The curvature sensitivity of membrane-binding amphipathic helices can be modulated by the electrostatics of their flanking regions

Membrane-induced amphipathic helices (m-AH) can act as membrane curvature sensors by binding preferentially to hydrophobic lipid packing defects enriched in curved surfaces. Weak electrostatic interactions can impart a greater reliance on hydrophobicity and membrane curvature for binding. I probed the role of modifying membrane and protein charge on the curvature sensing of two m-AH containing proteins, CTP:phosphocholine cytidylyltransferase (CCT) and alpha-synuclein (alpha-syn). The m-AH in both proteins are flanked by disordered tails with multiple phosphoserines (CCT) or acidic residues (alpha-syn), which I mutated to glutamate or serine to modify protein charge. Analysis of binding to vesicles of varying curvature showed that increasing negative charge of the tail region decreased binding strength and augmented curvature dependence, which I attribute to charge repulsion. Conversely, increasing the membrane negative charge dampened the curvature dependence. Our data show that discrimination of curved vs. flat membranes with high negative charge could be modulated by phosphorylation.;Keywords: CTP:phosphocholine cytidylyltransferase; alpha-synuclein; membrane curvature sensing; phosphorylation; amphipathic helices, fluorescence, circular dichroism, lipid vesicles.