Disclosed herein are methods of chemical conjugation comprising contacting a lysosomal enzyme with a first crosslinking agent to introduce aldehyde groups； contacting a lysosomal targeting peptide with a second crosslinking agent to introduce a hydrazide group at the N-terminal residue； contacting the lysosomal enzyme with aldehyde groups of step a. with the lysosomal targeting peptide with a hydrazide group at the N-terminal residue of step b； and forming a lysosomal enzyme-lysosomal targeting peptide conjugate.
