title: Developmental regulation of processing alpha-mannosidases and "intersecting" N-acetylglucosaminyltransferase in Dictyostelium discoideum.
abstract: We have identified three developmentally regulated oligosaccharide-processing enzyme activities in Dictyostelium discoideum. Two different alpha-mannosidase activities present at extremely low levels in vegetative cells are expressed during development. The first of these activities (MI) rises sharply from 6 to 12 h of development whereas the second activity (MII) rises sharply from 12 to 18 h of development. MI acts on Man9GlcNAc, which it can degrade to Man5GlcNAc but is inactive toward p-nitrophenyl-alpha-D-mannoside (pnpMan). MII acts on pnpMan but not Man9GlcNAc. These activities are distinct from each other and from lysosomal alpha-mannosidase activity as demonstrated by pH optima, substrate specificity, sensitivity to inhibitors and divalent cations, developmental profiles, and solubility. The characteristics of these developmentally regulated alpha-mannosidase activities are similar to those of Golgi alpha-mannosidases I and II from higher eucaryotes, and they appear to catalyze the in vivo formation of processed asparagine-linked oligosaccharides by developed cells. In addition, developed cells have very low levels of a soluble alpha-mannosidase activity, which is the predominant activity in vegetative cells. This soluble vegetative alpha-mannosidase activity has properties that are reminiscent of the endoplasmic reticulum alpha-mannosidase from rat liver. The intersecting N-acetylglucosaminyltransferase activity that we have described recently in vegetative cells of D. discoideum (Sharkey, D. J., and Kornfeld, R. (1989) J. Biol. Chem. 264, 10411-10419) has a developmental profile that is distinct from that of either of the alpha-mannosidase activities. It has maximum activity at 6 h of development and decreases sharply to its minimum level by 12 h of development. The changes that occur in the levels of these three processing enzymes with development correlate well with the different arrays of asparagine-linked oligosaccharides found in early and late stages of development (Sharkey, D. J., and Kornfeld, R. (1991) J. Biol. Chem. 266, 18485-18497).
authors.affiliation: Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: D J
authors.initials: DJ
authors.lastname: Sharkey
authors.forename: R
authors.initials: R
authors.lastname: Kornfeld
mesh_terms: D000818:Animals; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000201:enzymology; D004023:Dictyostelium / Q000201:enzymology* / Q000254:growth & development; D005964:Glucosyltransferases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008361:Mannosidases / Q000378:metabolism*; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases; D011499:Protein Processing, Post-Translational; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C037649:N-acetyllactosaminide beta-1,6-N-acetylglucosaminyltransferase; D008361:Mannosidases