TEST 4 Protein modification

Question 1

What did we cover on Amino-Terminal and Carboxy-terminal modifications?

Answer 1

• 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.

Question 2

What did we cover on cleavage?

Answer 2

• Proteins and hormones synthesized as longer precursors, then broken up.
• Proteases remove sequences.

Question 3

What did we cover on Phosphorylation?

Answer 3

• 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.

Question 4

Types of Glycosylation?

Answer 4

• 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.

Question 5

What did we cover on Isoprenylation

Answer 5

• Farnesylation
  
  • Allows protein to connect to membrane
  • Attaches to Cys residue
  • irreversible.

Question 6

What did we cover on GPI

Answer 6

• Amphipathic molecule
• Anchors cell surface proteins to plasma membrane
• Protein cleaved and transferred to the preformed GPI molecule in membrane.
  
  • Can move sideways

Question 7

What did we cover on N-Myristolyation

Answer 7

• 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

Question 8

What did we cover on S-palmitoylation

Answer 8

Addition of palmitate to thiol side chain of cysteine

Question 9

What did we cover on Acetylation?

Answer 9

• 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.
• Reversible
  
  • Works as on/off switch
• Function
  
  • Lysine is + at body pH.
  • Decreases stability and unwinds DNA.
    
    • Acetylation increases avaliability of transcription

Question 10

Structure of proteasome?

Answer 10

• Multi-subunit structure: 26S
  
  • 2 Multi-subunit complexes
    
    • 20S core
      
      • 4 rings
        
        • Outer
          
          • 7a
        • Inner
          
          • 7B
    • Two 19S caps
      
      • Contain 6 ATPases

Question 11

Role of Proteosome outer ring?

Answer 11

Control substrate access

Question 12

Role of Proteosome inner ring?

Answer 12

Have protease activity (chew up protein)

Question 13

Role of 19S cap?

Answer 13

Regulatory function

Promotes opening of proteasome and providing access for substrates.

Question 14

Ubiquitin: E1

Answer 14

Ubiquitin activating enzyme, requires ATP

Question 15

Ubiquitin E2

Answer 15

Ubiquitin Conjugating enzyme (Cys residue grabs ubiquitin)

Question 16

Ubiquitin E3

Answer 16

Ubiquitin ligase, completes transferal of ubiquitin to protein

Question 17

Additional Ubiquitin is added where?

Answer 17

To Lysine 48 on the most recently added ubiquitin

Question 18

How many ubiquitins required for degradation?

Answer 18

4

Question 19

Disease caused by proteosome inhibition or overwhelming?

Answer 19

Multiple myoloma.

Question 20

Structure of Ubiquitin?

Answer 20

76 amino acids that end in Glycine

Question 21

Process of Ubiquitination?

Answer 21

• 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)
• 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.

Question 22

Where does the Protease in the 20S core cut?

Answer 22

After Hydrophobic, acidic, and basic residues.

Question 23

What are the other roles of ubiquitin?

Answer 23

• Trasnport to lysosomes
• Signaling
• Regulation of protein function
• Cell division
• Repair of damaged DNA
• Transcription