Interplay of vacuolar transporters for coupling primary and secondary active transport

Michèle Siek,Chris M Ehring,Michael Liebthal,Derya Kirasi,Berenice Marg,Thorsten Seidel

doi:10.3934/biophy.2016.4.479

Michèle Siek, Chris M Ehring + Show 4 more

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https://doi.org/10.3934/biophy.2016.4.479

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Journal: AIMS Biophysics	Publication Date: Jan 1, 2016
Citations: 2	License type: cc-by

Affiliation: Bielefeld University

Abstract

Secondary active transporters are driven by the proton motif force which is generated by primary active transporters such as the vacuolar proton pumps V-ATPase and V-PPase. The vacuole occupies up to 90 % of the mature cell and acidification of the vacuolar lumen is a challenging and energy-consuming task for the plant cell. Therefore, a direct coupling of primary and secondary active transporters is expected to enhance transport efficiency and to reduce energy consumption by transport processes across the tonoplast. This has been addressed by analyzing physical and functional interactions between the V-ATPase and a selection of vacuolar transporters including the primary active proton pump AVP1, the calcium ion/proton exchanger CAX1, the potassium ion/proton symporter KUP5, the sodium ion/proton exchanger NHX1, and the anion/proton exchanger CLC-c. Physical interaction was demonstrated in vivo for the V-ATPase and the secondary active transporters CAX1 and CLC-c, which are responsible for calcium- and anion-accumulation in the vacuole, respectively. Measurements of V-ATPase activity and vacuolar pH revealed a functional interaction of V-ATPase and CAX1, CLC-c that is likely caused by the observed physical interaction. The complex of the V-ATPase further interacts with the nitrate reductase 2, and as a result, nitrate assimilation is directly linked to the energization of vacuolar nitrate accumulation by secondary active anion/proton exchangers.

Highlights

Secondary active transporters are driven by the proton motif force which is generated by primary active transporters such as the vacuolar proton pumps V-ATPase and vacuolar proton-translocating pyrophospatase (V-PPase)
The available published data on CAX1, NHX1, AVP1 and the co-expression analysis resulted in the selection of the transporters CAX1, NHX1, AVP1, KUP5 and CLC-c
The secondary active transporters NHX1, KUP5, CLC-c and CAX1 and the proton pump AVP1 were tested for their interaction with the V-ATPase

Summary

Introduction

With up to 90% of the cellular volume the plant vacuolar system represents the largest compartment group within plant cells and serves as storage compartment, disposal for waste and toxins, lytic compartment, Ca2+-store, and represents an important factor for plant growth and apoptosis [1,2]. The V-PPase pumps protons into vacuoles during embryo and seedling development, the V-ATPase takes over with increasing age of the plant cell and becomes the dominant proton pump for vegetative growth [10,11] This arrangement pays attention to the availability of ATP and PPi during development and might be a consequence of the complex structure of the V-ATPase: The V-ATPase is a multimeric complex of more than 800 kDa, which can be divided into a membrane integral sector VO (subunits VHA-a, VHA-c, VHA-c”, VHA-d, VHA-e) and a membrane associated sector V1 (subunits VHA-A–VHA-H) [2]. Kinases such as the WNK8 in Arabidopsis thaliana and CDPK1 in barley phosphorylate individual VHA-subunits such as VHA-a, VHA-C, and AIMS Biophysics

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