Question

Please be clear with how you determined the code sequence and isoelectric point

7. A single 14 amino acid peptide chain is to be assigned from the following experimental information below, your job is to provide the full triple letter code sequence (if possible), calculate its isoelectrie point and show your logie behind your answer. (12 marks) Experimental information: (i) Amino acid analysis: Cx2, Exl, Fxl, Wx1, Gx1, Hx1, Axl, Lx1, Dx2, Rx1, Qxl, and Nxl. (ii) Chymotrypsin Digestion of the intact peptide produced 3 peptide fragments that were then exposed to Edman degradation analysis, they provided the following sequence information: Fragment 1: LREG Fragment 2: CAHQF Fragment 3: DNCDW (ii) Trypsin Digestion of the intact peptide provided two peptide fragments. When those two fragments were subjected to FDNB, Cystine and Glutamate were the resides detected.

Answer 1

Sangers reagent determines the amino terminal aminoacid in the peptide sequence. Sanger's reaction gave cysteine and glutamate. Chymotrypsin digestion provides 3 different fragments. So, the sequence of peptide is,

NH2 - CAHQFLREGDNCDW - COOH

The peptide has 2 positive (histidine and arginine) amino acids. It also has 3 negative (2 aspartate and 1 glutamate) amino acids. So, the net charge on protein sequence is -1.