Single Molecule Force Signatures in Biological Physics
Wijeratne, Sithara Suransi
Doctor of Philosophy
Single molecule manipulation has opened up new research frontiers in understanding how biology and medicine function at the microscopic level. Quantitative information on the structure, conformation and dynamics of biological molecules can be revealed by the single molecule force measurements. Recently single molecule manipulation via the atomic force microscope (AFM) has been used to characterize the mechanical force-induced activation of the adhesive protein von Willebrand factor (VWF), which is essential in initiating platelet adhesion. The mechanical force-induced functional change of VWF plays a crucial role in hemostasis, when high fluid shear stress activates plasma VWF (PVWF) multimers to bind platelets. Here, we showed that a pathological level of high shear stress exposure of PVWF multimers results in domain conformational changes, and the subsequent shifts in the unfolding force allow us to use force as a marker to track the dynamic states of the multimeric VWF. We also investigated the effect of high fluid shear stress on soluble dimeric VWF (DVWF). DVWF is the smallest unit that polymerizes to construct large VWF multimers. Our data indicate that, unlike PVWF multimers, DVWF is not altered by high shear stress. We conclude that DVWF is not capable of self-association under shear into a conformation analogous to that attained by sheared large VWF multimers. Single molecule force signatures were also used to characterize the mechanical properties of proteins related to the complement system and the extracellular matrix. Beyond the investigation of proteins, we applied this technique to understand the mechanical behavior of graphene nanoribbons, a potential biomaterial, which revealed a biopolymer behavior. Finally, the AFM technique can be extended from probing single molecules to capturing characteristics of the whole cell. These single cell experiments revealed the forces related to pulling tethers from the cell membrane.
Atomic Force Microscopy; Single Molecule Manipulation, Proteins, Force, Biological Physics, von Willebrand Factor