title: Tmem27 dimerization, deglycosylation, plasma membrane depletion, and the extracellular Phe-Phe motif are negative regulators of cleavage by Bace2.
abstract: The pancreatic β-cell surface protein Tmem27 is promotes the preservation of functional β-cell mass. It is a selective substrate of the protease Bace2, yet the intramolecular features of Tmem27 that regulate its processing by this sheddase have not been characterized. In particular, the importance of homodimerization, glycosylation, trafficking to the plasma membrane (PM), the existence of multiple cleavage sites, and the amino acid residues that govern these features are currently unknown. Using Tmem27 mutational analysis and multiple biochemical approaches, we here show that Tmem27 dimerization is a dynamic process mediated by its intracellular cysteine residue and that prevents Tmem27 cleavage, that extracellular asparagine glycosylation is essential for Tmem27 trafficking to the PM and its processing by Bace2, that the amount of Tmem27 at the PM is proportional to its total cell levels upon glucose stimulation and Bace2 inhibition, and that the double phenylalanine motif in the Tmem27 cleavage site is an intramolecular Bace2 inhibitor. These findings define structural properties of Tmem27 that affect the susceptibility to its protease Bace2 and have implications for the efficiency with which Tmem27 and other Bace2 substrates are cleaved in normal and disease states.
authors.affiliation: Institute of Molecular Systems Biology, ETH Zurich, Wolfgang-Pauli Strasse 16, CH-8093 Zurich, Switzerland.
authors.forename: Daria
authors.initials: D
authors.lastname: Esterházy
authors.forename: Pinar
authors.initials: P
authors.lastname: Akpinar
authors.forename: Markus
authors.initials: M
authors.lastname: Stoffel
mesh_terms: D020816:Amino Acid Motifs; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D010649:Phenylalanine / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D055503:Protein Multimerization / Q000187:drug effects; D020836:Protein Structure, Quaternary; D021381:Protein Transport / Q000187:drug effects
chemical_list: C509285:Bace2 protein, mouse; C429534:CLTRN protein, human; D008562:Membrane Glycoproteins; D011480:Protease Inhibitors; D010649:Phenylalanine; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; D005947:Glucose