Cooperativity in Thermal and Force-Induced Protein Unfolding: Integration of Crack Propagation and Network Elasticity Models

Amit Srivastava and Rony Granek

We investigate force-induced and temperature-induced unfolding of proteins using the combination of a Gaussian network model and a crack propagation model based on “bond”-breaking independent events. We assume the existence of threshold values for the mean strain and strain fluctuations that dictate bond rupture. Surprisingly, we find that this stepwise process usually leads to a few cooperative, first-order-like, transitions in which several bonds break simultaneously, reminiscent of the “avalanches” seen in disordered networks.

DOI

Journal: Physical Review Letters

Multistep protein unfolding during nanopore translocation

David Rodriguez-Larrea, and Hagan Bayley

Cells are divided into compartments and separated from the environment by lipid bilayer membranes. Essential molecules are transported back and forth across the membranes. We have investigated how folded proteins use narrow transmembrane pores to move between compartments. During this process, the proteins must unfold. To examine co-translocational unfolding of individual molecules, we tagged protein substrates with oligonucleotides to enable potential-driven unidirectional movement through a model protein nanopore, a process that differs fundamentally from extension during force spectroscopy measurements. Our findings support a four-step translocation mechanism for model thioredoxin substrates. First, the DNA tag is captured by the pore. Second, the oligonucleotide is pulled through the pore, causing local unfolding of the C terminus of the thioredoxin adjacent to the pore entrance. Third, the remainder of the protein unfolds spontaneously. Finally, the unfolded polypeptide diffuses through the pore into the recipient compartment. The unfolding pathway elucidated here differs from those revealed by denaturation experiments in solution, for which two-state mechanisms have been proposed.

DOI

Journal: Nature Nanotechnology

Mechanical Activation of a Multimeric Adhesive Protein Through Domain Conformational Change

Sithara S. Wijeratne, Eric Botello, Hui-Chun Yeh, Zhou Zhou, Angela L. Bergeron, Eric W. Frey, Jay M. Patel, Leticia Nolasco, Nancy A. Turner, Joel L. Moake, Jing-fei Dong, and Ching-Hwa Kiang

The mechanical force-induced activation of the adhesive protein von Willebrand factor (VWF), which experiences high hydrodynamic forces, is essential in initiating platelet adhesion. The importance of the mechanical force-induced functional change is manifested in the multimeric VWF’s crucial role in blood coagulation, 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 found that shear-activated PVWF multimers are more resistant to mechanical unfolding than nonsheared PVWF multimers, as indicated in the higher peak unfolding force. These results provide insight into the mechanism of shear-induced activation of PVWF multimers.

DOI

Journal: Physical Review Letters