Ros: c-Ros protein-tyrosine kinase (vertebrates)

Abstract

Ros is a receptor-type PTK whose ligand remains unknown. Ros has been speculated to be involved in early development of kidney collecting tubules and intestinal villi in mouse and chicken, and perhaps their mature function as well in chicken. Ros shares closest homology in sequence and structural hierarchy with Drosophila melanogaster (D. melanogaster )Sev. After Sev, the PTK domain of Ros is most similar to those of insulin receptor InsR and insulin-like growth factor I receptor IGFR. Ros contains a very large extracellular domain with 37 potential N-linked glycosylation sites and eight fibronectin type III repeats, which are spatially conserved in D. melanogaster Sev. Overall, the Ros EC domain is 20% identical in sequence with that of Sev. A Cys-rich sequence close to the N-terminus is present in chicken, human, and rat Ros. The kinase domain of chicken Ros is 58% identical with that of Sev. The PTK domain contains a unique 5-6 residue insertion, and a characteristic cluster of three tyrosine residues, which are the major autophosphorylation sites and are shared among Ros, InsR, IGFR, and Sev. The enzyme is assayed by autophosphorylation, or by phosphorylation of exogenous substrates, such as denatured enolase, casein, or bacterial lysozyme.