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Identification of a probable pore forming domain in the multimeric vacuolar anion channel AtALMT9

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2013
Author Zang J, Bätz U, Krügel U, Martinoia E, De Angeli A,
Project ABC transporters involved in signalling events
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Original article (peer-reviewed)

Journal Plant Physiology
Volume (Issue) 163
Page(s) 830 - 843
Title of proceedings Plant Physiology
DOI doi:10.1104/pp.113.219832

Open Access

Type of Open Access Publisher (Gold Open Access)


Aluminum-activated malate transporters (ALMTs) form an important family of anion channels involved in fundamental physiological processes in plants. Because of their importance, the role of ALMTs in plant physiology is studied extensively. In contrast, the structural basis of their functional properties is largely unknown. This lack of information limits the understanding of the functional and physiological differences between ALMTs and their impact on anion transport in plants. This study aimed at investigating the structural organization of the transmembrane domain of the Arabidopsis (Arabidopsis thaliana) vacuolar channel AtALMT9. For that purpose, we performed a large-scale mutagenesis analysis and found two residues that form a salt bridge between the first and second putative transmembrane a-helices (TMa1 and TMa2). Furthermore, using a combination of pharmacological and mutagenesis approaches, we identified citrate as an “open channel blocker” of AtALMT9 and used this tool to examine the inhibition sensitivity of different point mutants of highly conserved amino acid residues. By this means, we found a stretch within the cytosolic moiety of the TMa5 that is a probable pore-forming domain. Moreover, using a citrate-insensitive AtALMT9 mutant and biochemical approaches, we could demonstrate that AtALMT9 forms a multimeric complex that is supposedly composed of four subunits. In summary, our data provide, to our knowledge, the first evidence about the structural organization of an ion channel of the ALMT family. We suggest that AtALMT9 is a tetramer and that the TMa5 domains of the subunits contribute to form the pore of this anion channel.