ABC TRANSPORTER

Biochemical characterization of the Arabidopsis ABC transporter AtABCB14 and exploring why it exhibits an import activity

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 Obiettivo del progetto (Objective)

'The genome of Arabidopsis thaliana is predicted to encode 129 ABC proteins, which are involved in many physiological processes such as transport of metabolites, toxic substance, and regulation of stomatal movement (Martinoia et al., 2001; Rea, 2007). The ABC protein AtABCB14 is implicated in the regulation of stomatal movement by transporting malate into guard cells (Lee et al. 2008). This is only the second plant ABC transporter shown to act as an importer and no animal counterpart has been shown to exhibit an import activity. The goal of this project is to carry out a detailed analysis of AtABCB14. To do this I will i) Characterize the kinetics and the substrate activities of AtABCB14; ii) Use site-directed mutagenesis and substrate-dependent ATP-hydrolysis to investigate whether the import activity is ATP-dependent; iii) Carry out experiments to find structural determinants which are responsible for the import activity of this ABC transporter. The identification of the biochemical properties and the import mechanism of AtABCB14 will be helpful to understand why only plants have ABC transporters exhibiting import activity. Furthermore, the identification of factors responsible for the import activity may provide important information to the medical field and cancer research.'

Introduzione (Teaser)

Studying membrane proteins in plants provided important insight into key physiological processes. European researchers generated information that could be exploited to maximise bioenergy production from plants.

Descrizione progetto (Article)

ABC transporters are transmembrane proteins that utilise the energy offered by ATP to perform various biological processes. One such process is the translocation of molecules (metabolites, toxic substances, ions) across membranes. In plants, ABC transporters regulate stomatal movement, the pores found in the epidermis of leaves.

Arabidopsis thaliana contains about 130 ABC proteins which participate in the transport of different substances. Understanding the mechanisms of hormone transport such as auxin is also important for breeding purposes and could further be exploited for biomass production.

In mammalian cells, ABC transporters confer resistance to drugs in cancer cells and also cause disease, such as in the case of cystic fibrosis. The EU-funded ABC TRANSPORTER project wished to analyse the sequence of ABC transporters in plants and associate it with their substrate specificity.

Considerable part of the work was devoted to the identification of the binding partner of the AtABCB14 importer protein which helps malate enter plant cells under high carbon dioxide concentrations. In search of transporters of weak acids in yeast, scientists identified two genes which confer acetic acid resistance. To investigate the impact of these genes on the plant phenotype, they generated mutants in the model plant Arabidopsis thaliana.

Knockout of the AtABCC8 gene induced a lower coniferin, monolignol glucoside content than that of wild type. This clearly indicated that ABC transporters have more than one substrate and that AtABCC8 could participate both in acid and monolignol glucoside transport. This may be helpful to understand the mechanism of lignin accumulation and enable the breeding of plants with reduced lignin content, suitable for bioenergy production.

Taken together, the results of the ABC TRANSPORTER study provide important insight into plant development and growth. Furthermore, given the medical importance of ABC transporters, the generated knowledge could be extrapolated to human cells and may help identify novel pharmaceutical targets.