At pH $1,$ histidine will have a net charge of $$ and will $$ when placed in an electric field.

Most globular proteins denature and lose their activity when briefly heated to $65C.$ However, globular proteins that contain multiple disulfide bonds often require longer heat exposure at higher temperatures to denature them. One such protein is bovine pancreatic trypsin inhibitor $($BPTI$).$ BPTI has $58$ amino acid residues in a single peptide chain and contains three disulfide bonds. After cooling a solution of heat denatured BPTI, the protein regains its activity.

What is the molecular basis for this property of BPTI?

Disulfide bonds lower the optimal temperature of the reaction BPTI participates in$.$

Disulfide bonds make BPTI more rigid at high temperatures than low temperatures.

Disulfide bonds protect BPTI from peptide bond hydrolysis during heating.

Disulfide bonds prevent the complete unfolding of BPTI at high temperatures.