Protein Sorting in the Secretory System of Plant Cells

Abstract

This chapter describes the protein sorting in the secretory system of plant cells. Each organelle of the eukaryotic cell contains a distinct set of proteins that determines the structure and biochemical activities of that organelle. There are true sorting signals that direct proteins along branched pathways such as that encountered at the trans-Golgi network (TGN), where the pathways of constitutive and regulated secretory proteins, proteins destined for different domains of polar cells, and proteins destined for the lytic compartment diverge after having shared a common route through the endoplasmic reticulum (ER) and Golgi apparatus. The positive targeting information is carried by the primary translation product. The transport competence of proteins in the secretory pathway is also dependent on protein conformation. The ER is the site of the initial steps of N-linked glycosylation, and of protein folding and oligomerization. If these steps are blocked by mutations, drug treatment, or synthesis of single polypeptides from heteromeric proteins, the misassembled, malfolded proteins may fail to exit the ER.