Physical modifications are reversible
Give an example of protein oxidation
Disulphide bond formation
Hydrogen bond formation
Where are proteins with oxidated modifications are nearly universally found where?
Outside the cell
I.e. Oxidative environments
What is so useful about disulphide bonds?
They're heat stable
They're protease resitant
They're structurally resilient
Where do oxidation reactions occur?
Disulphide bonds assist in recovery from denaturation
In Maristoylation, what is added?
Describe the substrate added in Myristoylation
Saturated & hydrophobic
Unsaturated & hydrophilic
What is the point of Myristoylation?
It polarises a protein
It binds a protein to a membrane
It binds two ends of a protein together
What sequence is the Myristoylation substrated added to?
The protein that performs Myristoylation is N-Myristoyl transferase
How is the Myristoylation substrate added?
First the phenylalinine is removed
First the methionine is removed
First the tyrosine is removed
Then the substrate is added to the glycine
Then the substrate is added to the leucine
Then the substrate is added to the isoleucine
Prenylation is the addition of ketones
Name the two substrates most often added in prenylation
Where does prenylation occur?
In a CAAX box (where A should be Alanine, but anything small and hydrophobic will do)
In a FAAX box (where A should be Isoleucine, but anything small and hydrophobic will do)
In a CAAT box (where A should be Alanine, but anything small and hydrophobic will do)
In prenylation, the X of the sequence must be the terminal aa of the chain
Put the following in order
A- The COOH group is modified to a methyl group to make it uncharged
B- The substrate is added to the cystine
C- The last three aa are removed
Prenylation is done to proteins destined for the cytoplasm
Name the types of glycosylation
Glycosylation is the addition of carbohydrate chains
What is the site of N-linked glycosylation?
The Asn in an NX(S/T)
The Phe in an FX(S/T)
The Gly in a GX(S/T)
What is the residue that is attached to the amino acid?
What residues are on the tips of the branches?
If the branches end with mannose, what is the process called?
High-mannose Biantennary N-glycosylation
Why are 3 glucose added to the sugar complex in the golgi?
So they can be removed as markers for protein folding and transport
So the Golgi knows they're bound for the membrane
So the Golgi can degrade the protein as faulty
Why is it called High-Mannose Biantennary N-Glycosylation?
Because one of the three branches is removed, giving two 'antenna'
Because another branch is formed off the first one, giving two 'antenna'
Because proteins with this type of glycosylation act as receptor proteins with two antenna
Once the Biantennary complex has been formed, what happens next?
Mannose is removed
Addition of N-acetyl neuraminic acids
Addition of glucose
Removal of N-acetyl glucosamine
Addition of a fucose to the GlcNac bound to the amino acid
Why the complicated process of adding and removing sugars?
It adds a date stamp to the cell- over time the NeuAc's fall off, which signals the protein for degredation
It adds a transport signal- depending on what is added or removed, proteins are directed to different areas by carrier proteins
It's quality control- the contortions required to add and remove all the sugars mean that the protein has folded properly
The HIV virus can use glycosylation to hide from the immune system
Why is N-linked glycosylation potentially dangerous?
Because the immune system is programmed to ignore it, viral coat proteins can use it to hide the virus
Because NeuAc's can be toxic in high concentrations
Because the removal of mannose can cause the protein to misfold
HIV1-gp120 has many N-X-(T/S) sequences to be glycosylated
Where does HIV1-gp120 bind?
How does the HIV virus invade the lyphocyte?
It's only glycosylated on a very small binding site
It's only not glycosylated on a very small binding site
Which allows it to bind and invade