AHSP (α-haemoglobin-stabilizing protein) stabilizes apo-α-haemoglobin in a partially folded state

To produce functional Hb (haemoglobin), nascent α-globin (αo) and β-globin (βo) chains must each bind a single haem molecule (to form αh and βh) and interact together to form heterodimers. The precise sequence of binding events is unknown, and it has been suggested that additional factors might enhance the efficiency of Hb folding. AHSP (α-haemoglobin-stabilizing protein) has been shown previously to bind αh and regulate redox activity of the haem iron. In the present study, we used a combination of classical and dynamic light scattering and NMR spectroscopy to demonstrate that AHSP forms a heterodimeric complex with αo that inhibits αo aggregation and promotes αo folding in the absence of haem. These findings indicate that AHSP may function as an αo-specific chaperone, and suggest an important role for αo in guiding Hb assembly by stabilizing βo and inhibiting off-pathway self-association of βh.