Mechanisms of Intracellular Protein Transport and Targeting in Plant Cells

Abstract

The specificity of protein targeting processes is the basis of maintaining structural and functional integrity of the cell, enabling the various subcellular compartments to carry out their unique metabolic roles. Studies in plants have progressed markedly in the last 5 years, and many of the specific signals involved in the transport and targeting of proteins to the nucleus, chloroplast, mitochondrion and microbody, and to organelles along the secretory pathway (endoplasmic reticulum [ER], Golgi complex, and vacuole) have been characterized. Exciting prospects include the identification of receptors involved in the recognition of protein targeting signals, mechanisms of vesicle targeting, and the role of mRNA targeting. Although important exceptions exist, a striking feature of the mechanisms and cellular machinery of protein targeting is their universality — among plants, animals, and eukaryotic microorganisms — and even between prokaryotes and eukaryotes. More information is required about the structural features of proteins that allow for their stable accumulation in a particular subcellular compartment, of particular interest to the plant genetic engineer. Our understanding of the rules that govern protein folding and oligomer assembly and how these processes relate to a protein's ultimate stability in the cell is limited.

Key Words:

• protein targeting
• protein folding
• protein assembly
• protein stability
• secretory pathway
• molecular chaperone