Transport of Proteases to the Vacuole: ER Export Bypassing Golgi?

Abstract

Most vacuolar proteases are transported from the endoplasmic reticulum (ER) to vacuoles via the Golgi apparatus. However, higher plants possess a unique papain- type protease, termed KDEL-tailed protease. This protease has a Lys – Asp – Glu – Leu (KDEL) sequence at its C-terminus, which is known as a retention signal of soluble pro- teins to the ER, although the protease localizes and functions in vacuoles. Investigations on the intracellular trafficking pathway of this unique enzyme have suggested that the protease is transported from the ER to vacuoles by bypassing the Golgi apparatus. In this review, Golgi-dependent vacuolar trafficking of proteases is first explained, then the Golgi-independent vacuolar transport pathway of the KDEL-tailed protease is described.