Sul1 and Sul2 sulfate transceptors signal to protein kinase A upon exit of sulfur starvation.
Bottom Line: Overall, our data suggest that transceptors can undergo independent conformational changes, each responsible for triggering different downstream processes.The Sul1 and Sul2 transceptors are the first identified plasma membrane sensors for extracellular sulfate.High affinity transporters induced upon starvation for their substrate may generally act as transceptors during exit from starvation.
Affiliation: From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and.Show MeSH
Related in: MedlinePlus
Mentions: Previous work has shown that sulfate addition to sulfur-starved cells on a glucose-containing medium triggers activation of trehalase, a classical read-out for rapid PKA activation in vivo in yeast (27). We now show that this sulfate-induced activation of PKA requires one of the two sulfate transporters, either Sul1 or Sul2 (Fig. 1A). Using site- and phospho-specific antibodies, we show that activation of trehalase is correlated with phosphorylation on the PKA consensus site, Ser-21 (Fig. 1B), similar to trehalase activation by glucose and nitrogen sources in appropriately starved cells (28). We next confirmed the requirement of Sul1 or Sul2 for sulfate-induced activation of PKA using several other in vivo read-outs for activation of the PKA pathway. After the addition of sulfate to sulfur-starved cells, the carbohydrates trehalose (Fig. 1C) and glycogen (Fig. 1D) were mobilized, heat stress tolerance dropped (Fig. 1E), expression of the heat shock gene HSP12 was down-regulated (Fig. 1F), and expression of the ribosomal gene RPL25 was up-regulated (Fig. 1G). All of these sulfate-induced processes required the presence of either Sul1 or Sul2 (Fig. 1, A–G). Consistent with previous results (27), sulfate activation of the PKA targets in sulfur-starved cells with BY genetic background was not associated with an increase in the cAMP level (Fig. 1H). In the sul1Δ sul2Δ strain, there was a residual phosphorylation signal for trehalase (Fig. 1B) that correlated with a residual increase in its activity (Fig. 1A). Also for the other PKA targets, trehalose mobilization (Fig. 1C), glycogen mobilization (Fig. 1D), loss of heat stress tolerance (Fig. 1E), reduced expression of HSP12 (Fig. 1F), and enhanced expression of RPL25 (Fig. 1G), there was a residual effect in the sul1Δ sul2Δ strain. This residual effect is probably due to uptake of sulfate through a third sulfate carrier with much lower affinity for sulfate than Sul1 and Sul2 because the sul1Δ sul2Δ strain can grow with a very high sulfate concentration (>20 mm) as the sole source of sulfur in the medium.2
Affiliation: From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and.