Membrane proteins are important biomolecular targets in drug discovery. Different membrane mimetics and purification strategies have been developed; however, investigating membrane proteins in their native environment remains challenging. Here, we introduce an anionic, dendritic polyglycerol sulfate (dPGS–PCL) to membrane protein research. dPGS–PCL enables the purification of soluble, protein-containing membranes. We examine the utility of dPGS–PCL to study membrane protein delipidation and function in detail. Our data show that protein yields and delipidation outcomes depend on the properties of both membrane mimetics and membranes. This allows us to re-evaluate the importance of mildly delipidating detergents for the purification of functional membrane proteins. In addition to bacterial membrane proteins, dPGS–PCL enables the purification of a functional G-protein-coupled receptor (GPCRs). We anticipate that dPGS–PCL will enable the discovery of custom-made membrane mimetics and purification protocols for future applications in membrane protein research.