Structural and computational study of cationic amino acid transporters (360G-Wellcome-203741_Z_16_A)

Cells are surrounded by a lipid membrane, which isolates the cell content from the extracellular solution. The hydrophobic core of the membrane is impermeable to many hydrophilic substances including amino acids. To circumvent this problem, cells use transporters that can translocate amino acids across the membrane. This translocation process can sometimes be proton-coupled, but in some cases, certain transporters appear to function without the need for proton coupling. The reasons why some transporters are proton-coupled while others are not and how the proton coupling works, remain elusive. Humans contain two closely related types of amino acid transporter, the cationic amino acid transporters (CATs), which are proton independent and the proton-coupled amino acid transporters (PATs), which use protons for transport. Recent work in the Newstead laboratory has characterized a bacterial homolog of CATs that is proton-dependent, which was surprising. My DPhil project is trying to understand the mechanism of proton coupling in these transporters using a comparative approach between these two example proteins. Comparison of residues at key locations provides a working hypothesis of which residues may give rise to proton dependence. We will investigate this via the use of biochemical and cell-based transport assays, X-ray crystallography and molecular dynamics simulations.