Interaction of membrane proteins with surfactants: insights into binding and stability

Manipulation of membrane proteins outside native cell embranes is challenging as these proteins are often characterized by poor stability in surfactant solutions. Understanding how surfactants self-assemble around membrane proteins and affect their stability is the key to increase success rates in their crystallization and functional studies. Here analytical ultracentrifugation and small-angle neutron scattering with contrast variation experiments have been used to characterize binding of alkyl polyglucoside surfactants to bacteriorhodopsin. Results show that bound surfactant monomers do not correlate with micellar aggregation numbers even for small and predominantly hydrophobic membrane proteins, and that the mode of binding shifts from monolayer to larger shell with increasing the surfactant chain length. Moreover, stability studies indicate that the monolayer type of binding results in limited stability of bacteriorhodopsin under different solution conditions, including light illumination. These results shed light on the origin of stability of membrane proteins in surfactant solutions and are useful in the choice of optimal surfactant environments for membrane protein studies.