Unusually high mechanical stability of bacterial adhesin extender domains having calcium clamps

PLoS One. 2017 Apr 4;12(4):e0174682. doi: 10.1371/journal.pone.0174682. eCollection 2017.


To gain insight into the relationship between protein structure and mechanical stability, single molecule force spectroscopy experiments on proteins with diverse structure and topology are needed. Here, we measured the mechanical stability of extender domains of two bacterial adhesins MpAFP and MhLap, in an atomic force microscope. We find that both proteins are remarkably stable to pulling forces between their N- and C- terminal ends. At a pulling speed of 1 μm/s, the MpAFP extender domain fails at an unfolding force Fu = 348 ± 37 pN and MhLap at Fu = 306 ± 51 pN in buffer with 10 mM Ca2+. These forces place both extender domains well above the mechanical stability of many other β-sandwich domains in mechanostable proteins. We propose that the increased stability of MpAFP and MhLap is due to a combination of both hydrogen bonding between parallel terminal strands and intra-molecular coordination of calcium ions.

MeSH terms

  • Adhesins, Bacterial / chemistry*
  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / metabolism
  • Amino Acid Sequence
  • Binding Sites
  • Biomechanical Phenomena
  • Calcium / metabolism
  • Hydrogen Bonding
  • Marinobacter / chemistry
  • Marinobacter / genetics
  • Marinobacter / metabolism
  • Marinomonas / chemistry
  • Marinomonas / genetics
  • Marinomonas / metabolism
  • Microscopy, Atomic Force
  • Models, Molecular
  • Protein Domains
  • Protein Engineering
  • Protein Stability
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid


  • Adhesins, Bacterial
  • Recombinant Proteins
  • Calcium

Grant support

This work was supported by CIHR (operating grant 106612); NSERC (discovery grant RGPIN-2016-04810); European Union (ERC-2014-StG Contract No. 635928); and Dutch Ministry of Education, Culture and Science (Gravity Program 024.001.035). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.