Constitutive activity of Gs alpha is associated with several human diseases, including McCune‐Albright Syndrome (MAS). In this genetic disorder, Arg201 is mutated to His, Cys, or Ser, resulting in inhibition of GTP hydrolysis and subsequent overactivation of adenylyl cyclase and elevated basal cAMP levels. Previous studies identified three intragenic suppressor sites that blocked the constitutive activity caused by R201H: F142, R231, and L266. These mutations did not by themselves alter the activity of Gs alpha. The intragenic suppressors were examined for their ability to block the other MAS alleles. F142S and R231C suppressed the constitutive activity of both of MAS alleles. L266N suppressed R201S, and is currently being tested for the ability to block the constitutive activity of R201C. Thus, the intragenic suppressors may be useful drug targeting sites for MAS mutations generally, not just for R201H‐caused cases of the disease. Grant Funding Source: Supported by NIH grant 1R15ED020190‐01

McCune‐Albright Syndrome (MAS) is a genetic disorder caused by a mutation in Gs alpha at Arg201 that inhibits GTP hydrolysis, constitutively activating the protein. We identified three sites that, when mutated, suppressed the constitutive activity caused by R201H: F142, R231, and L266. None of the three mutations by themselves caused constitutive activity of the protein or significantly changed cellular responsiveness to hormone, as measured by the ability of a luteinizing hormone receptor agonist to activate cAMP production. We have now examined the ability of mutations at these three sites to suppress other activating mutations of Gs alpha. Other McCune‐Albright associated mutations include R201C and R201S. Both F142S and R231C were able to suppress the constitutive activity of both of previously untested R201 substitutions. L266N was able to suppress R201S, and experiments investigating its effects on R201C are ongoing. Gs alpha can also be constitutively activated by the Q227L substitution, associated with a variety of adenomas. The mutations identified as suppressors of R201H were all unable to suppress the constitutive activity of Q227L, suggesting that the action of the suppressors is specific to the R201 site and not generalizable to other activating perturbations of Gs alpha. Grant Funding Source: Supported by NIH grant 1R15ED020190‐01