Spitz (protein)

Spitz is a protein in fruit flies which is the major activator of Epidermal Growth Factor Receptor (EGFR).
Function.
Spitz is produced as a transmembrane protein in the endoplasmic reticulum. There it associates with a cargo receptor called "Star" and is trafficked to the Golgi. In the Golgi, Spitz is cleaved by a protease called "Rhomboid", which releases Spitz to be trafficked to the cell membrane and released out of the cell. From here it can bind EGFR on the surface of other cells, activating the receptor. Alternatively, Spitz can be bound and inactivated by Argos, inhibiting EGFR activation.
Structure.
Spitz is structurally similar to TGF-α.