title: The cytosolic tail of the tumor marker protein Trop2--a structural switch triggered by phosphorylation.
abstract: Trop2 is a transmembrane signaling glycoprotein upregulated in stem and carcinoma cells. Proliferation-enhancing signaling involves regulated intramembrane proteolytic release of a short cytoplasmic fragment, which is later engaged in a cytosolic signaling complex. We propose that Trop2 function is modulated by phosphorylation of a specific serine residue within this cytosolic region (Ser303), and by proximity effects exerted on the cytosolic tail by Trop2 dimerization. Structural characterization of both the transmembrane (Trop2TM) and cytosolic regions (Trop2IC) support this hypothesis, and shows that the central region of Trop2IC forms an α-helix. Comparison of NMR structures of non-phosphorylated and phosphorylated forms suggest that phosphorylation of Trop2IC triggers salt bridge reshuffling, resulting in significant conformational changes including ordering of the C-terminal tail. In addition, we demonstrate that the cytosolic regions of two Trop2 subunits can be brought into close proximity via transmembrane part dimerization. Finally, we show that Ser303-phosphorylation significantly affects the structure and accessibility of functionally important regions of the cytosolic tail. These observed structural features of Trop2 at the membrane-cytosol interface could be important for regulation of Trop2 signaling activity.
authors.affiliation: Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia.
authors.forename: Miha
authors.initials: M
authors.lastname: Pavšič
authors.affiliation: 1] Slovenian NMR Centre, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia [2] EN-FIST Centre of Excellence, Dunajska 156, SI-1000 Ljubljana, Slovenia.
authors.forename: Gregor
authors.initials: G
authors.lastname: Ilc
authors.affiliation: Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia.
authors.forename: Tilen
authors.initials: T
authors.lastname: Vidmar
authors.affiliation: 1] Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia [2] Slovenian NMR Centre, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia [3] EN-FIST Centre of Excellence, Dunajska 156, SI-1000 Ljubljana, Slovenia.
authors.forename: Janez
authors.initials: J
authors.lastname: Plavec
authors.affiliation: 1] Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia [2] J. Stefan Institute, Department of Biochemistry, Molecular and Structural Biology, Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Brigita
authors.initials: B
authors.lastname: Lenarčič
mesh_terms: D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm / Q000737:chemistry* / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules; D021122:Protein Subunits; C499380:TACSTD2 protein, human