Estimating stored curvature elastic energy in biological membranes in vitro and in vivo

Correlations between stored curvature elastic energy (SCE) in biological membranes and enzymatic activity, protein folding and the mechanism by which cells modulate lipid homeostasis have been demonstrated in the literature. Disentangling such relationships from the other physical properties of biological membranes, which might also play a role in regulating enzymatic activity, protein folding and lipid homeostasis, requires reliable methods for measuring SCE in biological membranes to be developed. To date there are no methods that enable SCE to be measured directly in a membrane and therefore it is commonplace for authors to estimate the effects of lipid compositional change on SCE. These approaches tend to be qualitative and based on ‘rule of thumb’ relationships between lipid structure and lipid curvature, determined from lyotropic liquid crystal phase behaviour, or semi-quantitative, utilising measurements of lipid monolayer spontaneous curvatures to estimate the magnitude of curvature elastic stress in a membrane of differing lipid compositions. In this chapter different approaches to estimating SCE within lipid membranes, both in vivo and in vitro, are presented with the aim of enabling researchers to utilise these calculations in their own studies.