Activities of MxB GTPase active site mutant proteins. (A) X-ray crystal structure of dynamin active site with bound phosphomethylphosphonic acid guanylate ester (GCP) (pdb code 3zyc). Dynamin side chain contacts with GCP (cyan backbone) are labeled, with the corresponding conserved MxB residue labeled in parenthesis. Dotted black lines denote hydrogen bonds. Remaining colors: red, oxygen atoms; blue, nitrogen; orange, phosphorus. (B) (top) WT or MxB mutant protein activities against HIV-1 (dark grey), EIAV (light grey) or FIV infection (striped). Results are an average of at least 6 independent experiments, with error bars denoting 95% confidence intervals. (bottom) Representative western blots from at least 3 independent experiments. (C) Immunofluorescent microscopy of HOS cells expressing WT MxB or the indicated mutant protein. Each bar represents a distance of 10 μm.