Ordered-domain unfolding of thermophilic isolated β subunit ATP synthase

The flexibility of the ATP synthase's beta subunit promotes its role in the ATP synthase rotational mechanism, but its domains stability remains unknown. A reversible thermal unfolding of the isolated beta subunit (T beta) of the ATP synthase from Bacillus thermophilus PS3, tracked through circular dichroism and molecular dynamics, indicated that T beta shape transits from an ellipsoid to a molten globule through an ordered unfolding of its domains, preserving the beta-sheet residual structure at high temperature. We determined that part of the stability origin of T beta is due to a transversal hydrophobic array that crosses the beta-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.