Alternative Splicing of a Receptor Intracellular Domain Yields Different Ectodomain Conformations, Enabling Isoform-Selective Functional Ligands
Fouad Brahimi,
Alba Galan,
Sean Jmaeff,
Pablo F. Barcelona,
Nicolas De Jay,
Kurt Dejgaard,
Jason C. Young,
Claudia L. Kleinman,
David Y. Thomas,
H. Uri Saragovi
Affiliations
Fouad Brahimi
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
Alba Galan
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
Sean Jmaeff
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada; Department of Pharmacology, McGill University, Montreal, QC, Canada
Pablo F. Barcelona
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada
Nicolas De Jay
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada; Department of Human Genetics, McGill University, Montreal, QC, Canada
Kurt Dejgaard
Department of Biochemistry, McGill University, Montreal, QC, Canada
Jason C. Young
Department of Biochemistry, McGill University, Montreal, QC, Canada
Claudia L. Kleinman
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada; Department of Human Genetics, McGill University, Montreal, QC, Canada
David Y. Thomas
Department of Biochemistry, McGill University, Montreal, QC, Canada
H. Uri Saragovi
Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada; Department of Pharmacology, McGill University, Montreal, QC, Canada; Department of Ophthalmology and Visual Science, McGill University, Montreal, QC, Canada; Corresponding author
Summary: Events at a receptor ectodomain affect the intracellular domain conformation, activating signal transduction (out-to-in conformational effects). We investigated the reverse direction (in-to-out) where the intracellular domain may impact on ectodomain conformation. The primary sequences of naturally occurring TrkC receptor isoforms (TrkC-FL and TrkC.T1) only differ at the intracellular domain. However, owing to their differential association with Protein Disulfide Isomerase the isoforms have different disulfide bonding and conformations at the ectodomain. Conformations were exploited to develop artificial ligands, mAbs, and small molecules, with isoform-specific binding and biased activation. Consistent, the physiological ligands NT-3 and PTP-sigma bind both isoforms, but NT-3 activates all signaling pathways, whereas PTP-sigma activates biased signals. Our data support an “in-to-out” model controlling receptor ectodomain conformation, a strategy that enables heterogeneity in receptors, ligands, and bioactivity. These concepts may be extended to the many wild-type or oncogenic receptors with known isoforms.
