Targeting tail-anchored proteins into plant organelles

Abstract

The extensive evolution of intracellular compartmentalization requires highly selective mechanisms for protein targeting to distinct membrane systems. One of the fundamental processes in protein targeting is the insertion of proteins into biological membranes. The efficient and accurate insertion of membrane proteins is an important step for their proper function in different organelles, and any targeting error may lead to mislocalization of these proteins with detrimental cellular effects. Posttranslational insertion is required for a class of tail-anchored (TA) proteins, which are characterized by a transmembrane domain (TMD) near their C terminus, for their correct targeting to the destined membrane (1). In PNAS, Xing et al. uncover a pathway for TA protein insertion into the endoplasmic reticulum (ER) in the model plant Arabidopsis thaliana , which plays an unexpected role in root hair growth (2). The authors identify several key components in the guided entry of tail-anchored protein (GET) complex that has a conserved function in regulating TA protein insertion. However, in contrast to yeast and animals, the core GET system in Arabidopsis involves a distinct GET3 clade, suggesting an ancient evolution of the GET3 paralogs in plants and which may function divergently as plant-specific organelle chaperones. The GET pathway is the most extensively studied system for shuttling TA proteins to distinct organelles in yeast and mammalian cells. Structural and biochemical investigations in yeast have provided insights into the molecular mechanism of the GET complex (1). In the yeast GET pathway, newly synthesized TA proteins are initially recognized by a cytosolic pretargeting complex (PTC), comprising SGT2 and GET4–GET5, and then transferred to the ATPase GET3. GET3 loaded with a TA protein will then bind to its receptor: the ER-localized GET1–GET2 complex, which subsequently promotes the insertion of the TA protein into the ER membrane (Fig. 1 A ). The recognition and insertion processes mediated … [↵][1]1To whom correspondence should be addressed. Email: ljiang{at}cuhk.edu.hk. [1]: #xref-corresp-1-1