A Family of Yeast Proteins Mediating Bidirectional Vacuolar Amino Acid Transport

Abstract

Seven genes in Saccharomyces cerevisiae are predicted to code for membrane-spanning proteins (designated AVT1-7) that are related to the neuronal ␥-aminobutyric acid-glycine vesicular transporters. We have now demonstrated that four of these proteins mediate amino acid transport in vacuoles. One protein, AVT1, is required for the vacuolar uptake of large neutral amino acids including tyrosine, glutamine, asparagine, isoleucine, and leucine. Three proteins, AVT3, AVT4, and AVT6, are involved in amino acid efflux from the vacuole and, as such, are the first to be shown directly to transport compounds from the lumen of an acidic intracellular organelle. This function is consistent with the role of the vacuole in protein degradation, whereby accumulated amino acids are exported to the cytosol. Protein AVT6 is responsible for the efflux of aspartate and glutamate, an activity that would account for their exclusion from vacuoles in vivo. Transport by AVT1 and AVT6 requires ATP for function and is abolished in the presence of nigericin, indicating that the same pH gradient can drive amino acid transport in opposing directions. Efflux of tyrosine and other large neutral amino acids by the two closely related proteins, AVT3 and AVT4, is similar in terms of substrate specificity to transport system h described in mammalian lysosomes and melanosomes. These findings suggest that yeast AVT transporter function has been conserved to control amino acid flux in vacuolar-like organelles.Caenorhabditis elegans UNC-47 (1) and the vertebrate homologues from rat (VGAT, 1) and mouse (VIAAT, 2) are synaptic vesicular transporters that are expressed exclusively in inhibitory neurons (see also Ref. 3) and are specific for the neurotransmitters ␥-aminobutyric acid (GABA) 1 and glycine. These proteins differ in sequence, structure, and bioenergetics from the previously characterized family of vesicular transporters that package monoamines and acetylcholine (for current reviews, see Refs. 4 and 5). Common to all of these transporters is the fact that the movement of substrate from the cytosol into synaptic vesicles is driven by a proton electrochemical gradient that is generated by the action of a vacuolar-type H ϩ -ATPase and involves the exchange of lumenal protons.A search for other vertebrate proteins related to the GABAglycine vesicular transporters has led recently to the isolation and expression of cDNAs that, surprisingly, code for Na ϩ

Genome-wide coexpression dynamics: Theory and application

“…From the list of LAPs for YNL101W (Table 8, which is published as supporting information on the PNAS web site), we find several genes involved in autophagy, protein degradation, and transport: AUT7 (essential for autophagy, appearing six times), PRE6 and PUP1 (20S proteasome subunits), RPT6 (26S proteasomeregulatory subunit), CLC1 (clathrin light chain), YPT52 (GTPbinding protein of the RAB family), and UBP2 (ubiquitinspecific proteinase). This seems consistent with the newly identified role of YNL101W (newly named AVT4) as a membrane transporter responsible for the efflux of tyrosine and other large neutral amino acids from the vacuole (25).…”

The plant hormone indoleacetic acid induces invasive growth in Saccharomyces cerevisiae

“…Arabidopsis orthologs of the Avt proteins have been shown to transport amino acids when expressed in S. cerevisiae (18). Previous studies in yeast have implicated some of the Avt proteins in the vacuolar transport of amino acids (16), but neither our analysis nor recent studies on the global protein localization (20) give evidence for vacuolar localization of the Avt proteins. Moreover, none of the amino acids thought to be transported by Avt proteins, can reverse the inhibition of IAA suggesting that these proteins are unlikely to transport amino acids across the plasma membrane.…”

“…These proteins and other members of the larger AAAP family transport very diverse compounds such as amino acids and ␥-aminobutyric acid (16,19). Some of the Arabidopsis AAAP proteins appear to have a broad spectrum, capable of transporting several different amino acids (17,18).…”

Identification of the fnx1+ and fnx2+ genes for vacuolar amino acid transporters in Schizosaccharomyces pombe

“…Recently two gene families, AVT and vacuolar transporter for basic amino acids (VBA), were found to be involved in amino acid transport in the S. cerevisiae vacuole [7,8]. In the AVT family, AVT1 is involved in uptake of neutral amino acids, and AVT3 and AVT4 in the extrusion of these amino acids from vacuoles [7]. All the members of the VBA family, VBA1, VBA2 and VBA3, are involved in the uptake of basic amino acids into vacuoles [8].…”