TEST 4 Protein modification Flashcards
What did we cover on Amino-Terminal and Carboxy-terminal modifications?
- Formyl group removed from that initial methionine that initiated bacterial proteins.
- Can remove N-terminal and C-terminal amino acids.
- Amino group of the N-terminal amino acid in many proteins is modified by the addition of N-acetyl group.
What did we cover on cleavage?
- Proteins and hormones synthesized as longer precursors, then broken up.
- Proteases remove sequences.
What did we cover on Phosphorylation?
- Adding phosphate groups to hydroxyl groups on:
- Serine, threonine, and tyrosine
- Phosphorylation is performed by ATP through kinases.
- Role:
- Changes charge = change conformation
- Can act as a on/off switch
- Dephosphorylated by phosphatases.
- Changes charge = change conformation
Types of Glycosylation?
- N-linked - Carbs attached to amide nitrogen of asparagine
- O-linked: Carb chains attached to hydroxyl group of serine and threonine.
- Also can occur on Hydroxylysine and hydroxylproline in collagen.
What did we cover on Isoprenylation
- Farnesylation
- Allows protein to connect to membrane
- Attaches to Cys residue
- irreversible.
What did we cover on GPI
- Amphipathic molecule
- Anchors cell surface proteins to plasma membrane
- Protein cleaved and transferred to the preformed GPI molecule in membrane.
- Can move sideways
What did we cover on N-Myristolyation
- Addition of myristate to N-termini of proteins
- Usually added to glycine, sometimes lysine.
- Benefits:
- Hydrophobicity and guides proteins to membranes
- Usually associated with inner face of plasma membrane
- Requires second signal to hold protein there, acylation
What did we cover on S-palmitoylation
Addition of palmitate to thiol side chain of cysteine
What did we cover on Acetylation?
- Adds acetyl group to terminal amine of lysine.
- Can be done enzymatically or non-enzymatically
- Enzymes:
- Lysine acetyl transferases (KATs) add acetyl groups
- Histone deacetylases (HDAC) remove acetyl groups.
- Enzymes:
- Can be done enzymatically or non-enzymatically
- Reversible
- Works as on/off switch
- Function
- Lysine is + at body pH.
- Decreases stability and unwinds DNA.
- Acetylation increases avaliability of transcription
Structure of proteasome?
- Multi-subunit structure: 26S
- 2 Multi-subunit complexes
- 20S core
- 4 rings
- Outer
- 7a
- Inner
- 7B
- Outer
- 4 rings
- Two 19S caps
- Contain 6 ATPases
- 20S core
- 2 Multi-subunit complexes
Role of Proteosome outer ring?
Control substrate access
Role of Proteosome inner ring?
Have protease activity (chew up protein)
Role of 19S cap?
Regulatory function
Promotes opening of proteasome and providing access for substrates.
Ubiquitin: E1
Ubiquitin activating enzyme, requires ATP
Ubiquitin E2
Ubiquitin Conjugating enzyme (Cys residue grabs ubiquitin)
Ubiquitin E3
Ubiquitin ligase, completes transferal of ubiquitin to protein
Additional Ubiquitin is added where?
To Lysine 48 on the most recently added ubiquitin
How many ubiquitins required for degradation?
4
Disease caused by proteosome inhibition or overwhelming?
Multiple myoloma.
Structure of Ubiquitin?
76 amino acids that end in Glycine
Process of Ubiquitination?
- Ubiquitin added to E1 – requires ATP
- Ubiquitin transferred to Cys residue of E2
- Ubiquitin transferred to lysine on target protein by E3
- Covalent bond between Glycine and the amino group of lysine.
- (ISOPEPTIDE BOND)
- Covalent bond between Glycine and the amino group of lysine.
- Additional Ubiquitin is added to current ubiquitin.
- ATPases in 19S cap recognize ubiquitin and begin unfolding protein.
- Proteases in 20S core cleave it
- Digestion products further degraded by peptidase in cytosol
- Ubiquitin reused.
Where does the Protease in the 20S core cut?
After Hydrophobic, acidic, and basic residues.
What are the other roles of ubiquitin?
- Trasnport to lysosomes
- Signaling
- Regulation of protein function
- Cell division
- Repair of damaged DNA
- Transcription
