Molecular Insights into the Collagen-binding Specificity of Discoidin Domain Receptors
Discoidin domain receptors, DDR1 and DDR2, are a subfamily of homologous receptor tyrosine kinases that are activated by the extracellular matrix (ECM) collagens. Together the two DDRs recognize at least seven of the twenty-eight known collagen types (Col1-28) with distinct specificities. For example, Col1-3 and Col5 that exist as fibres in connective tissues activate both DDRs whereas Col6 microfilaments found in ECM of skeletal muscles preferentially activates DDR1. Further, Col4 found in basement membrane as mesh-like networks preferentially activates DDR1 but similarly network-forming Col10 abundant in cartilage preferentially binds and activates DDR2. These preferential interactions activate specific signalling pathways driving distinct physiological processes and pathologies, yet their molecular basis is currently not understood. Here, we show that the collagen-binding specificity of the DDRs is determined by electrostatic interactions at the receptor-ligand binding interface. The collagen-binding site in the two DDRs differ in the nature and placement of electrostatically charged residues. The known DDR-binding epitopes in Col1-Col3 also contain charged residues positioned to interact with those on the DDRs. We hypothesize that these interfacial electrostatic interactions between the DDRs and collagens guide their recognition specificity. We experimentally test this hypothesis and show that triple-helical peptides (THPs) containing rationally placed charged residues have biased affinities for the two DDRs. Aside from advancing mechanistic understanding of the different collagen-DDR interactions, our results can facilitate better understanding of the associated signalling pathways and the design of therapeutically active DDR-specific antagonists.