Constantin Schoeler, Klara H. Malinowska, Rafael C. Bernardi, Lukas F. Milles,
Markus A. Jobst, Ellis Durner, Wolfgang Ott, Daniel B. Fried, Edward A.
Bayer, Klaus Schulten, Hermann E. Gaub, and Michael A. Nash.
Ultrastable cellulosome-adhesion complex tightens under load.
Nature Communications, 5:5635, 2014.
(PMC: PMC4266597)
SCHO2014
In contrast to the free enzymes secreted by a majority of cellulolytic microorganisms,
certain bacteria and fungi produce large multi-enzyme networks called cellulosomes to
convert plant cell walls into fermentable sugars. While network assembly is enabled by
protein interactions with commonplace affinities, we show here that certain cellulosomal
receptor–ligand interactions exhibit extreme resistance to applied force. Through single
molecule force spectroscopy (SMFS) and steered molecular dynamics (SMD) simulations, we
characterized the ligand–receptor complex responsible for substrate anchoring in the
Ruminococcus flavefaciens cellulosome. We found the complex withstands forces of 600-
750 pN at loading rates of 10-100 nN/s, representing the strongest bimolecular
interaction reported thus far, equivalent to half the mechanical strength of a covalent
bond. The binding mechanisms discovered including force-activation and inter-domain
stabilization suggest mechanical stability as an additional design parameter in the
development of biocatalysts for the production of fuels and chemicals from cellulosic
biomass.
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