Expression, purification and characterization of a Drosophila melanogaster Mannosidase orthologous to Drosophila melanogaster Golgi Mannosidase II

Abstract

Drosophila melanogaster Golgi Mannosidase IIb (dGMIIb) is a class II (CAZy GH38) α-mannosidase involved in the processing of N-glycan structures in the insect secretory pathway. The enzyme activity of this 140-145 kDa protein is stimulated by cobalt, sensitive to furanose inhibitor mimics (swainsonine and 1,4-di-deoxy-mannitol), and has a pH optimum of 6.0. dGMIIb is an ortholog of the well-characterized Drosophila melanogaster Golgi Mannosidase II (dGMII). The preferred natural substrate for dGMII is GlcNAcMan5GlcNAc2 asparagine (N)-linked proteins, whereas the preferred natural substrate for dGMIIb is Man5GlcNAc2. dGMII has been crystallized and its active site extensively studied as a potential target for inhibition in cancer therapeutics. Modeling of dGMIIb using the crystal structure of dGMII as a template reveals differences in the GlcNAc - binding “anchoring site” which may account for the distinct substrate specificities of these processing enzymes.