Receptor selectivity between the G proteins Gα₁₂ and Gα₁₃ is defined by a single leucine-to-isoleucine variation

Despite recent advances in structural definition of GPCR-G protein complexes, the basis of receptor selectivity between G proteins remains unclear. The Gα₁₂ and Gα₁₃ subtypes together form the least studied group of heterotrimeric G proteins. G protein-coupled receptor 35 (GPR35) has been suggested to couple efficiently to Gα₁₃ but weakly to Gα₁₂. Using combinations of cells genome-edited to not express G proteins and bioluminescence resonance energy transfer-based sensors, we confirmed marked selectivity of GPR35 for Gα₁₃. Incorporating Gα₁₂/Gα₁₃ chimeras and individual residue swap mutations into these sensors defined that selectivity between Gα₁₃ and Gα₁₂ was imbued largely by a single leucine-to-isoleucine variation at position G.H5.23. Indeed, leucine could not be substituted by other amino acids in Gα₁₃ without almost complete loss of GPR35 coupling. The critical importance of leucine at G.H5.23 for GPR35-G protein interaction was further demonstrated by introduction of this leucine into Gα_q, resulting in the gain of coupling to GPR35. These studies demonstrate that Gα₁₃ is markedly the most effective G protein for interaction with GPR35 and that selection between Gα₁₃ and Gα₁₂ is dictated largely by a single conservative amino acid variation.-Mackenzie, A. E., Quon, T., Lin, L.-C., Hauser, A. S., Jenkins, L., Inoue, A., Tobin, A. B., Gloriam, D. E., Hudson, B. D., Milligan, G. Receptor selectivity between the G proteins Gα₁₂ and Gα₁₃ is defined by a single leucine-to-isoleucine variation.