Table 1: Statistics on Data Collection and Refinement

Structure ARNO Arf1-GDP-Mg2+- Arf1[17] -GDP- Arf1[17] -GDP- BFA-ARNO Mg2+-BFA-ARNO ARNO[E156K] Data Collection

Space Group P21 P212121 P41212 P3221 Unit Cell a (Å) 33.429 69.081 111.462 104.018 b (Å) 95.775 109.773 111.462 104.018 c (Å) 33.665 118.326 74.534 69.277  (°) 101.670 ESRF Beam line BM30A/ID14-EH2 ID14-EH3 BM30A ID14-EH3

Wavelength (Å) 0.979/0.933 0.931 0.980 0.931 Resolution limits (Å) 33 – 1.70 25 – 1.86 30 - 1.80 30 - 1.46 high resolution shell 1.75-1.70 1.88-1.86 1.85-1.80 1.47-1.46 Reflections: measured 95944 881407 525012 1199546 unique 21082 74905 43814 75051

Completeness (%) 91.4 (65.5)* 97.1 (83.6)* 98.8 (97.1)* 99.3 (97.0)*

Rsymm (%) 6.6 (12.2)* 8.7 (42.4)* 5.0 (40.5)* 5.9 (46.2)* I /  18.0 (5.0)* 18.6 (3.1)* 26.2 (6.4)* 26.6 (5.9)* Refinement

Reflections Rcryst / Rfree 19998 / 1083 71213 / 3692 41588 / 2225 71298 / 3744

Rcryst (%) 20.2 (24.8)* 18.0 (23.4)* 18.3 (25.1)* 16.1 (21.2)*

† Rfree (%) 23.2 (26.5)* 22.2 (28.0)* 22.1 (25.6)* 17.3 (21.8)* Protein atoms 1594 6035 2876 2835 Heterogen atoms 4 107 49 50 Water molecules 115 348 286 351 Average B factor (Å2) 20.3 28.6 20.9 14.5 R.m.s.d. bond length (Å) 0.029 0.025 0.026 0.015 R.m.s.d. angles length (°) 2.087 1.950 2.001 1.412 * Values in parentheses correspond to high resolution shell in data collections † 5 % of the reflections were set aside for an Rfree test before initiating any refinement