title: Temperature softening of a protein in single-molecule experiments.
abstract: Mechanical flexibility is crucial for the function of proteins. However, such material properties are not easily accessible experimentally. We used single-molecule force spectroscopy to study the stiffness of a single domain of Dictyostelium discoideum filamin (ddFLN4) in a temperature range from 5 degrees C to 37 degrees C. Analyzing the distributions of unfolding forces allowed us to extract transition barrier heights and positions of the underlying energy landscape. We found a marked narrowing of unfolding force distributions with increasing temperature. This narrowing reflects an increase in transition state position from 2.7 A to 7.8 A and thus a reduction of the molecular spring constant of the protein by a factor of 7. We suggest this temperature softening reflects a shift in the nature of the interactions responsible for mechanical stability from hydrogen bonds to hydrophobic interactions. This result has important consequences for all interpretations of protein mechanical studies if experimental results obtained at room temperature are to be transferred to physiological temperatures.
authors.affiliation: Physik Department E22, Technische Universität München, James-Franck-Strasse, D-85748 Garching b. München, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schlierf
authors.forename: Matthias
authors.initials: M
authors.lastname: Rief
mesh_terms: D000818:Animals; D003285:Contractile Proteins / Q000737:chemistry* / Q000378:metabolism; D004023:Dictyostelium / Q000737:chemistry*; D064448:Filamins; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D013696:Temperature
chemical_list: D003285:Contractile Proteins; D064448:Filamins; D008840:Microfilament Proteins