Evolution of a Signaling Nexus Constrained by Protein Interfaces and Conformational States
Figure 7
G(io) class-distinctive sites in structural context.
(A) The structure of the GoLoco domain of RGS14 (blue cartoon) bound to an inactive Gαi1 (Gαi1• GDP) (PDB ID 1KJY). In all structural panels in this figure, Gαi1 is shown as spheres or cartoon with core residues colored gray if they are conserved between Gα subunits (either INV (invariant) or η (non-distinct) amino acids) while G(io)-distinctive sites are colored green only if they contain a ∂ (distinct) amino acid. Non-core residues and d sites are colored white. G(io)-distinctive sites are numbered according to their position in the signature sequence (see panel (D)). Panel A shows two views of Gαi1 related by a 180° rotation about the horizontal axis. The left view is of the switch region of Gαi1 while the right view is of the top of the subunit. (B) Closeup view of β-strand 6 and α-helix 5 from Gαi1 with the side chains of G(io)-distinctive residues in a stick rendering. The orientation is the same as the right-hand view in panel A. Helix 5 rotates and translates toward β-strand 6 (arrow) during GPCR-mediated activation of the Gα subunit. Sites 12 and 13 in Gαi1 are the ∂ residue but show subtype variation within the G(io) class. G(io) site 11 (colored lime green) lies in β-strand 6 and also shows subtype variation; Gαi1 possesses the η residue at that site and is, therefore, colored gray in (A). (C) Structure of Gαi1•GDP (sphere display) bound to Gβ•Gγ (deepblue/copper cartoon) heterodimer (PDB ID 1GP2). Two orientations related by a 180° rotation about the vertical axis are shown. (D) Signature sequences are formed by grouping all distinctive sites for a given class together, removing all residues between individual distinctive sites of the noted class. The distinctive sites for each class are presented in order from the N-terminus to the C-terminus and numbered accordingly. Amino acids that correspond to the ∂ values at the G(io) site are colored green. Sites in helix 5 that have been proposed to be important for coupling to the GPCR are denoted by ‘5’ above the site, while site 11 in strand 6 is denoted by ‘b’ above the site.