Intracellular proteolysis

Taking into account process integration, i.e. - cultivation and product purification, particle locaHsation is an important issue. Strategies to produce a secreted particle, either by manipulation of its composition or by co-expression of NS protein(s) will be also discussed, since this can lead to an easier purification process and to a decrease in product losses due to intracellular proteolysis. The production of Rotavirus-Hke particles and Bluetongue virus-like particles production will be used as examples to illustrate this point. 

Thus, ATP serves at least three roles in intracellular proteolysis (1) It functions in the tagging of proteins through covalent attachment of ubiquitin, (2) it activates proteases such as La through hydrolysis, and (3) it serves as a positive allosteric effecter of other proteases without being hydrolyzed. The presumed function of this energetic requirement is to ensure the fidelity of protein degradation. It is, after all, nearly as important to cellular function to degrade proteins correctly as it is to synthesize them correctly. 

Bohley, E (1987) Intracellular proteolysis. In Hydrolytic Enzymes (eds Neuberger, A. and Brocklehurst, K.). Elsevier (Biomedical Division), Amsterdam. 

Cai J, Jiang WG, Grant MB, Boulton M. Pigment epithelium-derived factor inhibits angiogenesis via regulated intracellular proteolysis of vascular endothelial growth factor receptor 1. J Biol Chem 2006 281 3604-3613. 

Benzyloxycarbonyl-Val-Ala-Asp(OMe) fluoromethyl ketone (z-VAD-FMK) is a peptide halomethyl ketone used for the inhibition of caspases and related enzymes. Because z-VAD-FMK is neutral, it passes the cell membrane and can inhibit intracellular proteolysis and is useful in understanding the role of caspases and related enzymes in cellular function. See Zhu, H., Fearnhead, H.O., and Cohen, G.M., An ICE-like protease is a common mediator of apoptosis induced by diverse stimuli in human monocytes THP.l cells, FEBS Lett. 374, 303—308, 1995 Mirzoeva, O.K., Yaqoob, P., Knox,... 

Kirschner, M. 1999. Intracellular proteolysis. Trends Cell Biol. 9 M42-M45. 

Katanuma, N. (1989). Possible regulatory mechanisms of intracellular protein catabolism through lysosyme. In Intracellular Proteolysis Mechanisms and Regulations, ed. N. Katanuma E. Kominami, pp. 3-26. Tokyo Japanese Scientific Societies Press. 

Ubiquitin, a 76-residue protein, occurs in every eukaryotic cell and has multiple functions, including the cellular response to stress (Finley and Varshavsky, 1985) and intracellular proteolysis. Ubiquitin is induced in mammalian cells by heat shock and other forms of stress such as DNA damaging agents and isoleucine deprivation (Fomace Jr. et al., 1989). Ascorbic acid might, therefore, be involved in the modulation of cellular stress. 

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