title: Exploring the molecular forces within and between CbsA S-layer proteins using single molecule force spectroscopy.
abstract: We used single molecule atomic force microscopy (AFM) to gain insight into the molecular forces driving the folding and assembly of the S-layer protein CbsA. Force curves recorded between tips and supports modified with CbsA proteins showed sawtooth patterns with multiple force peaks of 58+/-26pN that we attribute to the unfolding of alpha-helices, in agreement with earlier secondary structure predictions. The average unfolding force increased with the pulling speed but was independent on the interaction time. Force curves obtained for CbsA peptides truncated in their C-terminal region showed similar periodic features, except that fewer force peaks were seen. Furthermore, the average unfolding force was 83+/-45pN, suggesting the domains were more stable. By contrast, cationic peptides truncated in their N-terminal region showed single force peaks of 366+/-149pN, presumably reflecting intermolecular electrostatic bridges rather than unfolding events. Interestingly, these large intermolecular forces increased not only with pulling speed but also with interaction time. We expect that the intra- and intermolecular forces measured here may play a significant role in controlling the stability and assembly of the CbsA protein.
authors.affiliation: Unité de chimie des interfaces, Université catholique de Louvain, Croix du Sud 2/18, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Claire
authors.initials: C
authors.lastname: Verbelen
authors.forename: Jenni
authors.initials: J
authors.lastname: Antikainen
authors.forename: Timo K
authors.initials: TK
authors.lastname: Korhonen
authors.forename: Yves F
authors.initials: YF
authors.lastname: Dufrêne
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D008562:Membrane Glycoproteins / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods*; D017510:Protein Folding
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins