RESUMEN
The flexibility of the ATP synthase's ß subunit promotes its role in the ATP synthase rotational mechanism, but its domains stability remains unknown. A reversible thermal unfolding of the isolated ß subunit (Tß) of the ATP synthase from Bacillus thermophilus PS3, tracked through circular dichroism and molecular dynamics, indicated that Tß shape transits from an ellipsoid to a molten globule through an ordered unfolding of its domains, preserving the ß-sheet residual structure at high temperature. We determined that part of the stability origin of Tß is due to a transversal hydrophobic array that crosses the ß-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.