Eukaryotes protein degradation

Lupas, a. N. and Koretke, K. K., Bioinformatic analysis of ClpS, a protein module involved in prokaryotic and eukaryotic protein degradation,... 

In addition to the RC there are two protein complexes, REGajS and REGy, and a single polypeptide chain, PA200, that bind the 20S proteasome and stimulate peptide hydrolysis but not protein degradation. Like the RG, proteasome activators bind the ends of the 20 S proteasome and, importantly, they can form mixed or hybrid 26S proteasomes in which one end of the 20S proteasome is associated with a 19S RC and the other is bound to a proteasome activator [147-150]. This latter property raises the possibility that proteasome activators serve to localize the 26S proteasome within eukaryotic cells. 

Eukaryotic cells degrade proteins within both the cytosol and lysosomes. Lysosomes apparently take up many proteins but have a preference for N-terminal KFERQ132 and also for particular types of glycosylation (Chapter 20). Lysosomes act on many long-lived proteins.1331333 Once within the lysosomes, the proteins are broken down into amino acids with a half-life of 8 minutes. During nutritional deprivation, the rate of uptake of proteins by lysosomes increases markedly. The same is true during certain developmental changes, for example, when a tadpole loses its tail. 

Intracellular protein degradation is not random. Different proteins have quite different half-lives, which are related to specific structural features. Imperfectly folded proteins and polypeptide fragments are frequently degraded most rapidly. In eukaryotes, lyso-somes play a major role in protein degradation. 

Multiprotein complexes are molecular machines. Used by both prokaryotes and eukaryotes, each type of complex efficiently performs a specific biological task. Prominent examples of processes that require the coordinated functioning of large numbers of associated proteins include DNA synthesis, transcription, fatty acid synthesis, and protein degradation. Each element in a multiprotein complex is spatially and temporally positioned to perform a specific operation so that a biological task can be accomplished. In addition to the catalysis of... 

Despite considerable research, the mechanisms of protein turnover are still unclear. However, several aspects of this process are now known. Proteins are degraded by proteolytic enzymes found throughout the cell. These include the cytoplasmic Ca2+-acti-vated calpains and the lysosomal cathepsins. In addition, ubiquina-tion is now believed to have a major role in protein turnover. In ubiquination, illustrated in Figure 15A, several molecules of a small 76-residue eukaryotic protein called ubiquitin are covalently attached to some proteins destined for degradation. Once a pro-... 

Varshavsky and colleagues have also characterized a nonlysosomal protein-degradation pathway in eukaryotic cells, primarily in yeast. In addition to confirming that the N-end rule applies to eukaryotic proteins as well, they identified a 76-amino-acid protein called ubiquitin as one of the major signals for protein degradation. Ubiquitin got its name because it is found in essentially every cell type ever examined. The sequence of ubiquitin is almost identical in yeast and humans,... 

The two primary mechanisms of protein degradation in eukaryotic cells are... 

Methods of protein degradation - Eukaryotic cells have the following two distinct methods for protein degradation ... 

Rogers et (13) have claimed that all rapidly degraded eukaryotic proteins of known... 

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