Browsing by Author "Guo, Senli"

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Open Access
Kinetic Parameters from Detection Probability in Single Molecule Force Spectroscopy
(2010) Ray, Chad; Guo, Senli; Brown, Jason; Li, Nan; Akhremitchev, Boris B
The detection probability of rupture events in A FM force spectroscopy measurements presents a viable alternative to standard methods for extracting kinetic parameters of dissociation. The detection probability has a maximum as a function of the probe velocity where (1) the probability to form a molecular bond is independent of the probe velocity and (2) the detection of rupture events is limited by noise and performed with a constant density of data points per distance of the probe displacement. This newly developed model indicates that the optimal detection velocity is independent of dissociation rate and depends on the distance to the barrier kinetic parameter. Therefore, the kinetic parameters of bond dissociation can be extracted from the dependence of detection probability on probe velocity and the detection threshold. This approach is sensitive to low rupture forces and therefore is complementary to the common most probable force data analysis approach. The developed approach is tested using rupture forces measured with specific bonds between biotin and streptavidin and with nonspecific bonds between linear alkalies in water. Results for the analysis of specific bonds rupture are consistent with the previous measurements, suggesting that rupture forces spanning a wide range of values originate from the same binding potential. Kinetic parameters obtained for linear alkalies are significantly different from previous measurements suggesting possible heterogeneity of the bound state.
Open Access
Mechanical Distortion of Protein Receptor Decreases the Lifetime of a Receptor-Ligand Bond
(2010) Guo, Senli; Li, Nan; Lad, Nimit; Ray, Chad; Akhremitchev, Boris B
Substantial experimental evidence indicates that the mechanical force applied to pull apart non-covalent molecular bonds (such as receptor ligand pairs) can significantly decrease the bond lifetime. This evidence is often generated in single-molecule experiments that are designed to specifically test effects of pulling forces. However, the effect of compressive forces on the lifetime of receptor ligand bonds remains largely unexplored. Here we extend the common usage of the atomic force microscopy technique to study whether compressive forces applied to bound streptavidin-biotin species can significantly accelerate the rate of dissociation. Presented experimental data indicate that compressive forces can substantially decrease the lifetime of the molecular bond. Surprisingly, the efficiency of accelerating dissociation by compressive forces sometimes exceeds the enhancement of the dissociation rate measured in pulling experiments, indicating that compressive forces applied to the bound species might be efficiently used to control the lifetime of adhesion bonds.