In order to ensure your newly designed peptide vaccine does not cause cell growth upon binding, you must substitute the Threonine residue at position 5. What amino acid would you replace it with, bearing in mind that the peptide should still be similar enough to bind to the gp100 protein in the surface of melanocytes. Explain your choice

1. You plan to synthesize a peptide to be used as a vaccine to treat melanoma, a particularly aggressive form of skin cancer. Normally, gp100, a protein on the surface of melanocytes, activates cell growth when it is bound by its ligand. Activation of the growth pathway depends on the presence of threonine in the ligand. The effective peptide vaccine will mimic the natural ligand, but won’t cause cell growth and division. Below is the sequence of the natural ligand:

LDMKTAG

1. In order to ensure your newly designed peptide vaccine does not cause cell growth upon binding, you must substitute the Threonine residue at position 5. What amino acid would you replace it with, bearing in mind that the peptide should still be similar enough to bind to the gp100 protein in the surface of melanocytes. Explain your choice.
2. Your vaccine will be administered as a topical cream, and you require your peptide to have an overall neutral charge in order to be functional. At what pH should you formulate your cream to maintain a neutral charge on the peptide? Why is this a good pH? 
3. State and explain the four levels of protein structure.