物，其长度从 3 个残基到数千个残基不等。它们被认为存在于地球上的所有细胞中，并在从磷酸盐稳态到细胞信号传导、感染控制和血液凝结等各种功能中发挥作用。在出芽酵母酿酒酵母中，多聚磷酸盐链由液泡结合的液泡转运蛋白伴侣（VTC）复合物合成，该复合物在将多聚磷酸盐同时转运到液泡腔室中储存的同时合成多聚磷酸盐，在那里它以高浓度储存。VTC 的活性由称为 Vtc5 的辅助亚基促进。在这项工作中，我们发现保守的 AP-3 复合物是多聚磷酸盐正确定位于液泡膜所必需的。在人类细胞中，先前的工作表明，AP-3 亚基的突变导致 Hermansky-Pudlak 综合征，这是一种罕见的疾病，其分子表型包括血小板致密颗粒中多聚磷酸盐积累减少。在酵母 AP-3 突变体中，我们发现 Vtc5 被内体分拣复合物（ESCRT）重新定向到液泡腔室，在那里它被液泡蛋白酶 Pep4 降解。缺乏功能性 AP-3 的细胞中多聚磷酸盐水平降低，表明 Vtc5 的膜定位对于其 VTC 刺激活性是必需的。我们的工作为酵母中多聚磷酸盐代谢关键调节剂的分子运输提供了深入了解。我们推测，AP-3 也可能负责将多聚磷酸盐调节蛋白递送到高等真核生物的血小板致密颗粒中。
长链无机磷酸盐称为多聚磷酸盐在生物界中无处不在。从细菌到人类，它们具有与蛋白质稳态、能量代谢和细胞信号传导相关的多种功能。在这项研究中，我们提供了关于出芽酵母 S. cerevisiae 中多聚磷酸盐生物合成机制的细胞内运输的新见解。这项工作的关键进展有两个方面。首先，它解释了细胞中保守的细胞内运输机器突变导致的多聚磷酸盐水平降低的现象。其次，它定义了关键途径，这些途径很可能是酵母和其他物种中多聚磷酸盐调节的枢纽。
