Ultrastable cellulosome-adhesion complex tightens under load.

Constantin Schoeler,Markus A Jobst,Hermann E Gaub,Klaus Schulten,Ellis Durner,Daniel B Fried,Klara H Malinowska,Wolfgang Ott,Michael A Nash,Edward A Bayer,Rafael C Bernardi,Lukas F Milles

doi:10.1038/ncomms6635

Abstract

Challenging environments have guided nature in the development of ultrastable protein complexes. Specialized bacteria produce discrete multi-component protein networks called cellulosomes to effectively digest lignocellulosic biomass. While network assembly is enabled by protein interactions with commonplace affinities, we show that certain cellulosomal ligand–receptor interactions exhibit extreme resistance to applied force. Here, we characterize the ligand–receptor complex responsible for substrate anchoring in the Ruminococcus flavefaciens cellulosome using single-molecule force spectroscopy and steered molecular dynamics simulations. The complex withstands forces of 600–750 pN, making it one of the strongest bimolecular interactions reported, equivalent to half the mechanical strength of a covalent bond. Our findings demonstrate force activation and inter-domain stabilization of the complex, and suggest that certain network components serve as mechanical effectors for maintaining network integrity. This detailed understanding of cellulosomal network components may help in the development of biocatalysts for production of fuels and chemicals from renewable plant-derived biomass.

Highlights

Challenging environments have guided nature in the development of ultrastable protein complexes
Cellulosomes are protein networks designed by nature to degrade lignocellulosic biomass[1]
We chose an XModDoc:Coh complex responsible for maintaining bacterial adhesion to cellulose in the rumen

Summary

Introduction

Challenging environments have guided nature in the development of ultrastable protein complexes. We perform AFM single-molecule force spectroscopy experiments and steered molecular dynamics simulations to understand the mechanostability of the XModDoc:Coh cellulosomal ligand–receptor complex. We conclude that the high mechanostability we observe originates from molecular mechanisms, including stabilization of Doc by the adjacent XMod domain and catch bond behaviour that causes the complex to increase in contact area on application of force.

Results

Conclusion