| Phospho‑DDR1/DDR2 (Tyr796/740) refers to the activated forms of the collagen receptors DDR1 and DDR2, two discoidin domain receptor tyrosine kinases that integrate extracellular matrix cues with intracellular signaling controlling adhesion, migration, and matrix remodeling. DDR1 carries a discoidin‑like collagen‑binding domain, a single transmembrane segment, a juxtamembrane region, and an intracellular kinase domain whose activation loop contains Tyr796; collagen engagement induces slow but sustained receptor autophosphorylation on multiple tyrosines, and antibodies specific for phospho‑Tyr796 detect DDR1 only in this ligand‐activated state, marking the productive kinase conformation that propagates downstream signaling. DDR2 shares a similar domain layout and is likewise activated by fibrillar collagens, but Tyr740 sits within its activation loop as a regulatory site that is phosphorylated not only during receptor autophosphorylation but also directly by Src family kinases, creating a key control point for DDR2 signaling output. Biochemical dissection of DDR2 shows that Src targets three activation‑loop residues (Tyr736, Tyr740, Tyr741); phosphorylation at Tyr740 stimulates intramolecular DDR2 autophosphorylation on additional cytoplasmic tyrosines, which then serve as docking sites for the adaptor Shc and assembly of DDR2–Shc signaling complexes, linking collagen engagement to Ras–MAPK and other Shc‑dependent pathways. Mutation of Tyr740 to phenylalanine relieves an inhibitory constraint within the activation loop, producing a receptor that displays collagen‑independent autophosphorylation and constitutive signaling, indicating that the unphosphorylated Tyr740 side chain restrains kinase activity and that its modification or substitution shifts DDR2 toward an active conformation. Across DDR1 and DDR2, phosphorylation at Tyr796 and Tyr740 therefore defines collagen‑ and Src‑responsive activation loop states that control receptor autophosphorylation, adaptor recruitment, and signal propagation into pathways regulating cell–matrix adhesion, motility, and tissue remodeling, and assays that specifically quantify phospho‑DDR1 (Tyr796) and phospho‑DDR2 (Tyr740) in lysates provide a direct biochemical readout of discoidin receptor engagement by collagen and of Src‑dependent tuning of DDR2 activity in physiological and pathological contexts. |
