https://nanomechanics.mit.edu/sites/default/files/documents/2007_Acta_Bio_Cancer_S.Suresh.pdf

Biomechanics and biophysics of cancer cells.

Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Dextran filaments linked to a gold surface were probed with the atomic force microscope tip by vertical stretching. At low forces the deformation of dextran was found to be dominated by entropic forces and can be described by the Langevin function with a 6 angstrom Kuhn length. At elevated forces the strand elongation was governed by a twist of bond angles. At higher forces the dextran filaments underwent a distinct conformational change. The polymer stiffened and the segment elasticity was dominated by the bending of bond angles. The conformational change was found to be reversible and was corroborated by molecular dynamics calculations.

https://science.sciencemag.org/content/sci/275/5304/1295.full.pdf

Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy

Is the mechanical unraveling of protein domains by atomic force microscopy (AFM) just a technological feat or a true measurement of their unfolding? By engineering a protein made of tandem repeats of identical Ig modules, we were able to get explicit AFM data on the unfolding rate of a single protein domain that can be accurately extrapolated to zero force. We compare this with chemical unfolding rates for untethered modules extrapolated to 0 M denaturant. The unfolding rates obtained by the two methods are the same. Furthermore, the transition state for unfolding appears at the same position on the folding pathway when assessed by either method. These results indicate that mechanical unfolding of a single protein by AFM does indeed reflect the same event that is observed in traditional unfolding experiments. The way is now open for the extensive use of AFM to measure folding reactions at the single-molecule level. Single-molecule AFM recordings have the added advantage that they define the reaction coordinate and expose rare unfolding events that cannot be observed in the absence of chemical denaturants.

https://www.pnas.org/content/pnas/96/7/3694.full.pdf

Mechanical and Chemical Unfolding of a Single Protein: A Comparison

https://www.physics.uci.edu/~tritz/BP/ISRA2001.pdf

Steered molecular dynamics and mechanical functions of proteins

Extracellular matrix proteins are thought to provide a rigid mechanical anchor that supports and guides migrating and rolling cells. Here we examine the mechanical properties of the extracellular matrix protein tenascin by using atomic-force-microscopy techniques. Our results indicate that tenascin is an elastic protein. Single molecules of tenascin could be stretched to several times their resting length. Force-extension curves showed a saw-tooth pattern, with peaks of force at 137pN. These peaks were approximately 25 nm apart. Similar results have been obtained by study of titin. We also found similar results by studying recombinant tenascin fragments encompassing the 15 fibronectin type III domains of tenascin. This indicates that the extensibility of tenascin may be due to the stretch-induced unfolding of its fibronectin type III domains. Refolding of tenascin after stretching, observed when the force was reduced to near zero, showed a double-exponential recovery with time constants of 42 domains refolded per second and 0.5 domains per second. The former speed of refolding is more than twice as fast as any previously reported speed of refolding of a fibronectin type III domain. We suggest that the extensibility of the modular fibronectin type III region may be important in allowing tenascin-ligand bonds to persist over long extensions. These properties of fibronectin type III modules may be of widespread use in extracellular proteins containing such domain.

The molecular elasticity of the extracellular matrix protein tenascin

Sensing specific molecular interactions with the atomic force microscope

https://www.cell.com/biophysj/pdf/S0006-3495(99)77322-4.pdf

Adhesion energy of receptor-mediated interaction measured by elastic deformation

The atomic force microscope (AFM) is capable of measuring the interaction between tip and sample with high sensitivity and unparalleled spatial resolution. The chemical functionalization of the AFM tips has expanded the versatility of the AFM to experiments where specific molecular interactions are measured. We present here measurements of the interaction between complementary strands of DNA. A necessary prerequisite for the quantitative analysis of the interaction force is knowledge of the spring constant of the cantilevers. We report a method that allows for the in situ measurement of the absolute value of the spring constant of cantilevers based on spectral analysis of the thermal excitations of the cantilever.

Horst Lehmann

Papers

Sensing specific molecular interactions with the atomic force microscope

Adhesion energy of receptor-mediated interaction measured by elastic deformation

Probing the forces between complementary strands of DNA with the atomic force microscope