Peptidases in Plant Tissue

Abstract

Peptidases are a diverse group of enzymes with many different catalytic mechanisms. They constitute up to 2% of the plant proteome and function in multitude of ways to ensure survival. The study of seed development and germination has revealed many peptidases that are crucial to the correct deposition of seed storage proteins in monocotyledonous and dicotyledonous plants. Under the correct environmental conditions, germination of the seed is initiated. The organised synthesis and action of peptidases ensure the hydrolysis of the storage proteins which then provides the necessary amino acids for the seedling's growth. These events have profound implications to the survival of the plant species and to the survival of ecosystems that feed on the seeds and plant material generated after germination. Peptidase activity (which can be monitored using coloured substrates) is also linked to plant senescence, programmed or regulated cell death, to the 26S proteasome which functions in normal cellular events to regulate the total cell protein and also to provide defence against pathogen invasion. The activity of these peptidases can be regulated by naturally occurring inhibitors and the differential location of substrate and enzyme. Plant peptidases (e.g. papain) are of commercial interest particularly in the meat processing industry because of their wide pH optima, thermostability and their ability to work on heterogeneous substrates. Key Concepts Peptidases are the principal enzymes in the catabolism of proteins and peptides. Seed germination is an event in which the stored carbohydrate, lipid and protein in the seed is hydrolysed and used for the synthesis of new macromolecules vital for the emerging plant's growth. Plant programmed cell death is the death of a cell responding to a variety of extracellular and intracellular signals. Endomembrane flow is the dynamic movement of lipid and protein from the endoplasmic reticulum through the Golgi bodies to the plasma membrane or storage vesicles. Signal peptides are small specific sequences at the N ‐terminus of a proteins sequence to designate which organelle the protein should be directed to.

The FtsHi Enzymes of Arabidopsis thaliana: Pseudo-Proteases with an Important Function

“…Plant proteases associated with a particular proteolytic activity are present in various cellular compartments and organelles constituting up to 3% of the plant proteome [5,6]. Proteases are classified according to their catalytic types.…”