Hello Friends
I will discuss proteosome today.
The function of lysosome organelle is to beakdown potein and other cellular and extracellular components. The pathway which is independent of lysosome is called ubiquitin proteosome pathway as it does not use lysosome for the above function.The pathway is ATP dependent.
Ubiquitin is a polypeptide which can either exist freely in cytoplasm or covalently conjugated with protein.
The molecule to be degraded is ligated to ubiquitin molecule and then it is recognised by proteosome for degradation.
Binding of ubiquitin to target protein is multistep process and is post translational modification.
Glycine is present at C terminal(carbxy) of Ubiuitin and it normally attch to NH2 group of lysine of target protein so an isopeptide bond is formed.
After ubiquitinisation they are identified by 26S proteosome.
For identification by proteosome at least 4 ubiquitin are required.
The 26S proteosome is composed of 19S and 20S subunits.
The 19S subunits have ATPase activity and identify ubiquitin tail attached to target. It forms the upper and lower subunits.
The 20S subunit are central to 19S subunits.
20S is barrel shaped made of 4 ring shaped layers and each layer has 7 protein.
Central 2 layer are called beta and peripheral are called alpha rings or layers.
The beta have catalytic sites and involved in degradation.
when 19S identify target, the alpha unit open and make ubiquitinised target to enter into core subunit beta and then the alpha closed.
The target is breakdown into peptides inside proteosome and released. Point to remember is the proteosome do not degrade target into aminoacid rather it breaks into peptides.
In cytoplasm the other enzymes(peptidases) act on these peptides and degrade target completely into aminoacids.
Ubiquitin tail is identified by deubiuitinating enzyme and cleaved into ubiquitin molecules to be reused.
Hope this will help you all. See you all with next topic.
Thankyou for reading.
I will discuss proteosome today.
The function of lysosome organelle is to beakdown potein and other cellular and extracellular components. The pathway which is independent of lysosome is called ubiquitin proteosome pathway as it does not use lysosome for the above function.The pathway is ATP dependent.
Ubiquitin is a polypeptide which can either exist freely in cytoplasm or covalently conjugated with protein.
The molecule to be degraded is ligated to ubiquitin molecule and then it is recognised by proteosome for degradation.
Binding of ubiquitin to target protein is multistep process and is post translational modification.
Glycine is present at C terminal(carbxy) of Ubiuitin and it normally attch to NH2 group of lysine of target protein so an isopeptide bond is formed.
After ubiquitinisation they are identified by 26S proteosome.
For identification by proteosome at least 4 ubiquitin are required.
The 26S proteosome is composed of 19S and 20S subunits.
The 19S subunits have ATPase activity and identify ubiquitin tail attached to target. It forms the upper and lower subunits.
The 20S subunit are central to 19S subunits.
20S is barrel shaped made of 4 ring shaped layers and each layer has 7 protein.
Central 2 layer are called beta and peripheral are called alpha rings or layers.
The beta have catalytic sites and involved in degradation.
when 19S identify target, the alpha unit open and make ubiquitinised target to enter into core subunit beta and then the alpha closed.
The target is breakdown into peptides inside proteosome and released. Point to remember is the proteosome do not degrade target into aminoacid rather it breaks into peptides.
In cytoplasm the other enzymes(peptidases) act on these peptides and degrade target completely into aminoacids.
Ubiquitin tail is identified by deubiuitinating enzyme and cleaved into ubiquitin molecules to be reused.
Hope this will help you all. See you all with next topic.
Thankyou for reading.
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