Ionic Interactions 2. Hydrophobic Interactions 3. Hydrogen Bonds Noncovalent interactions are individually weak but collectively strong. There are three principle kinds of noncovalent forces. At any given pH , proteins have charged groups that may participate in binding them to each other or to other types of molecules.
Ionic interactions are highly sensitive to changes in pH .
Link to example showing how all serum proteins become negatively-charged at a pH of 8.6. Increasing salt concentration reduces the strength of ionic binding by providing competing ions for the charged residues. For this reason, most of the nonpolar residues in globular proteins are directed toward the interior of the molecule whereas such polar groups as aspartic acid and lysine are on the surface exposed to the solvent. The strength of hydrophobic interactions is not appreciably affected by changes in pH or in salt concentration. Noncovalent interactions are individually weak but collectively strong.