Answer
Hydroxylation of proline and methylation of histidine would NOT significantly affect the pI. However, acetylation of Lys, carboxylation of Glu and phosphorylation of Ser will LOWER the pI.
Work Step by Step
Modifications affect the charge on the amino acid, which will then affect the pH where the amino acid will be neutral. For example, phosphorylating Ser lowers the pH range needed for neutrality, which consequently lowers the pI.
