Protein Modification

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What are the different types of Protein modification?

1. Acetylation

involves Acetyl Coenzyme A and Nth terminal of Protein.

Dont occur in eukaryotes, mitochondria or chloroplast.

Occurs in cytoplasm.

Reduces chances of degradation and extends life span.

2. Hydroxylation

addition of OH group to Lysine or Serine.

Gly-Xaa-Yaa is a general structure. Yaa being 4-Hydroxypropline, formation of which requires Prolyl Hydroxylase, which requires Ascorbic acid.

3. Glycosalation

addition of sugar to specific amino acids

There are 2 types:

N-glycosalation- where sugar attaches to Nitrogen on Asarganine - switches on/off mechanism

O-glycosalation- where sugar attaches to Oxygen on Serine or Threonine - increasing solubility

4. Phosphorylation

addition of phosphoryl group on specific amino acid, for enzyme regulation

added to Oxygen on Serine, Threonine and Tyrosine, with the help of Protein Kinases and removed by Protein phosphotases.

5. Cleavage

Hydrolysis of peptide bonds resulting in cleavage.

Performed by Proteases:

Carboxypeptidase A - Metalloproteases -Zn cleaved last C-terminal

Chymotrypsin - cleaves C-terminal of hydrophobic residue. Serine in active site

HIV Proteases - cleaves out of large chain protein formed from virus genetics material

What are Preproproteins and proproteins?

Some polypeptides are longer than native length because added parts move protein to compartments, help protein folding and makes prontein inactive. needs to be cleaves to be active eg. chymotrypsin

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