Ubiquitination (ubiquitinylation) is a post-translational modification (PTM) process, where a ubiquitin is added to a lysine/cysteine/ serine/threonine of a substrate protein via the C-terminal glycine of ubiquitin. It is essential for balancing numerous physiological processes. Through altering proteins' degradation, cellular location, activity, and interactions with other molecules, ubiquitination regulates protein functions in relevant signaling pathways.