Anion/Sugar Transporter (AST)

The SLC17A5 gene encodes a vesicular excitatory amino acid transporter (VEAT) with dual physiologic functions. When present in synaptic vesicles in the central nervous system, sialin is responsible for vesicular storage and subsequent exocytosis of aspartate and glutamate. When present in lysosomes, it acts as an H(+)-coupled sialic acid exporter.

The isolated sequence encoded a predicted 495-residue protein with homology to members of the anion/cation symporter (ACS) family of transporters. This family contains eukaryotic inorganic anion transporters (such as Na+/phosphate cotransporters) as well as prokaryotic organic anion transporters (including H+/acid sugar symporters for hexuronate and glucarate).