Novel synthetic biological study on intracellular distribution of human GlcNAc-1-phosphotransferase expressed in insect cells.

The article focuses on the expression, maturation, and intracellular localization of human mannose 6-phosphate (M6P)-modifying enzymes, particularly the GlcNAc-1-phosphotransferase α/β subunit (GNPTAB), in insect Sf9 cells compared to mammalian cells. It reports that while many lysosomal enzymes in mammals acquire M6P residues through a two-step Golgi process involving GNPTAB and NAGPA, insect cells lack M6P addition and transport lysosomal enzymes via an M6P-independent pathway. The study found that in Sf9 cells, GNPTAB predominantly localizes to the endoplasmic reticulum with minimal maturation, unlike its cis-Golgi localization and maturation in mammalian cells; however, co-expression of human site-1 protease (S1P) in Sf9 cells significantly enhanced GNPTAB maturation and cis-Golgi localization. These findings suggest that the intracellular distribution and processing of human GNPTAB in insect cells are regulated differently, providing insights into the limitations and potential modifications needed for functional expression of human M6P-modifying enzymes in insect cell systems.