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Functional analysis of discoidin domain receptors binding to lipids and collagen

Discoidin Domain Receptors (DDR1 and DDR2), are widely expressed Receptor Tyrosine Kinases (RTKs) and are found upregulated in several malignancies. DDRs share an unusual extracellular domain (ECD) that is homologous to a repeated region found in lactadherin, and blood coagulation factors V and VIII. It is well known that lactadherin and factors V and VIII bind to lipids in their ECD. Both lactadherin and factor VIII bind via a steroselective interaction with the phospho‐L‐serine motif of phosphatidylserine (Ptd‐L‐Ser). Only factor VIII binding is enhanced by the presence of phosphatidylethanolamine (PE). Factor V is stereoselective in that it appreciatively binds to L‐α‐glycerolphosphoryl‐L‐serine as opposed to the D form. All three proteins share strong homology via hydrophobic residues in their ECD. These same hydrophobic residues are conserved in the ECD of DDR1 and DDR2. To date, no studies exist indicating preferential binding of lipids to DDRs, and collagen is the only known ligand for DDRs. The effects lipids have on DDR expression and collagen‐induced activation have yet to be investigated. It is our goal to investigate DDR‐lipid (Ptd‐L/D‐Ser, phosphatidylcholine, and PE) interactions using a series of biochemical, biophysical and cell‐based techniques. The interaction of DDRs with lipids may provide a novel mechanism for understanding and modulating the functionality of DDRs.