High force catch bond mechanism of bacterial adhesion in the human gut

Abstract

Bacterial colonization of the human intestine requires firm adhesion of bacteria to insoluble substrates under hydrodynamic flow. Here we report the molecular mechanism behind an ultrastable protein complex responsible for resisting shear forces and adhering bacteria to cellulose fibers in the human gut. Using single-molecule force spectroscopy (SMFS), singlemolecule FRET (smFRET), and molecular dynamics (MD) simulations, we resolve two binding modes and three unbinding reaction pathways of a mechanically ultrastable R. champanellensis (Rc) Dockerin:Cohesin (Doc:Coh) complex. The complex assembles in two discrete binding modes with significantly different mechanical properties, with one breaking at 500 pN and the other at~200 pN at loading rates from 1-100 nN s −1. A neighboring X-module domain allosterically regulates the binding interaction and inhibits one of the lowforce pathways at high loading rates, giving rise to a catch bonding mechanism that manifests under force ramp protocols. Multi-state Monte Carlo simulations show strong agreement with experimental results, validating the proposed kinetic scheme. These results explain mechanistically how gut microbes regulate cell adhesion strength at high shear stress through intricate molecular mechanisms including dual-binding modes, mechanical allostery and catch bonds.

AFM in cellular and molecular microbiology

“…This can be explained by the allosteric properties of FimH whose binding pocket for mannose exists as an inactive lowaffinity state at low stress but switches to a tight high-affinity conformation under tensile load (Le Trong et al, 2010;Rabbani et al, 2018;Sauer et al, 2016;Thomas et al, 2006). Another catch bond involving allosteric regulation has recently been suggested by Liu et al (2020). They unraveled how gut microbes modulate cellular adhesion through mechanically stable Dockerin:Cohesin interactions in bacterial cellulosome protein complexes: at high loading rates (high shear) a domain neighboring the Dockerin domain allosterically inhibits the low-force unbinding pathway of the complex, giving rise to a catch binding mechanism and shear-enhanced bacterial adhesion.…”

Single-Chain Mechanical Properties of Gelatin: A Single-Molecule Study

“…Polymers with specific structures undergo significant conformational changes, and such conformational changes have been found to be reversible [ 24 , 25 , 26 , 27 ]. In the biological field, combining molecular cell biology with SMFS, the complexity of cell or bacterial adhesion is explored to clarify the mechanism by which cell signaling processes enhance adhesion [ 28 , 29 , 30 , 31 ]. In the field of physical chemistry, the single-chain mechanical behavior of polymers in different environments can be obtained by SMFS to explore the interactions between single polymer chains and the surrounding environment [ 32 , 33 , 34 , 35 , 36 , 37 ].…”

Role of Cel5H protein surface amino acids in binding with clay minerals and measurements of its forces

“…On the same lines, our previous study also observed high amount of proteins on the edges of clay minerals and some absorbed in the cracks upon observing images taken from Atomic Force Microscopy (Math et al 2019 ). AFM, a powerful tool used for single-molecule interaction between protein-ligand (Sumbul and Rico 2019 ), clay minerals-protein (Math et al 2019 ), affinity under in-vitro conditions and protein-substrates like cellulose (Liu et al 2020 ). Also, rupture forces of cellulose binding module and fiber substrates of cellulose, were measured using AFM (Griffo et al 2019 ), and an adhesive force were successfully measured between pesticide degrading enzyme-soil particles (Islam et al 2017 ).…”

“…The prediction of structure of biomolecules like protein helps in studying protein-protein, protein-substrate and protein-fiber interactions (Moro et al 2016 ; Liu et al 2020 ; Moro et al 2020 ). The amino acid (aa) sequence of a protein, the so-called primary structure, can be easily determined from the sequence on the gene that codes for it.…”