Ordered‐domain unfolding of thermophilic isolated β subunit ATP synthase

The flexibility of the ATP synthase's β subunit promotes its role in the ATP synthase rotational mechanism, but its domains stability remains unknown. A reversible thermal unfolding of the isolated β subunit (Tβ) of the ATP synthase from Bacillus thermophilus PS3, tracked through circular dichroism and molecular dynamics, indicated that Tβ shape transits from an ellipsoid to a molten globule through an ordered unfolding of its domains, preserving the β‐sheet residual structure at high temperature. We determined that part of the stability origin of Tβ is due to a transversal hydrophobic array that crosses the β‐barrel formed at the N‐terminal domain and the Rossman fold of the nucleotide‐binding domain (NBD), while the helix bundle of the C‐terminal domain is the less stable due to the lack of hydrophobic residues, and thus the more flexible to trigger the rotational mechanism of the ATP synthase.