A. In silico model of MglA with GPPNHP in the predicted active site; B. MglA model without docked nucleotide. A three-dimensional representation of MglA was constructed with SWISS-MODEL using the crystal structure of Sar1p as a template [24–26] and the result is shown here as generated by PyMOL . All mutations made in MglA were between residues 18 and 145. In both panels, targeted residues are colored as follows: P-loop (PM1), yellow; PM3, green; D52/T54, red; G2 motif, purple; leucine rich repeat (LRR), orange. Thr78 corresponds to the conserved aspartate residue characteristic of the Ras-superfamily, and is located at the end of the α-helix shown in green. Side-chains are shown for residues that were targets of study through site-directed mutagenesis. A: A GTP analog was docked with MglA to identify residues in or near the active site that might directly interact with either the guanine base or the phosphates. B: The MglA apoenzyme is shown with residues indicated. G21 denotes the location of the PM1 region, the N114 residue shown is in the G2 motif. Both D52A and L124 are predicted surface residues on opposite faces of the protein.