title: GCK-MODY diabetes associated with protein misfolding, cellular self-association and degradation.
abstract: GCK-MODY, dominantly inherited mild fasting hyperglycemia, has been associated with >600 different mutations in the glucokinase (GK)-encoding gene (GCK). When expressed as recombinant pancreatic proteins, some mutations result in enzymes with normal/near-normal catalytic properties. The molecular mechanism(s) of GCK-MODY due to these mutations has remained elusive. Here, we aimed to explore the molecular mechanisms for two such catalytically 'normal' GCK mutations (S263P and G264S) in the F260-L270 loop of GK. When stably overexpressed in HEK293 cells and MIN6 β-cells, the S263P- and G264S-encoded mutations generated misfolded proteins with an increased rate of degradation (S263P>G264S) by the protein quality control machinery, and a propensity to self-associate (G264S>S263P) and form dimers (SDS resistant) and aggregates (partly Triton X-100 insoluble), as determined by pulse-chase experiments and subcellular fractionation. Thus, the GCK-MODY mutations S263P and G264S lead to protein misfolding causing destabilization, cellular dimerization/aggregation and enhanced rate of degradation. In silico predicted conformational changes of the F260-L270 loop structure are considered to mediate the dimerization of both mutant proteins by a domain swapping mechanism. Thus, similar properties may represent the molecular mechanisms for additional unexplained GCK-MODY mutations, and may also contribute to the disease mechanism in other previously characterized GCK-MODY inactivating mutations.
authors: Department of Clinical Medicine, University of Bergen, N-5020 Bergen, Norway.
authors: Maria
authors: M
authors: Negahdar
authors: Ingvild
authors: I
authors: Aukrust
authors: Bente B
authors: BB
authors: Johansson
authors: Janne
authors: J
authors: Molnes
authors: Anders
authors: A
authors: Molven
authors: Franz M
authors: FM
authors: Matschinsky
authors: Oddmund
authors: O
authors: Søvik
authors: Rohit N
authors: RN
authors: Kulkarni
authors: Torgeir
authors: T
authors: Flatmark
authors: Pål Rasmus
authors: PR
authors: Njølstad
authors: Lise
authors: L
authors: Bjørkhaug
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000235:genetics* / Q000378:metabolism; D005941:Glucokinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D017830:Octoxynol; D011487:Protein Conformation; D017510:Protein Folding; D055503:Protein Multimerization; D059748:Proteolysis; D057165:Proteostasis Deficiencies / Q000235:genetics / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism
chemical_list: D050505:Mutant Proteins; D017830:Octoxynol; D005941:Glucokinase