Described herein are methods of making targeting peptides conjugated to recombinant lysosomal enzymes by modifying the amino (N)-terminus and one or more lysine residues on recombinant human lysosomal enzymes using a first crosslinking agent to give rise to first crosslinking agent modified recombinant human lysosomal enzymes, modifying the first amino acid within a short linker at the amino (N)-terminus on a variant IGF-2 peptide using a second crosslinking agent to give rise to a second crosslinking agent modified variant IGF-2 peptide, and then conjugating the first crosslinking agent modified recombinant human lysosomal enzyme to the second crosslinking agent modified variant IGF-2 peptide containing a short linker. Also described herein are conjugates synthesized characterized as having higher affinities for the IGF2/CI-MPR receptor and cellular uptake using the methods disclosed herein. Also described herein are treatment methods using the disclosed conjugates.
