Protein Folding and PostTranslational Modification

1
Protein Folding and Post-Translational
Modification

• Lessons in protein structure with physical models
• -Tom Mellon Brandon Poe

2
Review

• Secondary Structures
• a-helix
• b-sheet
• Teriary structure
• Quaternary structure

3
I lied

• The polypeptide translated from the INS gene is
  110 a.a. long
• The a-chain is 21 a.a. long and the b-chain is 30
  a.a. long
• Does that add up?
• A 24 a.a. signal peptide is cleaved upon entry
  into the ER
• A 35 a.a. chain is cleaved from between the two
  chains

4
Signal Peptides

• A protein that is destined for the cell surface
  or to be secreted, is processed in the ER

5
Proteolytic cleavage of peptides

• Removing initial methionines
• Insulin
• Pancreatic enzymes

6

• New polypeptide has entered the lumen of the ER
• Signal peptide cleaved by SPase
• Proinsulin and enzymes go through Golgi
• Both are packaged into secretory vesicle
• C-peptide is cleaved out of peptide in vesicle
  before secretion