(757b) Elucidating Molecular Mechanisms for Membrane Geometry-Specific Protein Localization

Cellular membranes are polymorphic, that is they have distinct shapes/geometries which have been observed to confer specific functions. However, the molecular mechanisms underlying the plethora of phenomenological structure/function correlations remain elusive. This is largely due to the difficulty of controlling and investigating membrane geometry, which has historically been a significant impediment to experimental observation. As a result, our limited knowledge of the properties of membrane shapes relies on work that investigated the influence of mean curvature, but not geometry, on membrane properties.

We studied the effect of membrane geometry on membrane-bound protein localization. We will present our molecular-field theory calculations along with quantitative comparative experiments with controlled spherical and cylindrical membrane geometries (the two most abundant cellular membrane geometries). To increase the biological relevance and impact of our work we extended our investigation to three major classes of such membrane-binding domains: amphipathic helices, C2-domains and lipidated anchors.

Our experimental results in combination with state of the art molecular-field theory calculations revealed several incisive key findings and the underlying physical and molecular mechanisms:

1. All tested membrane-binding domains were for the first time shown to be able to discriminate spherical from cylindrical membrane geometries.
2. Contrary to existing theoretical predictions and common wisdom, all tested membrane-binding domains were able to discriminate geometries of same mean curvature, revealing the crucial but hitherto neglected contribution of Gaussian curvature.
3. The tested membrane-binding domains exhibited a dramatic variation in the ability to discriminate geometries (from 2-fold to 40-fold), revealing specificity in the synergistic interaction between protein and membrane geometry and thus suggesting adaptation.
4. Molecular-field theory revealed that the molecular mechanism underlying the observations is the effect of Gaussian curvature on only two of the four terms of the interaction potential (the excluded volume and the hydrophobic interaction terms). Thus, demonstrating for the first time how geometry can affect membrane-proteins interactions at the atomic level.

Because a plethora of biological processes depend on the properties of membranes, these results establish a mechanistic basis for understanding why distinct membrane geometries can have a specific effect on cellular membrane biology. They also reveal protein segregation as a new biological function of membrane polymorphism.