Figure 7: Schematic models summarize TTN5 kinetic GTPase activities and potential localization within the cell.

(A), Model of the predicted GTPase nucleotide exchange and hydrolysis cycle mechanism of TTN5 based on the biochemical investigation. TTN5 affinity to mGppNHp was 9.2-fold higher compared to mGDP resulting in a fast switching from an inactive GDP-loaded form to an active GTP-loaded one. mGppNHp dissociation was 8-fold faster as GTP hydrolysis but both processes were much slower than nucleotide association. TTN5 kinetics identified it as a non-classical GTPase which tended to stay in a GTP-loaded form even under resting conditions. (B), Presumed TTN5 locations within the cell. TTN5 (green square) can be present at the plasma membrane (PM) similar as FM4–64 (red circle) or in the endomembrane compartments of the trans-Golgi network (TGN) or multivesicular body (MVB) as found by colocalization with ARA7 (red hexagon). Additionally TTN5 might colocalize with GmMan1-positive (red square) Golgi stacks.