Single-Molecule Dynamics
of Lysozyme Processing Distinguishes
Linear and Cross-Linked Peptidoglycan Substrates
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Abstract
The dynamic processivity of individual T4 lysozyme molecules
was
monitored in the presence of either linear or cross-linked peptidoglycan
substrates. Single-molecule monitoring was accomplished using a novel
electronic technique in which lysozyme molecules were tethered to
single-walled carbon nanotube field-effect transistors through pyrene
linker molecules. The substrate-driven hinge-bending motions of lysozyme
induced dynamic electronic signals in the underlying transistor, allowing
long-term monitoring of the same molecule without the limitations
of optical quenching or bleaching. For both substrates, lysozyme exhibited
processive low turnover rates of 20–50 s<sup>–1</sup> and rapid (200–400 s<sup>–1</sup>) nonproductive motions.
The latter nonproductive binding events occupied 43% of the enzyme’s
time in the presence of the cross-linked peptidoglycan but only 7%
with the linear substrate. Furthermore, lysozyme catalyzed the hydrolysis
of glycosidic bonds to the end of the linear substrate but appeared
to sidestep the peptide cross-links to zigzag through
the wild-type substrate