Two-step release of kinase autoinhibition in discoidin domain receptor 1

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase implicated in organogenesis, tissue homeostasis, and diseases like fibrosis and cancer.
• The precise regulatory mechanisms governing DDR1 kinase activity remain largely unelucidated.

Purpose of the Study:

• To investigate the role of the long intracellular juxtamembrane (JM) region of human DDR1 in regulating kinase activity.
• To elucidate the structural basis and functional consequences of JM region interactions with the DDR1 kinase domain.

Main Methods:

• Crystal structure analysis of the DDR1 kinase domain.
• In vitro enzymology using soluble kinase constructs.
• Site-directed mutagenesis and cell-based assays to assess collagen-induced DDR1 activation.

Main Results:

• The kinase-proximal JM4 segment of DDR1 forms a hairpin structure that occupies the kinase active site, contributing to autoinhibition.
• DDR1 autoinhibition is released in a two-step process: rapid phosphorylation of JM4 tyrosines (Tyr569, Tyr586), followed by slower activation loop phosphorylation.
• Mutating JM4 tyrosines abrogated collagen-induced DDR1 activation in cellular models.

Conclusions:

• The JM4 region acts as a critical autoinhibitory element in DDR1, with its phosphorylation being essential for receptor activation.
• Understanding this regulatory mechanism provides a basis for developing specific allosteric inhibitors targeting DDR1 kinase activity.