title: SUMOylation of pancreatic glucokinase regulates its cellular stability and activity.
abstract: Glucokinase is the predominant hexokinase expressed in hepatocytes and pancreatic β-cells, with a pivotal role in regulating glucose-stimulated insulin secretion, illustrated by glucokinase gene mutations causing monogenic diabetes and congenital hyperinsulinemic hypoglycemia. A complex tissue-specific network of mechanisms regulates this enzyme, and a major unanswered question in glucokinase biology is how post-translational modifications control the function of the enzyme. Here, we show that the pancreatic isoform of human glucokinase is SUMOylated in vitro, using recombinant enzymes, and in insulin-secreting model cells. Three N-terminal lysines unique for the pancreatic isoform (Lys-12/Lys-13 and/or Lys-15) may represent one SUMOylation site, with an additional site (Lys-346) common for the pancreatic and the liver isoform. SUMO-1 and E2 overexpression stabilized preferentially the wild-type human pancreatic enzyme in MIN6 β-cells, and SUMOylation increased the catalytic activity of recombinant human glucokinase in vitro and also of glucokinase in target cells. Small ubiquitin-like modifier conjugation represents a novel form of post-translational modification of the enzyme, and it may have an important regulatory function in pancreatic β-cells.
authors.affiliation: KG Jebsen Center for Diabetes Research, Department of Clinical Medicine, N-5020 Bergen, Norway.
authors.forename: Ingvild
authors.initials: I
authors.lastname: Aukrust
authors.forename: Lise
authors.initials: L
authors.lastname: Bjørkhaug
authors.forename: Maria
authors.initials: M
authors.lastname: Negahdar
authors.forename: Janne
authors.initials: J
authors.lastname: Molnes
authors.forename: Bente B
authors.initials: BB
authors.lastname: Johansson
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Müller
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Haas
authors.forename: Steven P
authors.initials: SP
authors.lastname: Gygi
authors.forename: Oddmund
authors.initials: O
authors.lastname: Søvik
authors.forename: Torgeir
authors.initials: T
authors.lastname: Flatmark
authors.forename: Rohit N
authors.initials: RN
authors.lastname: Kulkarni
authors.forename: Pål R
authors.initials: PR
authors.lastname: Njølstad
mesh_terms: D000818:Animals; D002241:Carbohydrates / Q000737:chemistry; D002384:Catalysis; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic; D005941:Glucokinase / Q000737:chemistry*; D050417:Insulin-Secreting Cells / Q000166:cytology; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D013058:Mass Spectrometry / Q000379:methods; D051379:Mice; D009154:Mutation; D010179:Pancreas / Q000201:enzymology*; D020033:Protein Isoforms; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000737:chemistry; D058207:Sumoylation
chemical_list: D002241:Carbohydrates; D020033:Protein Isoforms; D011994:Recombinant Proteins; D005941:Glucokinase