New Insights Into the Role of Ubiquitylation of Proteins

Posttranslational modification of proteins by the addition of ubiquitin and related modifiers has an essential role in cellular processes such as protein degradation and subcellular localization. This impacts on the study of cell and developmental biology in diseases such as cancer, and on the study of protein folding and stability in Alzheimer's disease and other diseases of protein aggregation and misfolding. Recently, there have been many additions to the ubiquitylation literature that have challenged, revised, and expanded our understanding and future directions of this process. Here we present a comprehensive overview of the classical textbook description of protein ubiquitylation and then review the recent literature that has challenged and revised the canonical models of protein ubiquitylation. We discuss the roles of noncanonical ubiquitylation at sites other than lysine residues, unconventional ubiquitylation of mixed and branched polyubiquitin chains, and highlight the role of other structural and posttranslational modifications in ubiquitylation that have been identified in the recent literature. By highlighting the assumptions that have been challenged and revised in the field of protein ubiquitylation, we hope to stimulate further study and questions about this ubiquitous protein modification.