RhtX from Sinorhizobium meliloti 2011 and FptX from Pseudomonas aeruginosa appear to be single polypeptide transporters, from the major facilitator family (see pfam07690) for import of siderophores as a means to import iron. This function was suggested by proximity to siderophore biosynthesis genes and then confirmed by study of knockout and heterologous expression phenotypes. [Transport and binding proteins, Cations and iron carrying compounds]
Jiyao W et al.(2023). "The conserved domain database in 2023.",