Question

In the first step of the peptidoglycan hydrolysis reaction, the N-acetylglucosamine product (NAG, with attached sugar chain) is released. To emphasize the newly formed hydroxyl group on the product, the product will be referred to as NAG-OH. As the glycosidic C–O bond breaks and NAG-OH is being formed, the oxygen atom begins to develop a negative charge making it unstable. However, several features of the lysozyme active site promote the stabilization of the NAG-OH leaving group as it is being formed. Select the best explanations of how the lysozyme active site contributes to the formation and stabilization of the NAG-OH leaving group. Note: If your book or professor has not covered these specifics, then choose answers that are not self-contradictory.

1. Glu35 has an abnormally high pKa of ~6 (normal pKa= 4) due to the surronding nonpolar environment. This pKa shift allows Glu35 to donate the proton that results in the stable NAG-OH leaving group. Note: Lysozyme has optimum activity around pH 5.

2.A water molecule in the active site acts as a specific base and donates an OH– to form the NAG-OH leaving group.

3.Asp52 acts a general base to form the stable NAG-OH leaving group.

4. The developing negative charge on the glycosidic oxygen atom of NAG is neutralized when it is protonated by Glu35.

Answer 1