Posttranslational protein phosphorylation

Protein kinases and protein phosphatases catalyze phosphorylation and dephosphorylation of cellular proteins. Posttranslational protein phosphorylation is a major mechanism of signal transduction in eukaryotes it serves as a reversible switch that alters the activity of target proteins as a means to link stimuli to the appropriate cellular response. In this article,... 

Chemical tools have played a central role in elucidating the function of posttranslational protein phosphorylation. Kinase and phosphatase inhibitors have played a major role in the study of protein phosphorylation because they allow rapid, reversible inactivation of the target in meaningful contexts (cells and organisms) to study its biologic function. Chemical tools have also helped identify the direct substrates of individual kinases and phosphatases, and conversely, they have helped identify which kinase is responsible for phosphorylating a particular phosphoprotein. Here I will focus on chemical tools developed for protein kinases several reviews discuss chemical tools for protein phosphatases (15, 16). 

The transcriptional activity of NRs is also modulated by various posttranslational modifications of the receptors themselves or of their coregulatory proteins. Phosphorylation, as well as several other types of modification, such as acetylation, SUMOylation, ubiquitinylation, and methylation, has been reported to modulate the functions of NRs, potentially constituting an important cellular integration mechanism. In addition to the modifications of the receptors themselves, such modifications have been reported for their coactivators and corepressors. Therefore, these different modes of regulation reveal an unexpected complexity of the dynamics of NR-mediated transcription. 

Phosphorylation is the reversible process of introducing a phosphate group onto a protein. Phosphorylation occurs on the hydroxyamino acids serine and threonine or on tyrosine residues targeted by Ser/Thr kinases and tyrosine kinases respectively. Dephosphorylation is catalyzed by phosphatases. Phosphorylation is a key mechanism for rapid posttranslational modulation of protein function. It is widely exploited in cellular processes to control various aspects of cell signaling, cell proliferation, cell differentiation, cell survival, cell metabolism, cell motility, and gene transcription. 

In summary, there is evidence that suggests that the activities of some stress-70 proteins may be modulated in vivo by protein phosphorylation or ADP-ribosylation. However, at this time, there is no case in which a modifying enzyme has been purified and demonstrated to modify a target stress-70 protein in vitro. Hence, the question of whether there is functionally significant posttranslational modification of stress-70 proteins remains an open question at this time. 

Phosphorylation. Phosphorylation is a posttranslational modification that is reflected in close to 30% of eukaryotic gene products and almost 2% of the human genome-encoded protein kinases. Protein phosphorylation plays an essential role in intercellular communication during development, in physiological responses and homeostasis, and in the functioning of the nervous and immune systems. Reversible phosphorylation regulates many diverse... 

Although the physiologic roles of this novel posttranslational modification need to be evaluated, serine pyrophosphorylation likely expands on the already well-defined roles of canonical protein phosphorylation in modifying protein conformation, regulating catalytic activity, determining protein localization, or altering protein-protein interactions. Experiments assessing these possibilities are currently underway. 

In planning a protein production project, there are a number of factors to be taken into consideration. What is the intended final use of the protein (enzymatic assays, antibody generation, crystallography, etc.) Does the protein need to be active and correctly folded Is the protein expected to have posttranslational modifications (phosphorylation, glycosylation, site-specific proteolysis, etc.) How much protein is going to be needed Will any fusions need to be removed Is the protein expected to incorporate cofactors Is the protein expected to... 

The reversible phosphorylation of proteins is one of the most widespread posttranslational modifications, mediating responses to internal and external signals in a variety of cellular processes [1-3]. In eukaryotes 30-70 % of all proteins are phosphorylated on tyrosine (Tyr), threonine (Thr), and/or serine (Ser) residues [4-6]. Protein phosphorylation is catalyzed by protein kinases, which transfer the y-phosphate of ATP to a hydroxyl side chain, resulting in the formation of a phosphate monoester. Protein phosphatases hydrolyze these phosphate monoesters and make protein phosphorylation a reversible modification [4]. 

In contrast to the biosynthetic systems for catecholamines and serotonin discussed earlier, there appear to be no posttranslational modifications such as protein phosphorylation or proteolytic activation that regulate the catalytic state of choline acetyltransferase. A more detailed discussion of acetylcholine synthesis may be found in Blusztajn and Wurtman (1983). 

Protein phosphorylation is a pervasive posttranslational modification in cells. It is reversible and can dramatically affect the activity of a modified protein. Protein phosphorylation is one of the most important mechanisms used for signal transduction by cells. In prokaryotic cells, the best-known reversible protein phosphorylations occur on histidine and aspartate in eukaryotes the best-known occur on the hydroxyl groups of serine, threonine, and tyrosine, although histidine can also be phosphorylated (Fig. 3.9). Other reversible modifications also occur, such as the acetylation of lysine residues in histone proteins. 

Posttranslational modification profiling Specific biochemical methods are used to identify the abundance of targets with specific posttranslational modifications (such as phosphorylated proteins) (Zheng and Chan, 2002). Monitoring protein phosphorylations is particularly important in mapping the intracellular signaling network... 

Phosphorylation, or the attachment of a phosphate group to amino acid side chains, is one of the most abundant posttranslational modifications (PTMs) of proteins. Phosphorylation reactions are mediated by phosphotransferase enzymes, termed kinases, with ATP as the typical source of the transferred phosphoryl group. Ser, Thr, and Tyr are the most commonly phosphorylated residues in eukaryotes, while His and Asp phosphorylation has also been observed, predominantly in prokaryotes. Protein activity, localization, and structure as well as protein-protein interactions are all affected by protein phosphorylation [1, 2]. As kinases play integral roles in cellular signaling, dysregulated kinase function has emerged as a driver for many different disease states, including... 

Protein phosphorylation is one of the most important posttranslational modifications for cellular functions and signal transduction. As the phosphorylation state of a protein is controlled by the kinase and the phosphatase, modulators of kinases and phosphatases are valuable tools to study their functions. Compared to the large amount of kinase modulators, the development of phosphatase modulators is still limited and challenging. Over the years, protein phosphatases have been notoriously difficult to study. 

Lane, P., Hao, G., and Gross, S.S. (2001). S-nitrosylation is emerging as a specific and fundamental posttranslational protein modification head-to-head comparison with O-phosphorylation. Sci. STKE. 2001, REl. 

Reversible phosphorylation requiring both a kinase and a phosphatase is implicated in the control of many cellular process. Generally, a phosphate group is linked to serine or threonine and also to tyrosine residues in proteins. Phosphorylation in enzyme molecules generally leads to a modification of the catalytic activity (see review, England, 1980). Other modifications have been also described such as methylations and ADP-ribosylation. Formation of disulfide bonds is also a posttranslational process. 

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