Figure 6.

Model. (A) Crystal structures of activated Gα_i (PDB file 1GFI, top panel, overview; bottom panel, Switch II region enlarged, nucleotide shown in spacefill) demonstrate that the Trp π electrons are within 6 Å from the positively charged Arg in the Switch II helix. (B) Ordered regions of Gα_iGDP (PDB file 1BOF) shown in blue, Switch II region of Gα_tGDP in purple (from structural alignment of PDB file 1TAG and 1BOF), and nucleotide shown in spacefill. Top, overview; bottom panel, enlarged, depicting spatial separation of 8 Å or more between the Switch II Arg and Trp after GTP hydrolysis has occurred.