Abstract
When cells are starved of their substrate, many nutrient transporters are induced. These undergo rapid endocytosis and redirection of their intracellular trafficking when their substrate becomes available again. The discovery that some of these transporters also act as receptors, or transceptors, suggests that at least part of the sophisticated controls governing the trafficking of these proteins has to do with their signaling function rather than with control of transport. In yeast, the general amino acid permease Gap1 mediates signaling to the protein kinase A pathway. Its endocytic internalization and intracellular trafficking are subject to amino acid control. Other nutrient transceptors controlling this signal transduction pathway appear to be subject to similar trafficking regulation. Transporters with complex regulatory control have also been suggested to function as transceptors in other organisms. Hence, precise regulation of intracellular trafficking in nutrient transporters may be related to the need for tight control of nutrient-induced signaling.
Highlights
Extracellular nutrients can trigger induction of transporters and enzymes required for their uptake and metabolism
Recent work has shown that of the six Gap1 homologs in C. albicans, three can function as transceptors for rapid amino acid activation of the protein kinase A (PKA) pathway when expressed in S. cerevisiae [27]
Determination of PKAdependent phenotypes in stationary-phase cells of strains expressing alleles of nutrient transporters that constitutively reside in the plasma membrane may reveal whether they might have the capacity to signal to the PKA pathway
Summary
Extracellular nutrients can trigger induction of transporters and enzymes required for their uptake and metabolism. Recent work has identified amino acid analogs that are not transported but are still able to trigger signaling and cause Gap1 to function as a true receptor protein [17]. Recent work has shown that of the six Gap1 homologs in C. albicans, three can function as transceptors for rapid amino acid activation of the PKA pathway when expressed in S. cerevisiae [27].
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