Lecture 5

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OK. What does this all have to do with enzymes?

Anfinsen’s experiment

Took a protein (AP) & forced it to unfold

- Protein lost activityTherefore:______________________________Allowed protein to recover

- Over time, activity returned

Therefore:______________________________

What does a protein need in order to fold?

Protein folding information contained in

primary amino acid

sequence!OK. But how does amino acid sequence

“fold?”

Peptide bond is planar…

…but not bonds on either side!

Rotation of bonds around peptide bond

Peptide backbone rotation

“Folding” proteins

Amino acids have different propertiesDifferent preferred Psi and Phi anglesBonds can rotate and pivot

Secondary structure

3D structure

H-bonds between C=O & N-H

C=O & N-H of peptide bonds

Close together in primary structure

Folding into secondary structures

Bond rotation causes secondary structurea-helix

b-sheet

Bends, Loops, Disordered

The a-helix: Annotate

Different parameters define a-helix

b-Sheet: Annotate

b-Sheets

Sheets can be twisted

Bends / Loops

Bends or Loops: ImportantStructured/Unstructured

Tertiary structrue

Bring secondary structure elements together

Hydrophobic interactions important

Unstructured regions important

The a-helix

Arrangement of side chains important

Tertiary structure

Tertiary structrue

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