The present invention provides moieties that bind to an Ig-like domain, e.g., D4 or D5, of a human receptor tyrosine kinase, e.g., the human Kit RTK or the PDGFR RTK, or the D7 domain of a type V receptor tyrosine kinase wherein the moieties lock the ectodomain of the receptor tyrosine kinase in an inactive state thereby antagonizing the activity of the receptor tyrosine kinase.