Ubiquitin Structure & Function: Difference between revisions
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Before degradation is complete, the system must ensure that the protein that has been ubiquitinylated is in fact damaged. Enzymes associated with proofreading with either inhibit or stimulate ubiquitin-dependent processes. If the target protein is found to not be damaged, deconjugation of ubiquitin from mono- or polyubiquitinylated proteins will result in order to inhibit any further degradation processes. This reverse reaction is known as a "futile cycle"<ref>Cox, MJ., Haas, AL. and Wilkinson, KD. 1986. Role of ubiquitin conformations in the specificity of protein degradation: iodinated derivatives with altered conformations and activities. Arch Biochem Biophys. 250:00-409</ref>. This is done through the actions of deubiquitinating thiol proteases which recognize the native conformation of ubiquitin and cleave the isopeptide bond located at the carboxyl-terminal G76 of ubiquitin<ref>Wilkinson, KD. 1997. Regulation of ubiquitin-dependent processes by deubiquitinating enzymes. FASEB J. 11:1245-1256</ref>. | Before degradation is complete, the system must ensure that the protein that has been ubiquitinylated is in fact damaged. Enzymes associated with proofreading with either inhibit or stimulate ubiquitin-dependent processes. If the target protein is found to not be damaged, deconjugation of ubiquitin from mono- or polyubiquitinylated proteins will result in order to inhibit any further degradation processes. This reverse reaction is known as a "futile cycle"<ref>Cox, MJ., Haas, AL. and Wilkinson, KD. 1986. Role of ubiquitin conformations in the specificity of protein degradation: iodinated derivatives with altered conformations and activities. Arch Biochem Biophys. 250:00-409</ref>. This is done through the actions of deubiquitinating thiol proteases which recognize the native conformation of ubiquitin and cleave the isopeptide bond located at the carboxyl-terminal G76 of ubiquitin<ref>Wilkinson, KD. 1997. Regulation of ubiquitin-dependent processes by deubiquitinating enzymes. FASEB J. 11:1245-1256</ref>. | ||
=== Conjugate Metabolism === | === Conjugate Metabolism === | ||
If, however, the target protein is found to be | If, however, the target protein is found to be damaged, the ubiquitinylated protein is lead to its degradation by the 26S proteasome<ref>Hochstrasser, M. 1996. Ubiquitin-dependent protein Degradation. Annu Rev Genet. 30: 405-439</ref>. The 26S proteasome is made up of a 20S core and a 19S cap. The targeted protein must be unfolded, deubiquitinylated and translocated through the 19S cap channels and into the proteasome interior. The 20S proteasome than cleaves the polypeptide into short peptides of roughly 7-9 fragment residues. This process is ATP-independent. Cytosolic peptidases then degrades the fragment into its appropriate amino acids. The ubiquitin molecules are returned to the cell where they are reused. | ||
[[Image:proteosome length.png| thumb |left | upright= | [[Image:proteosome length.png| thumb |left | upright=0.75 |Length view of Proteasome]] | ||
[[Image:proteaosome top.png| thumb |right | upright=1.0 |Top view of proteasome]] | [[Image:proteaosome top.png| thumb |right | upright=1.0 |Top view of proteasome]] | ||
=Types of Ubiquitin Conjugates= | =Types of Ubiquitin Conjugates= | ||
There are 3 different types of ubiquitin conjugates known: | |||
1) Ubiquitinylation: | |||
=Diseases= | =Diseases= | ||
<references/> | <references/> | ||
