title: Different biochemical properties explain why two equivalent Gα subunit mutants cause unrelated diseases.
abstract: There is an increasing number of disease-associated Gα mutations identified from genome-wide sequencing campaigns or targeted efforts. Albright's Hereditary Osteodystrophy (AHO) was the first inherited disease associated with loss-of-function mutations in a G protein (Gαs) and other studies revealed gain-of-function Gα mutations in cancer. Here we attempted to solve the apparent quandary posed by the fact that the same mutation in two different G proteins appeared associated with both AHO and cancer. We first confirmed the presence of an inherited Gαs-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to Gαo-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to Gαo-R243H, Gαs-R265H activity is compromised due to greatly impaired nucleotide binding in vitro and in cells. We obtained equivalent results when comparing another AHO mutation in Gαs (D173N) with a counterpart cancer mutation in Gαo (D151N). Gαo-R243H binds nucleotides efficiently under steady-state conditions but releases GDP much faster than the WT protein, suggesting diminished affinity for the nucleotide. These results indicate that the same disease-linked mutation in two different G proteins affects a common biochemical feature (nucleotide affinity) but to a different grade depending on the G protein (mild decrease for Gαo and severe for Gαs). We conclude that Gαs-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas Gαo-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Anthony
authors: A
authors: Leyme
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Arthur
authors: A
authors: Marivin
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Jason
authors: J
authors: Casler
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Lien T
authors: LT
authors: Nguyen
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118 mgm1@bu.edu.
authors: Mikel
authors: M
authors: Garcia-Marcos
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002864:Chromogranins; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009369:Neoplasms / Q000235:genetics* / Q000378:metabolism*; D010375:Pedigree; D021122:Protein Subunits; D011547:Pseudohypoparathyroidism / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein
chemical_list: D002864:Chromogranins; C584143:GNAO1 protein, human; D050505:Mutant Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D006160:Guanosine Triphosphate; C406732:GNAS protein, human; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs
keywords: Albright's Hereditary Osteodystrophy; Cancer; Enzyme Kinetics; G Protein-coupled receptor (GPCR); Heterotrimeric G Protein; Oncogene; Pseudohypoparathyroidism Ia