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Single Molecule Force Spectroscopy Reveals the Mechanical Design Governing the Efficient Translocation of the Bacterial Toxin Protein RTX
journal contribution
posted on 2019-12-15, 15:03 authored by Han Wang, Xiaoqing Gao, Hongbin LiThe efficient translocation of the bacterial toxin adenylate
cyclase
toxin (CyaA) from the bacterial cytosol to the extracellular environment
by the type 1 secretion system (T1SS) is essential for the toxin to
function. To understand the molecular features that are responsible
for the efficient translocation of CyaA, here we used optical tweezers
to investigate the mechanical properties and conformational dynamics
of the RTX domain of CyaA at the single molecule level. Our results
revealed that apo-RTX behaves like an ideal random coil. This property
allows the T1SS to translocate RTX without overcoming the enthalpic
resistance. In contrast, the folded holo-RTX is mechancially stable,
and its folding occurs in a vectorial, cotranslocational fashion starting
from its C-terminus. Moreover, our results showed that the folding
of holo-RTX generates a stretching force, which can further facilitate
the translocation of RTX. Our results highlight the important role
played by the Ca2+-triggered folding of RTX in the translocation
of RTX and provide mechanistic insights into the mechanical design
that governs the efficient translocation of RTX.