*Review* **The E**ff**ect of Dysfunctional Ubiquitin Enzymes in the Pathogenesis of Most Common Diseases**

**Gizem Celebi 1, Hale Kesim 1, Ebru Ozer 1 and Ozlem Kutlu 2,3,\***


Received: 16 June 2020; Accepted: 18 July 2020; Published: 1 September 2020

**Abstract:** Ubiquitination is a multi-step enzymatic process that involves the marking of a substrate protein by bonding a ubiquitin and protein for proteolytic degradation mainly via the ubiquitin–proteasome system (UPS). The process is regulated by three main types of enzymes, namely ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3). Under physiological conditions, ubiquitination is highly reversible reaction, and deubiquitinases or deubiquitinating enzymes (DUBs) can reverse the effect of E3 ligases by the removal of ubiquitin from substrate proteins, thus maintaining the protein quality control and homeostasis in the cell. The dysfunction or dysregulation of these multi-step reactions is closely related to pathogenic conditions; therefore, understanding the role of ubiquitination in diseases is highly valuable for therapeutic approaches. In this review, we first provide an overview of the molecular mechanism of ubiquitination and UPS; then, we attempt to summarize the most common diseases affecting the dysfunction or dysregulation of these mechanisms.

**Keywords:** ubiquitination; E3s; DUBs; UPS; cancer; neurodegenerative disease; immune-related diseases
