Figure 2.

Structures of small GTPases. G boxes in the G domain (amino acids 1–166) are highlighted with orange boxes. The hypervariable (HVR) region, including a polybasic region (PBR) and a CAAX motif (166–189), is also highlighted. The CAAX box is the location in which post-translational modifications occur. The G domain consists of a six-stranded β-sheet and five α-helices, and has conserved sequence motifs G1 to G5. The G1 motif is also called the P-loop and is found in many nucleotide binding proteins, where it recognizes the β-phosphate and a Mg2⁺ ion of target nucleotides. The G2 motif (Switch 1) (Thr) makes contact with the γ-phosphate and the Mg²⁺ ion. The G3 motif (Switch 2) is responsible for GTP hydrolysis. The G4 and G5 motifs make specific contact with the guanine base to distinguish guanine from other nucleotides, Toma-Fukai et al., 2019 [46].