Plant Proton Pumps and Cytosolic pH-Homeostasis

Proton pumps create a proton motif force and thus, energize secondary active transport at the plasma nmembrane and endomembranes of the secretory pathway. In the plant cell, the dominant proton pumps are the plasma membrane ATPase, the vacuolar pyrophosphatase (V-PPase), and the vacuolar-type ATPase (V-ATPase). All these pumps act on the cytosolic pH by pumping protons into the lumen of compartments or into the apoplast. To maintain the typical pH and thus, the functionality of the cytosol, the activity of the pumps needs to be coordinated and adjusted to the actual needs. The cellular toolbox for a coordinated regulation comprises 14-3-3 proteins, phosphorylation events, ion concentrations, and redox-conditions. This review combines the knowledge on regulation of the different proton pumps and highlights possible coordination mechanisms.

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pH-dependent Cargo Sorting from the Golgi

Journal of Biological Chemistry ◽

10.1074/jbc.m110.197889 ◽

2011 ◽

Vol 286 (12) ◽

pp. 10058-10065 ◽

Cited By ~ 34

Author(s):

Chunjuan Huang ◽

Amy Chang

Keyword(s):

Plasma Membrane ◽

Membrane Proteins ◽

Atpase Activity ◽

Secretory Pathway ◽

Ph Dependence ◽

Glucose Deprivation ◽

Ph Homeostasis ◽

Plasma Membrane Proteins ◽

Cytosolic Ph ◽

Cargo Sorting

The vacuolar proton-translocating ATPase (V-ATPase) plays a major role in organelle acidification and works together with other ion transporters to maintain pH homeostasis in eukaryotic cells. We analyzed a requirement for V-ATPase activity in protein trafficking in the yeast secretory pathway. Deficiency of V-ATPase activity caused by subunit deletion or glucose deprivation results in missorting of newly synthesized plasma membrane proteins Pma1 and Can1 directly from the Golgi to the vacuole. Vacuolar mislocalization of Pma1 is dependent on Gga adaptors although no Pma1 ubiquitination was detected. Proper cell surface targeting of Pma1 was rescued in V-ATPase-deficient cells by increasing the pH of the medium, suggesting that missorting is the result of aberrant cytosolic pH. In addition to mislocalization of the plasma membrane proteins, Golgi membrane proteins Kex2 and Vrg4 are also missorted to the vacuole upon loss of V-ATPase activity. Because the missorted cargos have distinct trafficking routes, we suggest a pH dependence for multiple cargo sorting events at the Golgi.

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Secretory vesicles externalize the major plasma membrane ATPase in yeast.

The Journal of Cell Biology ◽

10.1083/jcb.106.3.641 ◽

1988 ◽

Vol 106 (3) ◽

pp. 641-648 ◽

Cited By ~ 39

Author(s):

C L Holcomb ◽

W J Hansen ◽

T Etcheverry ◽

R Schekman

Keyword(s):

Plasma Membrane ◽

Secretory Pathway ◽

Biochemical Characterization ◽

Plasma Membrane Atpase ◽

Membrane Assembly ◽

Yeast Cell Surface ◽

Membrane Atpase ◽

Constitutive Secretion ◽

Secretory Enzyme

Yeast cell surface growth is accomplished by constitutive secretion and plasma membrane assembly, culminating in the fusion of vesicles with the bud membrane. Coordination of secretion and membrane assembly has been investigated by examining the biogenesis of plasma membrane ATPase (PM ATPase) in secretion-defective (sec) strains of Saccharomyces cerevisiae. PM ATPase is synthesized as a approximately 106-kD polypeptide that is not detectably modified by asparagine-linked glycosylation or proteolysis during transit to the plasma membrane. Export of the PM ATPase requires the secretory pathway. In sec1, a mutant defective in the last step of secretion, large amounts of Golgi-derived vesicles are accumulated. Biochemical characterization of this organelle has demonstrated that PM ATPase and the secretory enzyme, acid phosphatase, are transported in a single vesicle species.

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Faculty Opinions recommendation of Vacuolar and plasma membrane proton pumps collaborate to achieve cytosolic pH homeostasis in yeast.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.13484989.14862108 ◽

2012 ◽

Author(s):

Christopher Loewen

Keyword(s):

Plasma Membrane ◽

Proton Pumps ◽

Ph Homeostasis ◽

Cytosolic Ph

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An Endosome-to-Plasma Membrane Pathway Involved in Trafficking of a Mutant Plasma Membrane ATPase in Yeast

Molecular Biology of the Cell ◽

10.1091/mbc.11.2.579 ◽

2000 ◽

Vol 11 (2) ◽

pp. 579-592 ◽

Cited By ~ 56

Author(s):

Wen-jie Luo ◽

Amy Chang

Keyword(s):

Plasma Membrane ◽

Cell Surface ◽

Secretory Pathway ◽

Protein Sorting ◽

Temperature Sensitive ◽

Plasma Membrane Atpase ◽

Vacuolar Protein Sorting ◽

Membrane Atpase ◽

Vacuolar Protein ◽

Endosomal System

The plasma membrane ATPase, encoded by PMA1, is delivered to the cell surface via the secretory pathway. Previously, we characterized a temperature-sensitive pma1 mutant in which newly synthesized Pma1-7 is not delivered to the plasma membrane but is mislocalized instead to the vacuole at 37°C. Severalvps mutants, which are defective in vacuolar protein sorting, suppress targeting-defective pma1 by allowing mutant Pma1 to move once again to the plasma membrane. In this study, we have analyzed trafficking in the endosomal system by monitoring the movement of Pma1-7 in vps36, vps1, andvps8 mutants. Upon induction of expression, mutant Pma1 accumulates in the prevacuolar compartment in vps36cells. After chase, a fraction of newly synthesized Pma1-7 is delivered to the plasma membrane. In both vps1 andvps8 cells, newly synthesized mutant Pma1 appears in small punctate structures before arrival at the cell surface. Nevertheless, biosynthetic membrane traffic appears to follow different routes in vps8 and vps1: the vacuolar protein-sorting receptor Vps10p is stable in vps8 but not in vps1. Furthermore, a defect in endocytic delivery to the vacuole was revealed in vps8 (andvps36) but not vps1 by endocytosis of the bulk membrane marker FM 4-64. Moreover, in vps8 cells, there is defective down-regulation from the cell surface of the mating receptor Ste3, consistent with persistent receptor recycling from an endosomal compartment to the plasma membrane. These data support a model in which mutant Pma1 is diverted from the Golgi to the surface invps1 cells. We hypothesize that in vps8and vps36, in contrast to vps1, mutant Pma1 moves to the surface via endosomal intermediates, implicating an endosome-to-surface traffic pathway.

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Ubiquitin-mediated Targeting of a Mutant Plasma Membrane ATPase, Pma1-7, to the Endosomal/Vacuolar System in Yeast

Molecular Biology of the Cell ◽

10.1091/mbc.e03-10-0727 ◽

2004 ◽

Vol 15 (5) ◽

pp. 2401-2409 ◽

Cited By ~ 52

Author(s):

Maddalena Pizzirusso ◽

Amy Chang

Keyword(s):

Plasma Membrane ◽

Cell Surface ◽

Ubiquitin Ligase ◽

Secretory Pathway ◽

Protein Transport ◽

Plasma Membrane Atpase ◽

Membrane Atpase ◽

Endosomal Pathway ◽

Quality Control Mechanism ◽

Vacuolar System

Pma1-7 is a mutant plasma membrane ATPase that is impaired in targeting to the cell surface at 37°C and is delivered instead to the endosomal/vacuolar pathway for degradation. We have proposed that Pma1-7 is a substrate for a Golgibased quality control mechanism. By contrast with wild-type Pma1, Pma1-7 is ubiquitinated. Ubiquitination and endosomal targeting of Pma1-7 is dependent on the Rsp5-Bul1-Bul2 ubiquitin ligase protein complex but not the transmembrane ubiquitin ligase Tul1. Analysis of Pma1-7 ubiquitination in mutants blocked in protein transport at various steps of the secretory pathway suggests that ubiquitination occurs after ER exit but before endosomal entry. In the absence of ubiquitination in rsp5-1 cells, Pma1-7 is delivered to the cell surface and remains stable. Nevertheless, Pma1-7 remains impaired in association with detergent-insoluble glycolipid-enriched complexes in rsp5-1 cells, suggesting that ubiquitination is not the cause of Pma1-7 exclusion from rafts. In vps1 cells in which protein transport into the endosomal pathway is blocked, Pma1-7 is routed to the cell surface. On arrival at the plasma membrane in vps1 cells, Pma1-7 remains stable and its ubiquitination disappears, suggesting deubiquitination activity at the cell surface. We suggest that Pma1-7 sorting and fate are regulated by ubiquitination.

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