Ciani - biophysical chem Flashcards
Protein Structures
Primary - Amino Acid residues
Secondary - a-Helix
Tertiary - Polypeptide chain
Quaternary - Assembled sub-units
Right-Handed a-Helix
3.6 residues per turn
Pro breaks helix -> Cannot form backbone H-bond
Highest tendencies to form a-Helix
Met
Glu
Leu
Ala
Lowest tendencies to form a-Helix
Pro
Gly
Tyr
How does Proline confer rigidity to a region of polypeptide chain?
Pro is an immino acid
- no H-bond when in polypeptide chain
Most a-Carbons on amino acid residues have two free rotating bonds
Pro only has one -> Cis/Trans intervonverstion has energy cost
Anti-parallel B-Structures
- Alternating H-bonded and non-H-bonded positions in sheet
- strands run in opposite directions & connect by B-turns
- R-groups on opposite sides of sheet
- Structure may be twisted
B-turns
- Sequence of amino acids in which polypeptide folds back on itself
- Pro residues often present
B-structure twists
- Right-handed twist -> Possibly due to interactions between backbone and amino acid side chain
- Extended polypeptide chain N-structures tend to be twisted for stability and rigidity
Highest tendencies to form B-sheets
Val
Ile
Phe
Lowest tendencies to form B-Sheets
Pro
Asp
Highest tendencies to form B-turns
Pro
Gly
Asp
Lowest tendencies to form B-turns
Met
Val
Ile
Parallel B-structure
- Parallel sheets are less stable, less common
- H-bonds are fewer; less straight than B-sheets
Tertiary Struture
- Secondary motifs pack together to form domains
- always have hydrophobic core
- Can be globular or elongated
- stabilised by non-covalent weak interactions
Timescales of protein folding
a-Helix/B-sheets: 10^-9 - 10^-7 s
molten globule: 10^-6 - 10^-3 s
Annealing: .10^-3 s
Native state: >10^-3 s
