Post Translational Modifications Flashcards
Give 3 ways in which the range of protein function can be extended (through post translational modification).
- Phosphorylation (to activate or deactivate it)
- Attaching cofactors (which enhances enzyme activity)
- Addition of hydrophobic groups to change the localisation of the protein
What does adding a hydrophobic group do to protein localisation?
It causes the protein to localise to the plasma membrane.
Where do most molecules start in the cell and where do hydrophobic sex hormones and retinoids go?
Most start at the cell membrane whereas sex hormones and retinoids bypass the cell membrane and go straight to the nucleus
Give 4 ways in which the localisation of the protein can be altered (e.g. which molecules are added to the protein).
- Palmitolylation (adding palmitate group with G(alpha)s subunit to activate adenyl cyclase
- Myristoylation (adding myristate group) which has a G(alpha)i subunit which inhibits adenyl cyclase
- Prenylation
- Glypiation- adds a GPI anchor to anchor the protein to the plasma membrane
What is contact dependent signalling?
Where the signalling molecule remains bound to the signalling cell surface and only influences cells which come into contact with it.
What is retinal and what does it do?
It is a cofactor/ chromophore for the visual receptor rhodopsin (it is the molecule which receives the photon of light).It forms part of the rhodopsin receptor.
What is a Rab protein?
A type of Ras, a monomeric G protein that regulates vesicle trafficking and are anchored to membranes via prenyl groups
How does prenylation occur?
Farnesyl transferase, Caax protease and geranylgeranyl transferase transfer either farnesyl or geranyl geranyl moiety to C terminal cysteine residies. The Caax protease removes AAX residues
How does glypiation occur?
A GPI (glycosylphosphatidylinositol) anchor is added to anchor the protein to the plasma membrane.
What can N terminus acetylation of a protein be a signal for?
It can be a signal for protein degradation
What is the common donor for lysine acetylation? (What acts as the acetyl group donor?)
Acetyl Co A
What effect does glycosylation (addition of glycan group) have on protein folding and stability?
Can enhance protein folding and stability.
What function other than enhancing protein folding and stability can glycosylation have?
It can play a role in cell-cell adhesion.
What does S-nitrosylation regulate?
It regulates cell signalling and apoptosis through down regulation of caspases.
What do caspases do?
They stimulate apoptosis and programmed cell death.
In a hydroxyl sidechain, which three amino acids usually get phosphorylated?
Serine, threonine and tyrosine.
What does phosphorylation do to the hydrophobicity of a molecule?
It converts non polar amino acid side chains into hydrophilic polar group in the molecule.
