Energy-coupling factor (ECF) transporters form a new family of ATP-binding cassette (ABC) transporters and are widely used by prokaryotes to take up micronutrients from the environment. Instead of using the periplasmic solute-binding proteins (SBPs), ECF transporters use the membrane S proteins for substrate capture and translocation. In this review, we will focus on structural advances that have been made regarding how substrates are recognized by ECF transporters and possible transport mechanisms employed by the ECF transporters.
