Question

In relation to Lysozyme- i) What is the chemical nature of the lysozyme substrate? 2 Marks ii) Describe in detail the catalytic mechanism of Lysozyme

Answer 1

i) Chemical nature of lysozyme substrate:

The natural substrate of lysozyme is the peptidoglycan of bacterial cell wall. This peptodoglycan is a mesh-like polymer of sugars and amino acids. The sugar component is made up of alternating NAM and NAG residues crosslinked to each other via glycosidic beta 1-4 linkage. It is this glycoside bond that the lysozyme cleaves and lyses the cell wall.

ii) Catalytic mechanism:

Catalysis depends on the presence of Glu35 (hydrophobic environment) and Asp52 (polar environment) in the active site. Glu35 acts as a general acid and mediates the cleavage of the glycoside resulting in the formation of an oxonium ion intermediate. Glu35 attacks and protonates the acetal O1 of the D-NAM ring by breaking the C1-O1 bond. Now Asp52 aids in stabilizing this intermediate ion via electrolytic catalysis. This results in the formation of glycosyl - enzyme intermediate. Enzyme is regenerated via reprotonation of Glu35 by water.