The invention is directed to a process for preparing a library of saposin lipoprotein particles, wherein the particles comprise membrane components from a cell or an organelle membrane and a lipid binding polypeptide that is a saposin-like protein belonging to the SAPLIP family of lipid interacting proteins or a derivative form thereof, wherein the process comprises the steps of a) providing a mixture of crude membrane vesicles obtained from a cell or an organelle membrane； b) contacting the mixture of step a) with the lipid binding polypeptide in a liquid environment； and c) allowing for self-assembly of the particles. The invention also provides a process for preparing a purified saposin lipoprotein particle comprising the steps of preparing a library according to the process described above and the additional step of f) purifying the saposin lipoprotein particle from the library. In addition, the invention provides a library of saposin lipoprotein particles and saposin lipoprotein particles obtainable according to the processes of the invention. These can be used in medicine, in particular in preventing, treating or lessening the severity of a disease or for use in a diagnostic method, a cosmetic treatment or for use as vaccination formulation or as a tool for drug development, drug screening, drug discovery, antibody development, development of therapeutic biologics, for membrane or membrane protein purification, for membrane protein expression, for membrane and/or membrane protein research, in particular lipidomics and proteomics, preferably for the isolation, identification and/or study of membranes and/or membrane proteins or creation of a lipidome or proteome database.
