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

doi:10.1016/j.isci.2020.101447

Alternative Splicing of a Receptor Intracellular Domain Yields Different Ectodomain Conformations, Enabling Isoform-Selective Functional Ligands

iScience. 2020 Aug 10;23(9):101447. doi: 10.1016/j.isci.2020.101447. eCollection 2020 Sep 25.

Authors

Fouad Brahimi¹, Alba Galan¹, Sean Jmaeff^{1

2}, Pablo F Barcelona¹, Nicolas De Jay^{1

3}, Kurt Dejgaard⁴, Jason C Young⁴, Claudia L Kleinman^{1

3}, David Y Thomas⁴, H Uri Saragovi^{1

2

5}

Affiliations

¹ Lady Davis Institute-Jewish General Hospital, McGill University, 3755 Côte St. Catherine, E-535, Montreal, QC H3T 1E2, Canada.
² Department of Pharmacology, McGill University, Montreal, QC, Canada.
³ Department of Human Genetics, McGill University, Montreal, QC, Canada.
⁴ Department of Biochemistry, McGill University, Montreal, QC, Canada.
⁵ Department of Ophthalmology and Visual Science, McGill University, Montreal, QC, Canada.

Abstract

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.

Keywords: Biochemistry; Biological Sciences; Structural Biology.