Journal of Food Biotechnology Research

The ubiquitin (Ub) system plays a pivotal role in protein homeostasis by regulating the turnover of proteins important during a plethora of regulatory pathways like DNA damage and repair, cell cycle progression, apoptosis, receptor-mediated endocytosis, and signal transduction. Alterations in this pathway often lead to pathological conditions for the host. The Ub pathway involves an unusual combination of many specific enzymatic proteins that target nearly all short-lived and abnormal proteins for proteasomal degradation. The half-life of each protein is precisely regulated and the degradation is extremely selective and controlled at the level of ubiquitination. The role of Ub as a proteolytic signal and therefore the requirement of such highly organized machinery for the formation of an isopeptide bond between Ub and a substrate have been well characterized.

The Ub–Ub isopeptide bond may be a major contributor within the sorting of substrates for either degradation or another physiological function. Deubiquitinating enzymes (DUBs) further add complexity to the present scheme by acting as proof-reading enzymes and thus increasing the specificity of this technique. The existence of distinct Ub chains, differing only in the number of Ub–Ub linkages, not only complicates the process but also reveals the potential of alternative molecular mechanisms taking place as a result of ubiquitination, other than degradation.