LDL receptor family: isolation, production, and ligand binding analysis

Members of the low density lipoprotein receptor gene family have recently received particular attention because of their involvement not only in lipoprotein transport, but also in signal transduction pathways. The main characteristic feature of this protein group is their cysteine-rich ligand binding domain, which is able to bind many unrelated proteins, such as apolipoproteins, proteases, and protease/inhibitor complexes, signaling molecules such as reelin, and several other groups of proteins. The main challenges of studying these proteins in vitro are their extremely high content of disulfide bridges and the detergent-sensibility of their classical ligands, i.e, lipoproteins. Here, we describe generally applicable procedures for the analysis of these receptors. We present an outline of established methodology for their isolation and visualization, the production of recombinant fragments, in particular of soluble ligand binding domains, and we describe standard procedures for the analysis of the functionality of the receptors and recombinant receptor ligand binding fragments, respectively.