metabolisme protein (kiss of death)

8/17/2019 Metabolisme Protein (Kiss of Death)

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Kiss of Death

Sry Suryani W


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• Defnition o Ubiquitin

• Ubiquitin: A small but extremely important protein thatacts the "kiss of death" to other proteins.

• Ubiquitin consists of only 7 amino acids.

• !n the normal course of eents# proteins are inactiated bythe attachment of ubiquitin to them# a process calledubiquitination

• Ubiquitin acts as a ta$ by %hich the protein&transportmachinery ferries a protein to the proteasome forde$radation.

• Anta$oni'in$ this process are en'ymes that remoe

ubiquitin from proteins.• Ubiquitin is appropriately named since it is ubiquitous and

is present in irtually all types of cells. !t is also one of themost hi$hly consered (least chan$ed) proteins durin$

eolution.• *he amino acid sequence of ubiquitin is identical in all

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• *he cell functions as a hi$hly&e,cientcheckin$ station %here proteins are builtup and broken do%n at a rapid rate.

• *he de$radation is not indiscriminate buttakes place throu$h a process that iscontrolled in detail so that the proteinsto be broken do%n at any $ien momentare $ien a molecular label.


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• *his label has been called a "kiss ofdeath." *he labelled proteins are then fed

into the cells- "%aste disposers"# the socalled proteasomes# %here they arechopped into small pieces and destroyed.

•

*he kiss&of&death is ubiquitin. !t fastensto the protein to be destroyed#accompanies it to the proteasome %hereit is reco$nised as the key in a lock# and

si$nals that a protein is on the %ay fordisassembly. Shortly before the protein issquee'ed into the proteasome# itsubiquitin label is disconnected for re&use.

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• !n //0# Aaron 1iechanoer andAram 2ershko of the *echnion !srael!nstitute of *echnolo$y in 2aifa# !sraeland !r%in 3ose of the Uniersity of1alifornia# !rine# USA shared the4obel 5ri'e in 1hemistry "for the

discoery of ubiquitin&mediatedprotein de$radation."


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• Proteasome: A protein de$radation"machine" %ithin the cell that candi$est a ariety of proteins into short

polypeptides and amino acids.

• *he proteasome is itself made up ofproteins. !t requires A*5 to %ork. !t is

hollo% and has openin$s at both endsto allo% entry of the protein to bedi$ested.

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• A human cell contains about 6/#///proteasomes. *hese barrel&formedstructures can break do%n practically

all proteins to 7&&amino&acid&lon$peptides.

• *he actie surface of the proteasome

is %ithin the barrel %here it is shieldedfrom the rest of the cell.

•


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• *he only %ay in to the actie surfaceis ia the "lock"# %hich reco$nisesproteins ta$$ed %ith ubiquitin#

denatures these proteins and admitsthem to the barrel for disassembly#once the ubiquitin label has been

remoed.• *he peptides formed are released

from the other end of the proteasome.


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• 5roteasomes di$est mainlyendo$enous proteins# thosesynthesi'ed %ithin the cell# as

opposed to extracellular proteins suchas the proteins in blood plasma.

• *he di$estion of protein remoes

excess en'ymes and transcriptionfactors and supplies amino acids forne% protein synthesis.

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metabolisme protein (kiss of death)

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