FIGURE 3.

Intramembrane serine proteases. A, Rhomboid proteins contain a conserved serine and histidine, which compose the catalytic dyad of a serine protease. Rhomboid-1 cleaves within the transmembrane region of the Drosophila EGF-like growth factor Spitz. B, structure of E. coli Rhomboid GlpG. The serine in TMD4 and the histidine in TMD6 are coordinated in a manner consistent with known serine proteases and at a depth within the membrane consistent with the site of proteolysis of Rhomboid substrates.