Involved in mercury resistance (PubMed:3038684). Acts as a mercury scavenger that specifically binds to a mercuric ion in the periplasm and probably passes it to the cytoplasmic mercuric reductase MerA via the mercuric transport protein MerT (Probable). Monomer. Merp-merT deletion mutant is unable to transport mercury into the cytoplasm and shows almost complete loss of the resistance phenotype. Belongs to the MerP family.