Hbs tetramerHemoglobin crystals

Sickle-Cell Hemoglobin (HbS)

    Hemoglobin is a tetrameric protein with two alpha and two beta subunit chains. The standard form is HbA. In the HbS form, replacement of the amino acid residue Glu by Val in the two beta subunits (dark grey) increases the negative electrical charge where they contact the alpha subunits [top, left]. Under conditions of reduced oxygen tension in the blood, the modified tetramer undergoes a conformational shift that forms stable crystals [top, right]. Crystal formation deforms the standard toroidal form of red blood cells to sickle-shaped cells [below].

All text material © 2014 by Steven M. Carr