What is the structural basis of sickle cell polymerization under low oxygen tension?
Answer and explanation
Correct answer: D. Hydrophobic contact between mutant Val6 and a hydrophobic pocket on an adjacent beta-chain
In deoxygenated HbS, a conformational shift exposes a hydrophobic pocket on the surface of the beta-globin subunit (formed by Phe85 and Leu88). The mutant hydrophobic valine residue at position 6 (Glu6Val) of an adjacent beta-chain fits into this pocket, causing HbS tetramers to polymerize into long, insoluble fibrous filaments that distort erythrocytes into rigid sickle shapes.
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