The Biology of LR11

Research project P 13940 The Biology of LR11 Wolfgang Johann SCHNEIDER 11.10.1999 Recently, several new members of the Low Density Lipoprotein receptor (LDLR) supergene family have been discovered. To date, very little is known about their cell biological, biochemical, and functional properties._ One of the most complex molecules of the family known is LR11 (also called sorLA), which contains 11 typical LDLR binding repeats (hence its name), domains similar to a yeast receptor for vacuolar carboxypeptidase Y (Vps10p domain) and to EGF, 6 fibronectin III repeats, a transmembrane stretch, and a short cytoplasmic tail. LRIls are extremely highly conserved in chicken (the model system in my research group for the past 12 years), man, mouse, rabbit, and the rat, and are expressed predominantly in brain, but are also found in testes, ovary, kidneys, pancreas, and, in some species, in the liver. Since first results of collaborative studies towards the generation and characterization of genetic mouse models do not promise immediate insights into the biology of LR11, we will use a combination of experiments in selected cellular systems to delineate the biological properties of LR11. Our preliminary studies on LR11 have concentrated on the production of tools for the studies proposed here. The resarch plan consists of four parts, which will be tackled in a coordinated fashion. 1) We will use antibodies to elucidate the biosynthetic pathway, subcellular localization, and endocytic activity of LR11 in cell systems already shown to be suitable for these studies. 2) With molecular biological approaches, we will determine the cell-specific expression of LR11 in tissues of interest, such as the brain and gonads; the suggestion of the existence of splice variant forms of LR11 will be followed up. 3) In biochemical studies, we will determine the ligand binding properties of LR11; besides known ligands of the LDLR family, we will test for the binding. of candidate proteins arising from the unique extracellular features of LR11. 4) Recently, several LDLR family members have been shown to interact, via their cytoplasmic domains, with intracellular adapter proteins; the short cytoplasmic tails of LR11s are extremely highly conserved among 5 species (up to 100%) and show many similarities to those of other family members, as well as unique features. Thus, a search for LR11 -adapter proteins will be performed by a two-pronged interaction screening approach using yeast- 2-hybrid and phage-display. In summary, I am confident that these studies will provide signicant advances in our understanding of the biology of LR11, a fascinating membrane protein.