title: Sequential unfolding of beta helical protein by single-molecule atomic force microscopy.
abstract: The parallel βhelix is a common fold among extracellular proteins, however its mechanical properties remain unexplored. In Gram-negative bacteria, extracellular proteins of diverse functions of the large 'TpsA' family all fold into long βhelices. Here, single-molecule atomic force microscopy and steered molecular dynamics simulations were combined to investigate the mechanical properties of a prototypic TpsA protein, FHA, the major adhesin of Bordetella pertussis. Strong extension forces were required to fully unfold this highly repetitive protein, and unfolding occurred along a stepwise, hierarchical process. Our analyses showed that the extremities of the βhelix unfold early, while central regions of the helix are more resistant to mechanical unfolding. In particular, a mechanically resistant subdomain conserved among TpsA proteins and critical for secretion was identified. This nucleus harbors structural elements packed against the βhelix that might contribute to stabilizing the N-terminal region of FHA. Hierarchical unfolding of the βhelix in response to a mechanical stress may maintain β-helical portions that can serve as templates for regaining the native structure after stress. The mechanical properties uncovered here might apply to many proteins with β-helical or related folds, both in prokaryotes and in eukaryotes, and play key roles in their structural integrity and functions.
authors.affiliation: Université catholique de Louvain, Institute of Condensed Matter and Nanosciences, Louvain-la-Neuve, Belgium. david.alsteens@uclouvain.be
authors.forename: David
authors.initials: D
authors.lastname: Alsteens
authors.forename: Nicolas
authors.initials: N
authors.lastname: Martinez
authors.forename: Marc
authors.initials: M
authors.lastname: Jamin
authors.forename: Françoise
authors.initials: F
authors.lastname: Jacob-Dubuisson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D005964:Glucosyltransferases / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D058767:Protein Unfolding; D011506:Proteins / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D011506:Proteins; D005964:Glucosyltransferases; C023180:trehalose-6-phosphate synthase