Probable metal transporter. The interaction with the metal ion chaperone COX11 suggests that it may play a role in sensory neuron functions (By similarity). May play a role in biomineralization and retinal function. {ECO:0000250, ECO:0000269|PubMed:19200525, ECO:0000269|PubMed:19200527}. This is the function of CNNM4 (cyclin and CBS domain divalent metal cation transport mediator 4, Ensembl gene identifier ENSG00000158158).