  The type 1 pilus is a bacterial filament consisting of a long coiled proteic
chain of subunits joined together by non-covalent bonding between complementing
$\beta$-strands. Its strength and structural stability are critical for its
anchoring function in uropathogenic Escherichia coli bacteria. The pulling and
unravelling of the FimG subunit of the pilus was recently studied by atomic
force microscopy (AFM) experiments and steered molecular dynamics (SMD)
simulations [A. Alonso-Caballero et al., Nature Commun. 9, 2758 (2018)]. In
this work we perform a quantitative comparison between experiment and
simulation, showing a good agreement in the underlying work values for the
unfolding. The simulation results are then used to estimate the free energy
difference for the detachment of FimG from the complementing strand of the
neighbouring subunit in the chain, FimF. Finally, we show that the large free
energy difference for the unravelling and detachment of the subunits which
leads to the high stability of the chain is entirely entropic in nature.
