Post-translational modifications - week 2 Flashcards
What is post translational modification?
the modification of selected residues in a protein after it has been made but not as part of synthesis
Where do some posttranslational modifications take place?
ont he nascent chain
name for examples of PTM
- acetylation
- hydroxylation
- glycosylation
- phosphorylation
What is acetylation?
- addition of acetyl group
- mostly at N-terminal
- only found in eukaryotes - not in mitochondria and chloroplasts
can lysine residues be acetylated within the protein?
yes - gamma amino group
How may cytoplasmic proteins are acetylated?
around 60 to 90%
what does acetylation involve?
transfer of acetyl group from cofactor acetyl coenzyme A
- done by acetyltransferase enzyme
What proteins do most often become N-Terminally acetylated?
structural proteins such as keratin
What does N-term acetylation do?
- protects proteins form degradation by amino peptidases
- increases half-life of proteins form seconds to hours or days
Can histones be acetylated?
yes,
- lysine residues in histone proteins are often acetylated
- associated with histones born to transcriptionally active DNA
What is result of histone acetylation?
- reduces net positive charge between histones and DNA leading to more open confirmation and more transcriptional activity
What do histone deacytalases (HDACs) do?
remove modification leading to a closed nucleosome conformation with no transcriptional activity
What is hydroxylation?
- the addition of an OH group
What residues can be hydroxylated?
proline -> hydroxyproline
lysine -> hydroxylysine
What does hydroxylation do?
- hydroxyl groups can form hydrogen bonds with water molecules
- hydroxylation of organic compounds converts hydrophobic molecules into hydrophilic molecules
What is a major component of collagen?
hydroxyproline (hydroxylysiine also present)
What does hydropproline do?
involved in H bonding within collagen fibre which is key for its structural stability
What do you call the enzyme that converts porcine to hydroxyproline ?
prolyl hydroxylase
What is required by prolyl hydroxylate as a cofactor?
ascorbic acid (vitamin C)
What is the connection between hydroxylation and collagen?
- collagen sequences has GXY repeat
- porcine is often found in X position
- 15-30% of proline is in hydroxyproline form, normally in the Y position
What is glycosylation?
the attachment of sugar molecules to specific residues in proteins
Where does glycosylation take place?
- only in eukaryotes
- in lumen of ER and in Golgi
What does sugar make proteins?
more soluble
What is the effect of some glycosylations to proteins?
makes them prone to degradation
