Functional characterization and organ distribution of three mitochondrial ATP–Mg/Pi carriers in Arabidopsis thaliana

Abstract

The Arabidopsis thaliana genome contains 58 membrane proteins belonging to the mitochondrial carrier family. Three members of this family, here named AtAPC1, AtAPC2, and AtAPC3, exhibit high structural similarities to the human mitochondrial ATP-Mg(2+)/phosphate carriers. Under normal physiological conditions the AtAPC1 gene was expressed at least five times more than the other two AtAPC genes in flower, leaf, stem, root and seedlings. However, in stress conditions the expression levels of AtAPC1 and AtAPC3 change. Direct transport assays with recombinant and reconstituted AtAPC1, AtAPC2 and AtAPC3 showed that they transport phosphate, AMP, ADP, ATP, adenosine 5'-phosphosulfate and, to a lesser extent, other nucleotides. AtAPC2 and AtAPC3 also had the ability to transport sulfate and thiosulfate. All three AtAPCs catalyzed a counter-exchange transport that was saturable and inhibited by pyridoxal-5'-phosphate. The transport activities of AtAPCs were also inhibited by the addition of EDTA or EGTA and stimulated by the addition of Ca(2+). Given that phosphate and sulfate can be recycled via their own specific carriers, these findings indicate that AtAPCs can catalyze net transfer of adenine nucleotides across the inner mitochondrial membrane in exchange for phosphate (or sulfate), and that this transport is regulated both at the transcriptional level and by Ca(2+).

ATP sensing in living plant cells reveals tissue gradients and stress dynamics of energy physiology

“…With the exception of one report on cell death induced by hypersensitive response (Hatsugai et al, 2012), fluorescence ATP measurements have been lacking in plant research. Live-cell fluorescent monitoring complements widespread standard approaches, such as luminescent or HPLC-based ATP determinations in biological extracts, or radioisotope-based techniques for membrane transport assays (Manfredi et al, 2002; Khlyntseva et al, 2009; Lorenz et al, 2015; Monné et al, 2015). While those techniques offer high sensitivity and accuracy in quantifying ATP, and other nucleotides, in extracts, they provide endpoint measurements after removal from the functional biological system and have limited use for resolving the ATP concentration over time at the (sub)cellular and tissue level.…”

Uncoupling proteins 1 and 2 (UCP1 and UCP2) from Arabidopsis thaliana are mitochondrial transporters of aspartate, glutamate, and dicarboxylates

“…Arabidopsis has been demonstrated to express MCs for the four main types of substrates (1) (i.e. nucleotide carriers for ADP/ATP (AAC1-4, PNC1 and -2, AtBT1, PM-ANT1, and TAAC) (10 -16), adenine nucleotides (ADNT1) (17), ATP-Mg/P i (APC1-3) (18,19), NAD ϩ (NDT1 and -2) (20), NAD ϩ , NADH, CoA, and adenosine 3Ј,5Ј-phosphate (PXN) (21,22); carboxylate carriers for di-and tricarboxylates (DTC) (23) and dicarboxylates (DIC1-3) (24); amino acid carriers for basic amino acids (BAC1 and -2) (25,26) and S-adenosylmethionine (SAMC1 and -2) (27,28); and inorganic ion carriers for phosphate and sulfate (29)). It is important to note that some of the carriers characterized from Arabidopsis have broader substrate specificities than their human and yeast counterparts, and additionally some of them are localized in compartments other than the mitochondria, such as peroxisomes, chloroplasts, the endoplasmic reticulum, and the plasma membrane (1).…”

Calcium regulation of the human mitochondrial ATP-Mg/Pi carrier SLC25A24 uses a locking pin mechanism

“…The effect of calcium regulation on the transport activity of APC has been studied in isolated rat liver mitochondria20, isolated yeast mitochondria321 and more recently in liposomes with reconstituted Arabidopsis thaliana APC2223. Furthermore, the effect of calcium on adenine nucleotide uptake into mitochondria of human osteosarcoma cells has been studied in which APC1 (SCaMC1/ SLC25A24 ) is the major isoform11.…”