Different biochemical properties explain why two equivalent G? subunit mutants cause unrelated diseases.

ABSTRACT: There is an increasing number of disease-associated G? 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 (G?s) and other studies revealed gain-of-function G? 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 G?s-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to G?o-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to G?o-R243H, G?s-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 G?s (D173N) with a counterpart cancer mutation in G?o (D151N). G?o-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 G?o and severe for G?s). We conclude that G?s-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas G?o-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.

SUBMITTER: Leyme A 

PROVIDER: S-EPMC4139202 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature