A method of making a modified lysosomal targeting peptide, comprising: a. contacting variant insulin-like growth factor 2 (vIGF2) with a bifunctional crosslinking agent to introduce a protected hydrazide group at the N-terminal residue; b. deprotecting the hydrazide-modified vlGF2 in solution to form a deprotected hydrazide-modified vIGF2; c. contacting a lysosomal enzyme with a first crosslinking agent to introduce aldehyde groups; d. linking at least one deprotected hydrazide modified vlGF2 to the lysosomal enzyme; wherein: the vlGF2 comprises one or more of the following changes compared to the wild type human IGF2 sequence: deletion of N-terminal amino acid residues 1-4; glutamic acid residue at position 6 of wildtype human IGF2 substituted with arginine; tyrosine residue of wildtype human IGF 2 at position 27 substituted with leucine; lysine residue at position 65 of human IGF-2 substituted with arginine; the bifunctional crosslinking agent comprises acetone-, dimethylbenzyloxycarbonyl-, trimethylbenzyloxycarbonyl- protected hydrazide groups, or any combination thereof; or the bifunctional crosslinking agent comprises N-tert-butoxycarbonyl (tBoc)-protected hydrazide crosslinker (NHS-PEG4-tBoc-hydrazide), methoxybenzyloxy carbonyl -protected hydrazide (NHS-PEG4-BOM-hydrazide), acetone-protected NHS-PEG 4 -hydrazide, dimethylbenzylcarbonyl-protected NHS-PEG 4 -hydrazide, trimethylbenzyloxycarbonyl-protected NHS-PEG 4 -hydrazide; or a cross linker of formula: or any combination thereof. a. contacting variant insulin-like growth factor 2 (vIGF2) with a bifunctional crosslinking agent to introduce a protected hydrazide group at the N-terminal residue; b. deprotecting the hydrazide-modified vlGF2 in solution to form a deprotected hydrazide-modified vIGF2; c. contacting a lysosomal enzyme with a first crosslinking agent to introduce aldehyde groups; d. linking at least one deprotected hydrazide modified vlGF2 to the lysosomal enzyme; the vlGF2 comprises one or more of the following changes compared to the wild type human IGF2 sequence: deletion of N-terminal amino acid residues 1-4; glutamic acid residue at position 6 of wildtype human IGF2 substituted with arginine; tyrosine residue of wildtype human IGF 2 at position 27 substituted with leucine; lysine residue at position 65 of human IGF-2 substituted with arginine; deletion of N-terminal amino acid residues 1-4; glutamic acid residue at position 6 of wildtype human IGF2 substituted with arginine; tyrosine residue of wildtype human IGF 2 at position 27 substituted with leucine; lysine residue at position 65 of human IGF-2 substituted with arginine; the bifunctional crosslinking agent comprises acetone-, dimethylbenzyloxycarbonyl-, trimethylbenzyloxycarbonyl- protected hydrazide groups, or any combination thereof; or the bifunctional crosslinking agent comprises N-tert-butoxycarbonyl (tBoc)-protected hydrazide crosslinker (NHS-PEG4-tBoc-hydrazide), methoxybenzyloxy carbonyl -protected hydrazide (NHS-PEG4-BOM-hydrazide), acetone-protected NHS-PEG 4 -hydrazide, dimethylbenzylcarbonyl-protected NHS-PEG 4 -hydrazide, trimethylbenzyloxycarbonyl-protected NHS-PEG 4 -hydrazide; or a cross linker of formula: or any combination thereof.