Fig. 5

Role of the N-terminal helix (α_N) in the Gα_q-PLCβ3 complex. a The model of Gα_q (light orange) is shown as a space filling structure and contains the α_N-helix and other regions as indicated. PLCβ3 (yellow) is depicted as a cartoon ribbon, containing the helix-turn-helix segment (Hα1/Hα2), the N-terminal PH domain, four EF hands, the catalytic TIM barrel, and a C2 domain. PLCβ3-interacting residues of Gα_q are colored in magenta. The carboxy-terminal (CT) domain of PLCβ3 is not included in the structural model. The structure of the α_N-helix is generated by replacing the amino acid sequence of Gα_i (Gα_iβ₁γ₂, PDB code: 1GP2) with the Gα_q sequence. The final model is generated by alignment of Gα_q-PLCβ3 (PDB code: 3OHM) and the modified heterotrimer Gα_qβ₁γ₂ using PyMOL (The PyMOL Molecular Graphics System, Version 1.3 Schrödinger, LLC). The orientation of the α_N-helix represents the conformation in the heterotrimer and is not optimized for the Gα_q-PLCβ3 complex. In this case, the α_N-helix points towards the cell membrane and clashes with PLCβ3, but in fact may exist in a conformation which interacts with PLCβ3. b Schematic representation of 14αΝ and zαN chimeras. c Cells were co-transfected with PLCβ2 and Gα protein or the indicated chimeras. Co-immunoprecipitation assays were performed and analyzed as in Fig. 2. Data shown represent one of three sets of immunoblots; two other sets yielded similar results. For the IP₃ accumulation assay, HEK293 cells were transiently transfected with the wild-type or constitutively active mutants (QL) of Gα proteins or chimeras and analyzed as in Fig. 2. *, IP₃ production was significantly enhanced as compared to corresponding wild-type transfected cells; Dunnett t test, p < 0.05