Provided are fusion proteins between p97 (melanotransferrin) and iduronate-2-sulfatase (IDS), and related compositions and methods of use thereof, for instance, to facilitate delivery of IDS across the blood-brain barrier (BBB) and/or improve its tissue penetration in CNS and/or peripheral tissues, and thereby treat and/or diagnose Hunter Syndrome (Mucopolysaccharidosis type II; MPS II) and related lysosomal storage disorders, including those having a central nervous system (CNS) component.