Untangling structural molecular details of the endocytic adaptor protein CALM upon binding with phosphatidylinositol 4,5-bisphosphate-containing model membranes

Clathrin assembly lymphoid myeloid leukemia protein (CALM) is involved in the formation of clathrin-mediated endocytic coats by virtue of binding many proteins involved in the process, including clathrin itself and AP2 cargo adaptor complex. CALM is able to specifically recognize the inner leaflet of the plasma membrane by binding the membrane’s phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P ₂ ). Here, a biophysical approach, primarily using neutron and X-ray scattering and solid-state NMR experiments, was exploited to investigate CALM interaction with PtdIns(4,5)P ₂ -presenting model membranes. The presented experimental data reveal how the CALM folded domain is partly accommodated within the lipid membrane, directly interacting with PtdIns(4,5)P ₂ phosphates. Moreover, these data suggest that CALM’s amphiphilic N-terminal helix buries into the membrane, not only stabilising the protein docking to the membrane but also providing a mechanism to induce membrane curvature.