Question

Choose a homolog of pepsin (for the purpose of this assignment, a homolog is one of the family of "homologous" proteins with common sequence elements indicative of a common evolutionary origin and similar structure) on the PDB.

a. What is the PDB ID of the protein you chose?

b. How many residues does it have?

c. What is its molecular mass?

d. What is the biological/physiological function of the protein you chose?

e. What particular kind of chemical reaction does it catalyze?

f. What other biological/physiological functions do acid proteases have?

Answer 1

a) PDB ID of Chymosin B (the chosen pepin protein homolog) is 4CMS.

b) It has a length of 323 amino acid residues.

c) Its molecular weight is 35.7 kDa (kilodaltons).

d) Its physiological function is to break down milk protein in young calves.

e) It cleaves the Phe¹⁰⁵-Met¹⁰⁶ bond in the milk protein k-casein, resulting in instability in milk micelles leading to clotting.

f) Proteolytic activity under acidic condition, milk clotting function in stomach.