In: Biology
How many fragments would be produced from trypsin digestion if all the positively charged residues in the heparin-binding region of hFGF-1 (FVGLKKNGSCKRGPRTHYGQK) were replaced with negatively charged residues?
Ans. FVGLKKNGSCKRGPRTHYGQK
Step 1: Basic amino acids (R, K and H) are positively charged. Replace theses residues with negatively charged residue, say aspartate, D. So, the new sequence is-
FVGLDDNGSCDDGPDTDYGQD
Step 2. Trypsin cleaves a peptide bond at the C-terminal of K and R residues except they’re not followed by a proline residues at C-terminal. Since all R and K residues are replaced by negatively charged residues, there is no more trypsin cleavage site. So, the peptide will not be fragmented/ cleaved upon trypsin treatment.