Identification and Characterization of a Novel Plastidic Adenine Nucleotide Uniporter from Solanum tuberosum

Michaela Leroch,Simon Kirchberger,Ilka Haferkamp,Markus Wahl,H Ekkehard Neuhaus,Joachim Tjaden

doi:10.1074/jbc.m412462200

Michaela Leroch, Simon Kirchberger + Show 4 more

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https://doi.org/10.1074/jbc.m412462200

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Abstract

Homologs of BT1 (the Brittle1 protein) are found to be phylogenetically related to the mitochondrial carrier family and appear to occur in both mono- and dicotyledonous plants. Whereas BT1 from cereals is probably involved in the transport of ADP-glucose, which is essential for starch metabolism in endosperm plastids, BT1 from a noncereal plant, Solanum tuberosum (StBT1), catalyzes an adenine nucleotide uniport when functionally integrated into the bacterial cytoplasmic membrane. Import studies into intact Escherichia coli cells harboring StBT1 revealed a narrow substrate spectrum with similar affinities for AMP, ADP, and ATP of about 300-400 mum. Transiently expressed StBT1-green fluorescent protein fusion protein in tobacco leaf protoplasts showed a plastidic localization of the StBT1. In vitro synthesized radioactively labeled StBT1 was targeted to the envelope membranes of isolated spinach chloroplasts. Furthermore, we showed by real time reverse transcription-PCR a ubiquitous expression pattern of the StBT1 in autotrophic and heterotrophic potato tissues. We therefore propose that StBT1 is a plastidic adenine nucleotide uniporter used to provide the cytosol and other compartments with adenine nucleotides exclusively synthesized inside plastids.

Highlights

Plastids are semiautonomous plant organelles existing in a wide range of differential forms depending on the developmental stage and function of the cells in which they reside
Whereas BT1 from cereals is probably involved in the transport of ADP-glucose, which is essential for starch metabolism in endosperm plastids, BT1 from a noncereal plant, Solanum tuberosum (StBT1), catalyzes an adenine nucleotide uniport when functionally integrated into the bacterial cytoplasmic membrane
Identification of a Plastidic Adenine Nucleotide Uniporter sequence was aligned with BT1 homologs from maize (Zea mays), barley (Hordeum vulgare), and A. thaliana (Fig. 1)

Summary

Introduction

Plastids are semiautonomous plant organelles existing in a wide range of differential forms depending on the developmental stage and function of the cells in which they reside They are the sites of photosynthesis and harbor exclusively many biosynthetic pathways such as synthesis of starch and amino and fatty acids [1]. The plastidic phosphate translocators differ from several other transporters of the plastidic envelope membrane, which function as monomers that contain 12 transmembrane helices These include a maltose transporter that exports maltose, the product of hydrolytic starch degradation [9], two dicarboxylate translocators that are involved in ammonia assimilation [10], and a Hϩ/Pi symporter that affects Pi allocation within the plant [11]. The ATP required for the AGPase reaction is imported into these plastids via the plastidic NTT in counter exchange for ADP [12, 20]

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