Part of the tripartite ATP-independent periplasmic (TRAP) transport system DctPQM involved in the uptake of isethionate (2-hydroxyethanesulfonate), which is then catabolized by enzymes encoded by adjacent genes in the locus. The DctP subunit is the solute-binding protein. Thereby is involved in an anaerobic respiration pathway that converts the sulfonate isethionate to ammonia, acetate and sulfide. 2-hydroxyethane-1-sulfonate(out) + Na(+)(out) = 2-hydroxyethane-1-sulfonate(in) + Na(+)(in) Organosulfur degradation; alkanesulfonate degradation. The complex comprises the periplasmic solute receptor protein DctP, and the fused transmembrane protein DctMQ. Highly up-regulated in the presence of isethionate. Cells lacking this gene lose the ability to grow with isethionate as the terminal electron acceptor. Belongs to the bacterial solute-binding protein 7 family.