title: On the remarkable mechanostability of scaffoldins and the mechanical clamp motif.
abstract: Protein mechanostability is a fundamental biological property that can only be measured by single-molecule manipulation techniques. Such studies have unveiled a variety of highly mechanostable modules (mainly of the Ig-like, beta-sandwich type) in modular proteins subjected to mechanical stress from the cytoskeleton and the metazoan cell-cell interface. Their mechanostability is often attributed to a "mechanical clamp" of secondary structure (a patch of backbone hydrogen bonds) fastening their ends. Here we investigate the nanomechanics of scaffoldins, an important family of scaffolding proteins that assembles a variety of cellulases into the so-called cellulosome, a microbial extracellular nanomachine for cellulose adhesion and degradation. These proteins anchor the microbial cell to cellulose substrates, which makes their connecting region likely to be subjected to mechanical stress. By using single-molecule force spectroscopy based on atomic force microscopy, polyprotein engineering, and computer simulations, here we show that the cohesin I modules from the connecting region of cellulosome scaffoldins are the most robust mechanical proteins studied experimentally or predicted from the entire Protein Data Bank. The mechanostability of the cohesin modules studied correlates well with their mechanical kinetic stability but not with their thermal stability, and it is well predicted by computer simulations, even coarse-grained. This extraordinary mechanical stability is attributed to 2 mechanical clamps in tandem. Our findings provide the current upper limit of protein mechanostability and establish shear mechanical clamps as a general structural/functional motif widespread in proteins putatively subjected to mechanical stress. These data have important implications for the scaffoldin physiology and for protein design in biotechnology and nanotechnology.
authors: Instituto Cajal, Consejo Superior de Investigaciones Científicas and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, Avenida Doctor Arce 37, E-28002 Madrid, Spain.
authors: Alejandro
authors: A
authors: Valbuena
authors: Javier
authors: J
authors: Oroz
authors: Rubén
authors: R
authors: Hervás
authors: Andrés Manuel
authors: AM
authors: Vera
authors: David
authors: D
authors: Rodríguez
authors: Margarita
authors: M
authors: Menéndez
authors: Joanna I
authors: JI
authors: Sulkowska
authors: Marek
authors: M
authors: Cieplak
authors: Mariano
authors: M
authors: Carrión-Vázquez
mesh_terms: D020816:Amino Acid Motifs; D001709:Biotechnology / Q000379:methods; D002482:Cellulose / Q000737:chemistry; D048013:Acetivibrio thermocellus / Q000378:metabolism*; D003198:Computer Simulation; D030562:Databases, Protein; D007700:Kinetics; D018625:Microscopy, Atomic Force / Q000379:methods; D036103:Nanotechnology / Q000379:methods; D011487:Protein Conformation; D015202:Protein Engineering / Q000379:methods; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D013314:Stress, Mechanical
chemical_list: D011506:Proteins; D002482:Cellulose