Fig. 5: Binding model of Hsp70 to the lysosomal membrane at different lumen pH.

The blue spheres represent BMP head, while the grey spheres represent the zwitterionic phospholipids. At pH 5.3 Hsp70 keeps a native-like fold and the NBD becomes immersed in the membrane, whereas the SBD binds peripherally. The elements coloured in red depict the interacting regions. At a pH between 4.5 and 5, Hsp70 adopts a “molten globule” conformation and the NBD interaction to the membrane is mostly mediated by unspecific electrostatic interactions (indicated by red dots) to the anionic BMP.