Fig. 3.

COG0523 structural models. (A) ‘Elephant’ representation of COG0523 metallochaperones with G-loops and nucleotide binding and hydrolysis motifs highlighted.¹ The variable C-terminal domain is thought to harbor sequence-specific determinants for specific interactions with a client protein(s). (B) The only metal-bound COG0523 structure, of E. coli YjiA (PDB: 4ixm). The GTPase and C-terminal domains are indicated and the G-loops are shaded as in panel A. The coordination structure of the high affinity, regulatory Zn^II site is shown, proposed to involve E37, E42, and C66; the side chain of E39, also highlighted, appears to point away from the metal, but could not be modeled past Cβ.²⁹ This side chain also points away from the metal binding cleft in the apo-YjiA structure.⁶³ This metal site localizes to the G2 loop and the β-meander⁶³ (shaded gold) defines an insertion in a canonical G3E P-loop GTPase fold (right). (C) Ribbon structures of Helicobacter pylori HypB (4lps)²⁴ and H. pylori UreG (4hi0)¹¹² dimers (one subunit shaded gray, the other white) with the G-loops in the gray protomer shaded as in panels A and B in the same orientation as EcYjiA, (panel B, right). GTP analog is shown in black stick. (D) Structure of Tetrahymena Shulin C1 domain illustrating structural similarity to G3E P-loop GTPases;⁸¹ however, sequence similarity to EcYjiA is undetectable. (E) Ribbon representation of the vertebrate Cdc42-DOCK8 complex (3vh1), with Cdc42 shaded gray and G-loops colored as above, and DOCK8, a Cdc42-specific guanine nucleotide exchange factor, (GEF) shaded gold.⁶⁵