Question

In the variant hemoglobin C, glutamate at position 6 of the β chain has been replaced with lysine. (a) Would you expect this mutant hemoglobin to polymerize as hemoglobin S does? (b) Red blood cells containing hemoglobin C have a shorter lifespan than red blood cells containing normal hemoglobin. How might this affect a person’s resistance to malaria?

Short answer

1. Hemoglobin C is not expected to polymerize as hemoglobin S does.
2. A person with red blood cells containing hemoglobin C would be less resistant to malaria.

Step-by-step solution

Hemoglobin S

In hemoglobin S, the mutant Val side chain of one hemoglobin S molecule binds to a hydrophobic pocket on the surface created by the β subunit of another molecule. This binding attraction mostly happens due to the non-polar interaction between the hydrophobic pocket and Val residue.

(a) Whether hemoglobin C polymerizes as hemoglobin S

In hemoglobin C, the glutamate at the 6^th position of the β chain was replaced with lysine. This mutation occurs at the same position where hemoglobin S is mutated.

However, owing to the polar positive nature of lysine residue, it is unlikely that the Lys residue would bind to the hydrophobic pocket of the β chain. Thus, this mutant hemoglobin C is not expected to polymerize as hemoglobin S does.

(b) A person’s resistance to malaria with hemoglobin C

The malaria-causing protozoan, Plasmodium falciparum, grows and replicates inside the blood cells, and eventually leads to the rupture of the cell. Thus, the red blood cell count decreases during the course of malaria.

During such a crisis of red blood cells, a patient having red blood cells containing hemoglobin C, which has a shorter life span, would affect negatively. That means the resistance to malaria would decrease.