Compositions comprising a modified GIcNAc-1-phosphotransferase and methods of use thereof

A method to increase binding of a protein of interest to cell surface mannose 6-phosphate receptor (Man-6-P), the method comprising expressing a modified GlcNAc-1-PT α/β subunit in a cell, wherein the modified GlcNAc-1-PT α/β subunit comprises an internal deletion of amino acids with reference to full-length human GlnNAc-1-PT α/β subunit having the sequence of SEQ ID NO:1, wherein amino acids 86 to 322 and amino acids 438 to 928 are deleted, and wherein the increased binding of a protein of interest to cell surface mannose 6-phosphate receptor (Man-6-P) is compared to the binding of a protein of interest to cell surface mannose 6-phosphate receptor (Man-6-P) in a cell expressing endogenous GlcNAc-1-PT α/β subunit.