Gluten protein in the diet is broken down in the body to various peptides. One of these peptides is gluten exorphin B4, a peptide with opioid properties possibly associated with autism and schizophrenia. a. The amino acid sequence of gluten exorphin B4 is YGGW. Using simple stick figures, show a titration experiment of the peptide from low to high pH. Clearly indicate the pKa values of the ionizable groups, and the net charge of the different species.
b. What is the isoelectric point of gluten exorphin B4?
c. Gluten exorphins can be detected in the urine (pH ~ 6) of autistic children. Draw the structure of gluten exorphin B4 at pH 6.0. Show correct stereochemistry around the alpha carbon.
d. Gluten exorphin B4 binds the opiate receptor in the brain with KD = 4.1 μM at physiological temperature (37 °C). What is the change in free energy for the binding reaction?