Structural Insights into a Unique Legionella pneumophila Effector LidA Recognizing Both GDP and GTP Bound Rab1 in Their Active State
Figure 4
The complexed GDP-bound Rab1 (S25N) is held in the active conformation.
(A) Superimposition of GDP-bound Rab1(S25N)-LidA complex and GTP-bound Rab1-LidA complex (left). The Fo-Fc electron density of GDP and GTP/Mg2+ in the two complexes is shown (right), respectively. The Figure demonstrates the quality of the electron density (blue mesh). Both of the electron density are depicted at 3.0 σ. (B) Superimposition of LidA-bound GDP-Rab1(S25N) and LidA-bound GTP-Rab1(WT). (C) Superimposition of LidA-bound GDP-Rab1(S25N) and free GDP-Rab1 (PDB ID code 2FOL). The largest displacement of 9.2 Å at the Cα atom of Ile in Switch I is shown. The disordered broken switch II in 2FOL is shown by blue dashed lines. The switch regions and P-loops are highlighted in different colors indicated in the color-box to contrast their conformational changes. (D and E) The C-terminal region of LidA contributes to maintain the GDP-bound Rab1(S25N) in active conformation. LidA(418-559) is shown with electrostatic surface potentials. (D) GDP-Rab1 switch I region is stabilized through the interaction with LidA α7 helix. (E) Switch II region is stabilized both by polar interaction with the loop linking LidA α6 and α7 and hydrophobic contacts with LidA α5 helix; Blue and red represent the positive and negative charge potential, white represent the hydrophobic contacts. Switch regions are color-coded as before. (F) Quantitative analysis of two ITC runs: titration of GTP-bound Rab1(Q70L) (left) and GDP-bound Rab1(S25N) (right) into LidA(188-449), respectively. Both titrations were performed in the absence of added Mg2+ and GDP/GTP. The KD value is 0.43 µM for GTP-bound Rab1(Q70L) and 2.4 µM for GDP-bound Rab1(S25N), respectively.