title: Selective interaction of megalin with postsynaptic density-95 (PSD-95)-like membrane-associated guanylate kinase (MAGUK) proteins.
abstract: Megalin is an integral membrane receptor belonging to the low-density lipoprotein receptor family. In addition to its role as an endocytotic receptor, megalin has also been proposed to have signalling functions. Using interaction cloning in yeast, we identified the membrane-associated guanylate kinase family member postsynaptic density-95 (PSD-95) as an interaction partner for megalin. PSD-95 and a truncated version of megalin were co-immunoprecipitated from HEK-293 cell lysates overexpressing the two proteins, which confirmed the interaction. The two proteins were found to be co-localized in these cells by confocal microscopy. Immunocytochemical studies showed that cells in the parathyroid, proximal tubuli of the kidney and placenta express both megalin and PSD-95. We found that the interaction between the two proteins is mediated by the binding of the C-terminus of megalin, which has a type I PSD-95/ Drosophila discs-large/zona occludens 1 (PDZ)-binding motif, to the PDZ2 domain of PSD-95. The PSD-95-like membrane-associated guanylate kinase ('MAGUK') family contains three additional members: PSD-93, synapse-associated protein 97 (SAP97) and SAP102. We detected these proteins, apart from SAP102, in parathyroid chief cells, a cell type having a marked expression of megalin. The PDZ2 domains of PSD-93 and SAP102 were also shown to interact with megalin, whereas no interaction was detected for SAP97. The SAP97 PDZ2 domain differed at four positions from the other members of the PSD-95 subfamily. One of these residues was Thr(389), located in the alphaB-helix and part of the hydrophobic pocket of the PDZ2 domain. Surface plasmon resonance experiments revealed that mutation of SAP97 Thr(389) to alanine, as with the other PSD-95-like membrane-associated guanylate kinases, induced binding to megalin.
authors.affiliation: Department of Medical Biochemistry and Microbiology, Uppsala University, PO Box 582, SE-751 23 Uppsala, Sweden. Marten.Larsson@imbim.uu.se
authors.forename: Mårten
authors.initials: M
authors.lastname: Larsson
authors.forename: Göran
authors.initials: G
authors.lastname: Hjälm
authors.forename: Amos M
authors.initials: AM
authors.lastname: Sakwe
authors.forename: Ake
authors.initials: A
authors.lastname: Engström
authors.forename: Anna-Stina
authors.initials: AS
authors.lastname: Höglund
authors.forename: Erik
authors.initials: E
authors.lastname: Larsson
authors.forename: Robert C
authors.initials: RC
authors.lastname: Robinson
authors.forename: Christian
authors.initials: C
authors.lastname: Sundberg
authors.forename: Lars
authors.initials: L
authors.lastname: Rask
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D051528:Guanylate Kinases; D006801:Humans; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009703:Nucleoside-Phosphate Kinase / Q000378:metabolism*; D010280:Parathyroid Glands / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques
chemical_list: D026561:Low Density Lipoprotein Receptor-Related Protein-2; D009419:Nerve Tissue Proteins; D025521:Tumor Suppressor Proteins; C033652:postsynaptic density proteins; D009703:Nucleoside-Phosphate Kinase; C496468:DLG2 protein, human; D051528:Guanylate Kinases