|
| ||
|
|
||
Cellular Life (cellular + life)
Selected AbstractsThe ubiquitin-proteasome system and its role in ethanol-induced disordersADDICTION BIOLOGY, Issue 1 2002Terrence M. Donohue Jr The levels of these proteins are controlled by their rates of degradation. Similarly, protein catabolism plays a crucial role in prolonging cellular life by destroying damaged proteins that are potentially cytotoxic. A major player in these catabolic reactions is the ubiquitin-proteasome system, a novel proteolytic system that has become the primary proteolytic pathway in eukaryotic cells. Ubiquitin-mediated proteolysis is now regarded as the major pathway by which most intracellular proteins are destroyed. Equally important, from a toxicological standpoint, is that the ubiquitin-proteasome system is also widely considered to be a cellular defense mechanism, since it is involved in the removal of damaged proteins generated by adduct formation and oxidative stress. This review describes the history and the components of the ubiquitin-proteasome system, its regulation and its role in pathological states, with the major emphasis on ethanol-induced organ injury. The available literature cited here deals mainly with the effects of ethanol consumption on the ubiquitin-proteasome pathway in the liver. However, since this proteolytic system is an essential pathway in all cells it is an attractive experimental model and therapeutic target in extrahepatic organs such as the brain and heart that are also affected by excessive alcohol consumption. [source] From ancient genes to modern communities: the cellular stress response and the evolution of plant strategiesFUNCTIONAL ECOLOGY, Issue 5 2005S. PIERCE Summary 1Two major plant strategy theories attempt to explain how phenotype determines community structure. Crucially, CSR plant strategy theory suggests that stress and sporadic resource availability favour conservative phenotypes, whereas the resource-ratio hypothesis views the spatial heterogeneity of resources as selecting for optimal foraging in chronically unproductive habitats. Which view is most realistic? 2The ecophysiology literature demonstrates that stress is comprised of two processes: (1) limitation of resource supply to metabolism; and (2) damage to biomembranes, proteins and genetic material (chronic stress). Thus stress is defined mechanistically as the suboptimal performance of metabolism. 3Adaptations to limitation buffer metabolism against variability in external resource supply; internal storage pools are more consistent. Chronic stress elicits the same ancient cellular stress response in all cellular life: investment in stress metabolites that preserve the integrity and compartmentalization of metabolic components in concert with molecular damage-repair mechanisms. 4The cellular stress response was augmented by morphological innovations during the Silurian,Devonian terrestrial radiation, during which nutrient limitation appears to have been a principal selection pressure (sensu CSR theory). 5The modern stress,tolerator syndrome is conservative and supports metabolism in limiting or fluctuating environmental conditions: standing resource pools with high investment/maintenance costs impose high internal diffusion resistances and limit inherent growth rate (sensu CSR theory). 6The resource-ratio hypothesis cannot account for the cellular stress response or the crucial role of ombrotrophy in primary succession. CSR theory agrees with current understanding of the cellular stress response, terrestrial radiation and modern adaptations recorded in chronically unproductive habitats, and is applicable as CSR classification. [source] Broadening the mission of an RNA enzymeJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2009Michael C. Marvin Abstract The "RNA World" hypothesis suggests that life developed from RNA enzymes termed ribozymes, which carry out reactions without assistance from proteins. Ribonuclease (RNase) P is one ribozyme that appears to have adapted these origins to modern cellular life by adding protein to the RNA core in order to broaden the potential functions. This RNA-protein complex plays diverse roles in processing RNA, but its best-understood reaction is pre-tRNA maturation, resulting in mature 5' ends of tRNAs. The core catalytic activity resides in the RNA subunit of almost all RNase P enzymes but broader substrate tolerance is required for recognizing not only the diverse sequences of tRNAs, but also additional cellular RNA substrates. This broader substrate tolerance is provided by the addition of protein to the RNA core and allows RNase P to selectively recognize different RNAs, and possibly ribonucleoprotein (RNP) substrates. Thus, increased protein content correlated with evolution from bacteria to eukaryotes has further enhanced substrate potential enabling the enzyme to function in a complex cellular environment. J. Cell. Biochem. 108: 1244,1251, 2009. © 2009 Wiley-Liss, Inc. [source] Origin and evolution of the protein-repairing enzymes methionine sulphoxide reductasesBIOLOGICAL REVIEWS, Issue 3 2008Xing-Hai Zhang Abstract The majority of extant life forms thrive in an O2 -rich environment, which unavoidably induces the production of reactive oxygen species (ROS) during cellular activities. ROS readily oxidize methionine (Met) residues in proteins/peptides to form methionine sulphoxide [Met(O)] that can lead to impaired protein function. Two methionine sulphoxide reductases, MsrA and MsrB, catalyse the reduction of the S and R epimers, respectively, of Met(O) in proteins to Met. The Msr system has two known functions in protecting cells against oxidative damage. The first is to repair proteins that have lost activity due to Met oxidation and the second is to function as part of a scavenger system to remove ROS through the reversible oxidation/reduction of Met residues in proteins. Bacterial, plant and animal cells lacking MsrA are known to be more sensitive to oxidative stress. The Msr system is considered an important cellular defence mechanism to protect against oxidative stress and may be involved in ageing/senescence. MsrA is present in all known eukaryotes and eubacteria and a majority of archaea, reflecting its essential role in cellular life. MsrB is found in all eukaryotes and the majority of eubacteria and archaea but is absent in some eubacteria and archaea, which may imply a less important role of MsrB compared to MsrA. MsrA and MsrB share no sequence or structure homology, and therefore probably emerged as a result of independent evolutionary events. The fact that some archaea lack msr genes raises the question of how these archaea cope with oxidative damage to proteins and consequently of the significance of msr evolution in oxic eukaryotes dealing with oxidative stress. Our best hypothesis is that the presence of ROS-destroying enzymes such as peroxiredoxins and a lower dissolved O2 concentration in those msr -lacking organisms grown at high temperatures might account for the successful survival of these organisms under oxidative stress. [source] | ||||||||||