Mechanism of a membrane ‘transceptor’: A transporter and a receptor in one

Abstract

Certain transporter‐like membrane proteins also act as receptors for the availability of external nutrient content in eukaryotic cells, hence called ‘transceptors’. The concept came into the picture when several transporter‐like receptors were discovered in eukaryotes. They can be classified as transporting (example yeast Mep2, Gap1, Pho84, mammalian SNAT2) and non‐transporting (example yeast Snf3, Rgt2, mammalian SGLT3) transceptors based on their ability to transport the substrate. I sought to determine the mechanisms by which a key phosphate transceptor combines these dual functions at the level of atomic structure and biochemistry. Phosphate is an essential macronutrient for structural and metabolic requirements of all eukaryotic cells; for nucleotide and lipid biosynthesis, cell signaling by phosphorylation and energy storage (ATP), and because of its impact, pathways inside the cell must respond to availability even outside the cell, in a regulated fashion. I selected the phosphate transceptor PiPT from Piriformospora indica, for which structure is available in atomic details, the first for any transceptor. This enabled the mutagenesis of regions as a test of their transport and/or receptor function, and further structure analysis aimed at probing the signaling pathway across the membrane. Compounds known to inhibit transport and/or activate the receptor function were tested and used to distinguish between the two functions. Site‐directed mutagenesis based on the available structure was exploited to determine the role of residues that bind phosphate in the central transport site and to define the alternate access to both sides of the membrane, and the separate pathway for protons and the way their transport is absolutely coupled to phosphate transport. Transport assays and biochemical assays probing the intracellular signaling response for the mutants studied assisted in determination of a possible mechanism of transport and receptor function.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.