Post Translation Modification

8/4/2019 Post Translation Modification

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Post TranslationModification

So uh, does it not freak you out that there are things that look like worms that move in your entire body at the molecular level? Come on, look at that first picture, it looks like a deadly spirochaette or something… freaky…




Usually protein synthesis yields enzymeprecursors instead of fully functionalenzymes.

Most newly synthesized proteins undergomodifications first before becomingfunctional in different body cells.



Secreted Proteins and Membrane Proteins

• Proteins will either be secreted by the cell• Or become a membrane protein

• All synthesized proteins have signalsequence or signal peptide (of 13-36

predominantly hydrophobic residues)





Proteolytic Cleavage

• Cleavage/removal of an amino acid at apeptide bond.

• Hydrolysis of peptide bonds, unlinkingsome parts of the polypeptide

• Enzyme: Protease

• May lead to protein activation, inhibition ordestruction

• Ex. Preproprotine of insulin• Preproprotine > proinsulin > insuling



Acetylation

• Addition of acetyl group (e.g. methyl) to N-terminus ofpolypeptide or to its lysine residue

• Catalyzing enzyme: acetyltransferase (NATs or HAT)

• 80-90% of human proteins are N-acetylated• Histones are lysine acytelated

• Essential for signalling



Phosphorylation

• Addition of phosphate group to the polypeptide

• Usually to serine>threonine>tyrosine and histidine.

• Catalyzing enzyme: Protein kinase

ATP + protein <——> phosphoprotein + ADP• Most common protein modification, important for

regulatory mechanism.

• ex. Phosphorylation of glycogen synthase and glycogen

phosphorylase in hepatocytes in response to glucagonrelease of pancrease

> Increased hepatic glucose delivery to blood.



Sulfation

• Permanent addition of sulfate group to polypeptide

• Specifically to tyrosine

• Catalyzing enzyme: tyrosylprotein sulfotransferase

(TPST)• Sulfate donor: PAPS

• Adds stability to protein, strengthening protein-proteininteractions

• Secreted proteins and extracellular parts of membraneproteins that pass through golgi apparatus may undergosulfation.





Amidation

• Addition of an amide to C-terminus ofpeptide

• Commonly done to peptide hormones

• Gives structural stability and resistanceto hydrolysis



Ubiquitinylation

• Addition of Ubiquitin via an isopeptide bond (not on mainchain)

• Ubiquitin – small (76 AA) regulatory protein found inalmost all tissues.

• Varying function depending on length

• Addition leads to tagging of protein for destruction bythe proteosome organelle

• Or directed to other parts of the cell.



Glycosylation

• Attachment of sacharrides to polypeptides

• Creates more structural stability or new functions to theprotein.

• Proper anchoring• Cell recognition

• Protein folding

• Types:

• N-glycosylation• O-glyocsylation

• C-mannosylation

• GPI anchor

So uh does it not freak you out that there are things that look like worms that move in your entire body at the molecular level? Come on look at that first picture it looks like a deadly spirochaette or something freaky



END

So uh does it not freak you out that there are things that look like worms that move in your entire body at the molecular level? Come on look at that first picture it looks like a deadly spirochaette or something freaky


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Post Translation Modification