title: Mechanically unfolding the small, topologically simple protein L.
abstract: beta-sheet proteins are generally more able to resist mechanical deformation than alpha-helical proteins. Experiments measuring the mechanical resistance of beta-sheet proteins extended by their termini led to the hypothesis that parallel, directly hydrogen-bonded terminal beta-strands provide the greatest mechanical strength. Here we test this hypothesis by measuring the mechanical properties of protein L, a domain with a topology predicted to be mechanically strong, but with no known mechanical function. A pentamer of this small, topologically simple protein is resistant to mechanical deformation over a wide range of extension rates. Molecular dynamics simulations show the energy landscape for protein L is highly restricted for mechanical unfolding and that this protein unfolds by the shearing apart of two structural units in a mechanism similar to that proposed for ubiquitin, which belongs to the same structural class as protein L, but unfolds at a significantly higher force. These data suggest that the mechanism of mechanical unfolding is conserved in proteins within the same fold family and demonstrate that although the topology and presence of a hydrogen-bonded clamp are of central importance in determining mechanical strength, hydrophobic interactions also play an important role in modulating the mechanical resistance of these similar proteins.
authors.affiliation: School of Biochemistry and Microbiology, Institute of Molecular Biophysics, Centre for Chemical Dynamics, University of Leeds, Leeds, United Kingdom. brock@bmbaxp.leeds.ac.uk
authors.forename: David J
authors.initials: DJ
authors.lastname: Brockwell
authors.forename: Godfrey S
authors.initials: GS
authors.lastname: Beddard
authors.forename: Emanuele
authors.initials: E
authors.lastname: Paci
authors.forename: Dan K
authors.initials: DK
authors.lastname: West
authors.forename: Peter D
authors.initials: PD
authors.lastname: Olmsted
authors.forename: D Alastair
authors.initials: DA
authors.lastname: Smith
authors.forename: Sheena E
authors.initials: SE
authors.lastname: Radford
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001703:Biophysics / Q000379:methods*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D018625:Microscopy, Atomic Force / Q000379:methods*; D008958:Models, Molecular; D015233:Models, Statistical; D009010:Monte Carlo Method; D010462:Peptostreptococcus / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D025801:Ubiquitin / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C116593:L-protein, Peptococcus magnus; D011506:Proteins; D025801:Ubiquitin