Although the environment presents a smorgasbord of essential-to-life nutrients, it is the ability to select specific nutrients for import that enables most living organisms to thrive. One family of membrane-embedded proteins that accomplish nutrient import are ATP-independent periplasmic (TRAP) transporters, commonly found throughout bacteria and archaea. This family is known for the selective transport of carboxylate, phosphate and sulfonate-containing nutrients and are the only known secondary transporters (not requiring ATP) that are dependent on an auxiliary substrate-binding protein. This substrate-binding protein “P” is located free in the periplasm (or tethered to the outer membrane) and sequesters the substrate before delivering it to the membrane-bound components, “Q” and “M”, for transport into the cell. Recent studies have elucidated the structure of the membrane embedded components of the transporter family, shedding light on the import mechanism. However, questions remain about how the substrate-binding protein interacts with the membrane components to form the full transport cycle.
I am investigating a TRAP transporter from Oleidesulfovibrio alaskensis, known to import isethionate. High resolution crystal structures of the “P” substrate binding protein have been determined, allowing the binding of isethionate to be characterised in combination with complementary biophysical data. Nanobodies have been generated to aid structural studies of the “Q and M” membrane components using cryo-EM. These are the first steps towards deciphering how the components of TRAP transporters interact, to transport essential nutrients across the cytoplasmic membrane. This work will help underpin the future development of new antibiotics to combat pathogenic bacteria.