Abstract
Multidrug and toxic compound extrusion (MATE) transporters in eukaryotes have been characterized to be antiporters that mediate the transport of substrates in exchange for protons. In plants, alkaloids, phytohormones, ion chelators, and flavonoids have been reported to be the substrates of MATE transporters. Structural analyses have been conducted to dissect the functional significance of various motifs of MATE proteins. However, an understanding of the functions of the N- and C-termini has been inadequate. Here, by performing phylogenetic analyses and protein sequence alignment of 14 representative plant species, we identified a distinctive N-terminal poly-glutamate motif among a cluster of MATE proteins in soybean. Amongst them, GmMATE4 has the most consecutive glutamate residues at the N-terminus. A subcellular localization study showed that GmMATE4 was localized at the vacuolar membrane-like structure. Protein charge prediction showed that the mutation of the glutamate residues to alanine would reduce the negative charge at the N-terminus. Using yeast as the model, we showed that GmMATE4 mediated the transport of daidzein, genistein, glycitein, and glycitin. In addition, the glutamate-to-alanine mutation reduced the isoflavone transport capacity of GmMATE4. Altogether, we demonstrated GmMATE4 as an isoflavone transporter and the functional significance of the N-terminal poly-glutamate motif of GmMATE4 for regulating the isoflavone transport activity.
Highlights
Multidrug and toxic compound extrusion (MATE) transporters are a family of active membrane transporters generally consisting of 12 transmembrane domains (TMDs) [1]
Through phylogenetic analyses of MATE proteins from 14 representative plant species, including those in the Leguminosae family (Arachis ipaensis, Cajanus cajan, Cicer arietinum, Lotus japonicus, Medicago truncatula, Phaseolus vulgaris, Vigna radiata and Glycine max) and other non-Leguminosae species (Arabidopsis thaliana, Gossypium hirsutum, Helianthus annuus, Oryza sativa, Solanum lycopersicum, and Solanum tuberosum), we found clades enriched with MATE proteins from Leguminosae and a cluster consisting solely of MATE proteins from Glycine max
In order to gain insights into the structures of MATE proteins, we performed a phylogenetic analysis of MATE proteins from 14 representative plant species including some in the Leguminosae group (Arachis ipaensis, Cajanus cajan, Cicer arietinum, Lotus japonicus, Medicago truncatula, Phaseolus vulgaris, Vigna radiata, and Glycine max) and others in the non-Leguminosae group (Arabidopsis thaliana, Gossypium hirsutum, Helianthus annuus, Oryza sativa, Solanum lycopersicum, and Solanum tuberosum) which have a Benchmarking sets of Universal Single-Copy Orthologs (BUSCO) index [28] of their genomes higher than 85 (Figure 1)
Summary
Multidrug and toxic compound extrusion (MATE) transporters are a family of active membrane transporters generally consisting of 12 transmembrane domains (TMDs) [1]. MATE transporters have been reported to be localized at membranes including plasma, vacuolar, and mitochondrial membranes, the chloroplast envelope, and the surface of small vesicles [1]. MATE proteins are generally characterized by the typical 12 TMDs [5]. The different amino acid residues of different MATE proteins enable different substrate specificities [1,6,7]. MATE transporters have been reported to be responsible for the movement of alkaloids, phytohormones, ion chelators, and flavonoids including anthocyanins and isoflavones across membranes [1,6,7,8,9].
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