Recombinant Human MSPR/Ron Protein, CF

Macrophage stimulating protein receptor (MSP R), encoded by the human Ron and the mouse Stk, is one of a small family of receptor tyrosine kinases (RTKs) that also includes human Met (the receptor for hepatocyte growth factor) and chicken Sea (1, 2). This family of receptors is synthesized as a single-chain precursors that are cleaved into a mature disulfide-linked heterodimers composed of an extracellular alpha chain and a membrane spanning beta chain with intrinsic tyrosine kinase activity. Biologically active ligands (MSP and HGF) for this family of receptors are also disulfide-linked alpha-beta heterodimers. Human MSP R cDNA encodes a 1400 amino acid (aa) residue precursor protein with a 24 aa signal peptide, a 285 aa residue alpha chain (Glu25-Arg309) and a 1091 aa residue transmembrane beta chain (Gly310-Thr1400). The extracellular domain of MSP R is comprised of an N-terminal sema domain, a PSI (plexin semaphorins integrins) domain, followed by four immunoglobulin-like folds shared by plexins and transcription factors (3). The soluble sema domain binds MSP and inhibits the MSP R-dependent signaling pathways. MSP receptor is expressed in multiple tissues including specific areas of the central and peripheral nervous systems, epithelial cells along the digestive tract, skin and lung, and in subpopulations of the mononuclear phagocyte lineage (1, 2). Although free MSP alpha or beta chains have been shown to bind MSP R, only the heterodimeric MSP can induce receptor activation and cause biological activity (4, 5). MSP R associates with other transmembrane molecules including integrins, cadherins and other cytokine receptors. Transactivation and signaling crosstalk between MSP R and its associated transmembrane receptors have been demonstrated (6-8). Human MSP R shares 72% amino acid sequence identity with mouse MSP R.