Lecture 4 - Protein stability Flashcards
What stabilizes proteins?
bonds and interactions
What bonds and interactions stabilize proteins?
- Electrostatic forces
- Hydrogen bonds
- Hydrophobic interactions
- Disulfide bonds
Types of electrostatic forces
- Ionic interaction
- Dipole-dipole interactions (van der Waals)
- Hydrogen bonds
Ionic interactions in proteins are strong, but do not
greatly stabilize proteins
Ion pair or salt bridge
The association of two ionic protein groups of opposite charge
The energy of a typical ion pair is about equal to
two free ions (contribute little stability towards native structure)
Permanent dipole interactions are generally weaker than
ion pair interactions
Permanent dipole moments can be found
between carbonyl and amide groups of the peptide backbone
Energy of dipole interactions and London forces
-0.3 kJ/mol
Hydrogen bonds occur between
a weakly acidic donor group and an acceptor that bears a lone pair
Where are hydrogen bonds located in proteins?
Between N-H and C=O
Energy of hydrogen bonds
12-30 kJ/mol
Hydrogen bonds only weakly stabilize proteins because
unfolded proteins form hydrogen bonds with water, so hydrogen bonds within proteins are only slightly more stable
The strength of hydrogen bonds depends on
the donor-acceptor pair and on their distance
Hydrogen bonds are stronger when
the hydrogen bonds lies in the same direction as the N-H covalent bond
Gibbs free energy changes for the transfer of a hydrocarbon from an aqueous solution to a nonpolar solvent is
negative
Which part of the Gibbs energy equation makes hydrophobic forces so stabilizing?
the entropy component
The hydrophobic effect contribution to protein stability resulting from the burial of nonpolar side chains is approximately
5.6 kJ/mol (per residues, so a 100 residue protein will be 560 kJ/mol)
A hydropathic index of a protein indicates
which residues are in the protein interior and which are in contact with water
Disulfide bonds function to
stabilize the 3D structure of a protein
Disulfide bonds form as
proteins fold to their native conformation
The primary effect of disulfide bonds on protein denaturation is to
decrease the entropy of the unfolded state
