why would a change in pH cause a protein to denature?

Answer 1

alterations in pH could change the pattern of ionization of carboxyl and amino groups in the R groups of amino acids, therefore disrupting the pattern of ionic interactions.

Answer 2

By changing pH you would change the H+ ion concentration in the solution. Hence you change the interaction between solute and protein. Ie. increasing hydrogen bonding between solute and protein, hence change the protein conformation and cause denaturation.

Answer 3

several amino acids have acidic or basic side-chains, when protonated or deprotonated these groups may cause the protein conformation to change.