Probable metal transporter. Probably acts redundantly with the other metal transport proteins cnnm-1, cnnm-2, cnnm-3 and cnnm-5 to regulate Mg(2+) homeostasis. No visible phenotype. Quintuple knockout with cnnm-1, cnnm-2, cnnm-3 and cnnm-5 results in a reduced lifespan and 100% sterility. Belongs to the ACDP family.