5. (12 Points) We learned that larger proteins may have specific domains that contribute to catalytic...
5. (12 Points) We learned that larger proteins may have specific domains that contribute to catalytic activity of an enzyme. In most cases, the independent isolated domains can be separated and will remain folded in solution. In the context of a full length protein, these domains are interconnected within the protein by flexible loops. An example enzyme protein (EX-FL) has a peptide bond cleaved between two residues to produce two fragments, a peptide fragment (20 residues in length, EX-pep) and a protein fragment (104 residues in length, EX-protein). Upon mixing equimolar concentrations of the peptide and protein, these protein fragments assemble into a 3D conformation similar to the wild type and are stabilized by noncovalent forces. In solution, the peptide fragment alone is mostly unfolded while the protein fragment alone has 4 original disulfide bonds and will unfold if the disulfide bonds are "scrambled" or rearranged. Below is a graph of the inactivation and disulfide interchange of the full length EX-FL enzyme (open circles) and the cleaved protein fragment EX-protein (closed circles) facilitated by protein disulfide isomerase. At T=80min, 1.3 equivalents of the peptide fragment EX-pep were added to the EX-protein (shown by arrow). Explain the results. 00 Percent of activity 0 30 60 90 150 180 210 120 Time mini