Unbinding events

Detecting unbinding events

In order to detect unbinding events, go to the compute tab and click “Detect Event”

../_images/compute_event.png

If the “All file” option is on, it will compute the events on all the files of the experiments. We suggest you to make a first detection on only one file, and fine tune the detector. Once you are satisfied with the detector sensitivity, you can then apply the same settings on all files.

Tuning the event detector

After performing a first detection run, display the result as a map showing the position and the force of the detected events by clicking on “event array” or “event force array” buttons in the display tab.

../_images/display_event_map.png

The event map shows the number of detected unbinding events for each pixels in the scan. The event force map shows the strongest event unbinding force measured in each pixel, meaning that, if two or more events are detected in a single pixel (i.e. force-distance curve), it will display as a gray scale the value of the strongest one.

With these two maps, you see the events that have been detected, and which were not. You can adjust the detection sensitivity with the “Adjust sensitivity” button of the “Parameters” tab.

../_images/Parameters_event_sensitivity.png

By clicking on “Adjust sensitivity”, an horizontal scrollbar appears on the curve window. The retraction curve and the unbinding event detection is enabled, allowing to directly see the result of the sensitivity modifications. By scrolling to the right, the detector is made more sensitive. Once the sensitivity of the detector has been adjusted apply the changes to your data by clicking “Detect Events” on the “Compute” tab.

../_images/curve_event_adjust.png

Choosing the fit model

OpenFovea permits to fit the detected event with the “worm like chain” or the “free joint chain” model. These models estimates the length and persistent length of your molecule. For information, the persistent length of a molecule is a mechanical properties that describes a string, like a protein. This value is the distance at which information of the orientation are lost. One part of the string is influenced by the orientation of another part only if they are separated by a distance smaller than the persistance length.

The different models are accessible by clicking on the “Event fit model” list.

../_images/Parameters_event_fit_model.png

Displaying the results

After detecting unbinding events, you can plot the results.

../_images/event_result_histogram.png

Histograms shows the unbinding events distribution as a function of force, loading rate and distance.

../_images/event_display_histogram.png

All the histograms are parametrable : if you want to display the force histogram, click on the “Histogram” button on the “force” column. To change the minimum or maximum force scale, use the spin button in the corresponding column. The “col size” parameter permits to modify the column width.

Filtering the results

The results can be filtered according to the distance where events occurred or the event length computed from the chosen model.

In the parameter tab, you will find tools to modify the distance threshold (blue box in the top). Automatically, the information in the bottom is updated according to this value (blue box in the bottom).

../_images/Parameters_distance_threshold.png

Notice that, if you select “Apply on all” and your files have a different threshold, the information displayed in the bottom of the window will be “~~” to warn you that all the files does not have the same threshold value. By modifying the distance threshold while enabling “apply on all”, the change will affect all the files.

In the same tab, you will find the tools to filter the events according to the values returned by the chosen fit (WLC or FJC model). The event length threshold is chosen using the input (blue box in the top). This parameter is used to reject unbinding events that do not fit with expected values from the displayed results.

Automatically, the information in the bottom is updated according to this value (blue box in the bottom).

../_images/Parameters_ev_length_threshold.png

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