AHSP Protein, Human, Recombinant

AHSP, also known as ERAF, is a conserved mammalian erythroid protein which belongs to the AHSP family. It is expressed in blood and bone marrow. AHSP facilitates the production of Hemoglobin A by stabilizing free α-globin. It rapidly binds to ferrous α with association (k' (AHSP) ) and dissociation (k (AHSP) ) rate constants of ≈1 μm (-1) s (-1) and .2 s (-1), respectively, at pH 7.4 at 22 °C. A small slow phase was observed when AHSP binds to excess ferrous αCO. This slow phase appears to be due to cis to trans prolyl isomerization of the Asp (29) -Pro (3) peptide bond in wild-type AHSP because it was absent when αCO was mixed with P3A and P3W AHSP, which are fixed in the trans conformation. This slow phase was also absent when met (Fe (3+) ) -α reacted with wild-type AHSP, suggesting that met-α is capable of rapidly binding to either Pro (3) conformer. Both wild-type and Pro (3) -substituted AHSPs drive the formation of a met-α hemichrome conformation following binding to either met- or oxy (Fe (2+) ) -α. The dissociation rate of the met-α·AHSP complex (k (AHSP) ≈ .2 s (-1) ) is ~1-fold slower than that for ferrous α·AHSP complexes, resulting in a much higher affinity of AHSP for met-α. Thus, in vivo, AHSP acts as a molecular chaperone by rapidly binding and stabilizing met-α hemichrome folding intermediates. The low rate of met-α dissociation also allows AHSP to have a quality control function by kinetically trapping ferric α and preventing its incorporation into less stable mixed valence Hemoglobin A tetramers. Reduction of AHSP-bound met-α allows more rapid release to β subunits to form stable fully, reduced hemoglobin dimers and tetramers.