Complex sentence: Ephrin receptors (Ephs) are a group of receptors that activate in response to ephrin ligand-binding and form the largest known subfamily of receptor tyrosine kinases (RTKs).
Split into simpler sentences: Ephrin receptors (Ephs) are a group of receptors are activated in response to binding ephrin. Ephs form the largest known subfamily of receptor tyrosine kinases (RTKs).