<i>Legionella</i> and <i>Rickettsia</i> RalF proteins are autoinhibited by their capping domain <i>in vitro</i>.

<p><b>A</b>) Alignment of the <i>Legionella</i> and <i>Rickettsia</i> RalF full length proteins. <b>B</b>) Structural organization of LpRalF protein. Ribbon rendering showing LpRalF Sec7 domain (blue), linker (orange) and capping domain (white) (Protein Data Bank accession code 1XSZ, image generated with PyMOL (<a href="http://pymol.sourceforge.net" target="_blank">http://pymol.sourceforge.net</a>)) <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003012#ppat.1003012-Amor1" target="_blank">[22]</a>. The Sec7 catalytic glutamic acid side chain is represented as a stick with oxygen atoms shown in red. <b>C</b>) LpRalF and RpRalF Sec7 domains activate His-ΔN17Arf1 <i>in vitro</i>. Efficiency of His-ΔN17Arf1 nucleotide exchange catalyzed by the indicated MBP-tagged proteins. K_cat/K_m values were obtained as described in Materials and Methods. Average and standard deviation are calculated from three independent experiments. <b>D</b>) Efficiency of His-ΔN12Arf6 nucleotide exchange catalyzed by MBP-tagged LpRalF and RpRalF Sec7 domains. K_cat/K_m values were obtained as described in Materials and Methods. Average and standard deviation are calculated from three independent experiments. <b>E</b>) The RalF capping domain regulates GEF activity. Comparison of K_cat/K_m values for His-ΔN17Arf1 nucleotide exchanged catalyzed by the Sec7 domain and the full length RalF proteins. Average and standard deviation are calculated from three independent experiments.