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Cell Biology for Bioprocessing
Published in Wei-Shou Hu, Cell Culture Bioprocess Engineering, 2020
Lysosomes are small organelles where the degradation of many cellular materials takes place. Its lumen is a low pH environment (pH ~4.5) and it contains many enzymes that hydrolyze proteins, nucleic acids, and lipids (Panel 2.13). It has proton pumps in the membrane to maintain a low interior pH. It is the site of degradation of both ingested materials and cellular materials that are no longer needed by the cell. Most cellular materials have a finite life span, regardless of whether they are catalyzing chemical reactions or playing structural or mechanical roles. Over time, any cellular material can be oxidized or chemically modified in other ways in some part of its structure. The accumulation of such “damages” may render a protein non-functional. Thus, most proteins and other cellular materials, such as RNAs and lipids, are turned over after a finite period of time. Many of such processes occur in lysosomes. For some proteins, this occurs in proteasomes. Proteasomes are complexes of proteolytic enzymes that are capable of degrading proteins. Proteins that need to be turned over are tagged by ubiquitin and sent to the proteasome for degradation. Lysosomes are not trash cans, but rather more like recycling centers. They play an important role in lipid homeostasis. Lipids taken up from the extracellular environment and other organelles are processed and then redistributed to maintain the proper lipid composition in the membranes of different organelles.
Proteins and Proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Most nonselective protein degradation takes place in the lysosomes, where changes in the supply of nutrients and growth factors can influence the rates of protein breakdown. Proteins enter lysosomes by macroautophagy, which is the enclosure of a volume of the cytoplasm by an intracellular membrane. The rates of lysosomal degradation can vary greatly with cell type and conditions, ranging from <1%/h of total cell protein to 5%–10%/h. The lysosomal degradation of some cytosolic proteins increases in cells deprived of nutrients. It is assumed that the proteins undergoing enhanced degradation are of limited importance for cell viability and can be sacrificed to support the continuing synthesis of key proteins. Short-lived regulatory proteins are degraded in the cytosol by local proteolytic mechanisms. All short-lived proteins are thought to contain recognition signals that mark them for early degradation. One commonly employed method is the selective labeling of targeted proteins by ubiquitin (UB) molecules. Ubiquitin, a protein of 76 amino acids, binds covalently to available lysine residues on target proteins, which are then recognized by proteases. Ubiquitin is a small (8.5 kDa) regulatory protein that has been found in almost all tissues (ubiquitously) of eukaryotic organisms. It was discovered in 1975 and further characterized throughout the 1970s and 1980s. There are four genes in the human genome that produce ubiquitin; UBB, UBC, UBA52, and RPS27A.
Molecular Approaches for Enhancing Abiotic Stress Tolerance in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Sushma Mishra, Dipinte Gupta, Rajiv Ranjan
After discussing the regulatory role of TFs in controlling the expression of stress-responsive genes, it becomes necessary to mention the role of various post-translational modifications (including phosphorylation, methylation, ubiquitination, sumoylation, etc.) involved in the abiotic stress signal transduction pathway. These protein modifications bring about a change in protein conformation and facilitate in transmitting the stress signal through intermediates from the cytosol to nuclei. For example, the activity of AREB1 TF is regulated by ABA-dependent phosphorylation by SNF1-related protein kinase 2 (SnRK2) (Furihata et al., 2006). The stability of various proteins or intermediates of the signaling pathway is often regulated by ubiquitination. The ubiquitination is a process of ubiquitin-mediated degradation. The covalent attachment of ubiquitin to a lysine residue of a target protein can regulate its stability, activity and trafficking, thereby modulating the protein turnover in response to external stimulus (Lyzenga and Stone, 2011).
Exenatide promotes the autophagic function in the diabetic hippocampus: a review
Published in Egyptian Journal of Basic and Applied Sciences, 2022
Eman Mohammed Elsaeed, Ahmed Gamal Abdelghafour Hamad, Omnia S. Erfan, Mona A. El-Shahat, Fathy Abd Elghany Ebrahim
The degradation of cellular components can be achieved by two major systems: the ubiquitin-proteasome system and autophagy. The ubiquitin-proteasome system is concerned with the degradation of the short-lived proteins, as they are tagged by ubiquitin, and recognized and degraded by the proteasome. Autophagy is the process by which eukaryotic cells get rid of intracellular organelles and protein aggregates that cannot be degraded by the proteasome. It degrades long-lived proteins, lipids, and cytoplasmic organelles via a lysosome-driven process [15, 16]. It occurs at a basal level in all cells, and it helps maintain cellular homeostasis. Also, it is proven to have a role in development and disease [17].