Extreme mechanical stability in protein complexes

Recently, non-covalent protein complexes and folds with extreme mechanical stabilities have been discovered. Various extracellular adhesin proteins of gram-positive bacteria exhibit complex rupture forces ranging from 800 pN in the case of cellulolytic bacteria to over 2000 pN withstood by pathogens adhering to their hosts. Here, we review and assess the mechanics of such systems, and discuss progress, as well as open questions regarding their biological function, and underlying molecular mechanisms - in particular the role of increased interaction lifetimes under mechanical load. These unexpected extreme strengths open an unchartered range of protein mechanics that can now be routinely probed by atomic force microscopy-based single-molecule force spectroscopy.