Current Protein and Peptide Science - Volume 5, Issue 3, 2004

Protein degradation in eukaryotic cells is important for regulation of metabolism, progression through the division cycle, in cell signalling pathways, and in mammals also for generation of antigen fragments for presentation on the major histocompatibility complex (MHC) class I. Most cell proteins are degraded via the ubiquitin / proteasome pathway where an elaborate enzyme system recognises the protein substrates and marks t Read More

Proteasomes are the major nonlysosomal protein degradation machinery in eukaryotic cells and they are largely responsible for the processing of antigens for presentation by the MHC class I pathway. This review concentrates on recent developments in the area of antigen processing. Specialized proteasomes called immunoproteasomes and an 11S regulator of proteasomes (PA28) are induced by interferon-g, but it is Read More

Intracellular protein degradation is a tightly regulated process that in many cases is controlled by protein ubiquitylation. The ubiquitin pathway is a major route by which cells not only remove normal proteins at the appropriate time but also abnormally folded normal or mutant, cytoplasmic and membrane, proteins. This has led to a major impetus to identify constituents of the pathway. The key components that regulate substrat Read More

Several studies have examined the importance of ubiquitin-like posttranslational modifiers (which consist of an unexpectedly large family). Of these, NEDD8 (also called Rub1, related to ubiquitin 1) with a high homology to ubiquitin is covalently linked to all members of cullin (Cul)-family proteins through an enzymatic cascade analogous to ubiquitylation. Cul-family proteins are scaffold proteins for a wide series of ubiquiti Read More

The COP9 Signalosome (CSN), a highly conserved eight-subunit complex, is found in all higher eukaryotes. It contains eight core subunits, named CSN1 - 8, in order of decreasing molecular weight. The CSN is structurally similar to the regulatory lid of 26S proteasome and the eukaryotic translation initiation factor eIF3. CSN is also now known to play an essential role in signaling processes controlling many aspects of plant Read More

Conjugation of one or more molecules of ubiquitin to target proteins can signify one of several fates, including degradation by the 26S proteasome, or trafficking via the secretory or endocytic pathways. Whereas much attention in recent years has focussed on the mechanisms of forming these different ubiquitin conjugates, far less is known about the removal of ubiquitin, which is performed by deubiquitinating enzymes (DUBs). Read More

Covalent conjugation of the ubiquitin tag to cellular proteins plays a central role in a number of processes, the most notable among them being degradation by the 26S proteasome. A fundamental property of this process is that ubiquitination, in contrast to subsequent degradation, is reversible due to a number of deubiquitinating enzymes that mediate the disassembly of ubiquitin-protein conjugates. The uniqueness o Read More