A PQ-loop protein Ypq2 is involved in the exchange of arginine and histidine across the vacuolar membrane of Saccharomyces cerevisiae

Abstract

In nutrient-rich conditions, basic amino acids are actively accumulated into the vacuoles by H+-coupled transporters in Saccharomyces cerevisiae. In addition to the H+-coupled systems, the existence of an exchanger for arginine and histidine was indicated by kinetic analysis using isolated vacuolar membrane vesicles; however, the gene(s) involved in the activity has not been identified. Here, we show that the uptake activity of arginine driven by an artificially imposed histidine gradient decreased significantly by the disruption of the gene encoding vacuolar PQ-loop protein Ypq2, but not by those of Ypq1 and Ypq3. The exchange activity was restored by the expression of YPQ2. Furthermore, the substitution of a conserved proline residue, Pro29, in Ypq2 greatly decreased the exchange activity. These results suggest that Ypq2 is responsible for the exchange activity of arginine and histidine across the vacuolar membrane, and the conserved proline residue in the PQ-loop motif is required for the activity.

Nitrogen coordinated import and export of arginine across the yeast vacuolar membrane

“…In contrast, loading the vesicles with His was found to drive high Arg uptake (Fig 3C). This is in agreement with a report published during finalization of this paper, showing that Ypq2-catalyzed Arg uptake into vacuole-derived vesicles is stimulated by luminal His [9].…”

“…This LAAT-1-catalyzed transport was abolished when the conserved proline residue in the first PQ-loop of the protein was mutated to leucine [ 42 ]. A similar effect was reported for Ypq2 when an alanine was substituted for the corresponding residue (Pro29), highlighting the close similarity between PQLC2, LAAT-1 and Ypq2, and further indicating that Ypq2, like its orthologs, is an Arg transporter [ 9 ]. As for Vsb1, however, reconstitution of the purified protein in proteoliposomes is needed to fully characterize the transport activity of Ypq2.…”

“…The canavanine resistance phenotype of the ypq2Δ mutant can be suppressed by expression of PQLC2, shown to also recognize the Arg analog, suggesting that Ypq2 likewise functions as a vacuolar exporter of cationic amino acids [ 5 ]. Since this discovery, however, investigators have reported experiments on reconstituted vacuolar vesicles showing that Ypq1 and Ypq3 respectively catalyze Lys and histidine (His) uptake into the vacuole and that their activity depends on the H + gradient established by the V-ATPase [ 7 , 8 ], while Ypq2 catalyzes Arg/His exchange [ 9 ]. Another study reported that Ypq1, under Lys starvation conditions, is targeted to the vacuolar lumen and degraded, a result supporting a role of Ypq1 in Lys uptake into the vacuole [ 10 , 11 ].…”

“…More recently, Avt4 has been reported to function as a secondary active exporter of basic amino acids [ 14 ] and, depending on the experimental conditions, the Avt1 neutral amino acid transporter also seems able to import His [ 15 , 16 ]. During finalization of this manuscript, Ypq2 was reported to catalyze Arg uptake coupled to His efflux [ 9 ]. Overall, the respective roles and relative importance of transporters mediating influx and efflux of basic amino acids across the yeast vacuolar membrane remain poorly understood.…”

The Structure of the Membrane Protein of SARS-CoV-2 Resembles the Sugar Transporter SemiSWEET

“…The SWEETs and their bacterial homo-logues, SemiSWEETs, are related to the PQ-loop family, characterized by highly conserved pro-line and glutamine residues (PQ-loop motif) [ 41 ]. The PQ-loop family exhibits diverse activities; they function as cargo receptors in vesicle transport, mediate movement of basic amino acids across lysosomal membranes, and are also involved in phospholipase flippase function [ 42 – 44 ]. As yet, there are no reports of sugar transporters in viruses.…”