Final answer:
A single amino acid mutation in hemoglobin can destabilize its T-state conformation, as seen in sickle cell anemia, leading to a higher oxygen affinity due to a shift to the R-state.
Step-by-step explanation:
A single amino acid mutation can have significant impacts on the structure and function of hemoglobin (Hb). For instance, in sickle cell anemia, the substitution of glutamic acid with valine in the beta chain of Hb leads to the aggregation of protein molecules and formation of long fibers. This alteration from a hydrophilic amino acid to a hydrophobic one at the sixth position destabilizes the T-state conformation of Hb. Consequently, this destabilization can cause red blood cells to assume a sickle shape, which is less efficient at traveling through blood vessels and delivering oxygen to tissues.
The oxygen affinity of mutant Hb, as seen in the Cowtown variant, is altered compared to wild-type Hb due to disruption of the T-state leading to impaired oxygen release from Hb in peripheral tissues. This shift to the R-state signifies a higher affinity for oxygen, which is beneficial in the lungs where oxygen is abundant but detrimental in tissues needing oxygen delivery. The myoglobin (Mb), with its higher oxygen affinity and lack of cooperative binding compared to Hb, continues to efficiently deliver oxygen to muscle tissues even at low partial pressures. However, the altered Hb variant would potentially release less oxygen, affecting overall tissue oxygenation.
Contrasting this to HbM or methemoglobin, where histidine is replaced, affecting the iron within the heme group, leading to oxidation and an inability to bind oxygen, the single amino acid mutation in the Cowtown variant of Hb and sickle cell anemia (HbS) still allows oxygen binding but affects the conformational changes required for efficient oxygen delivery.