Quantifying a light-induced energetic change in bacteriorhodopsin by force spectroscopy

Ligand-induced conformational changes are critical to the function of many membrane proteins and arise from numerous intramolecular interactions. In the photocycle of the model membrane protein bacteriorhodopsin (bR), absorption of a photon by retinal triggers a conformational cascade that results in pumping a proton across the cell membrane. While decades of spectroscopy and structural studies have probed this photocycle in intricate detail, changes in intramolecular energetics that underlie protein motions have remained elusive to experimental quantification. Here, we measured these energetics on the millisecond time scale using atomic-force-microscopy–based single-molecule force spectroscopy. Precisely timed light pulses triggered the bR photocycle while we measured the equilibrium unfolding and refolding of the terminal 8-amino-acid region of bR’s G-helix. These dynamics changed when the EF-helix pair moved ~9 Å away from this end of the G helix during the “open” portion of bR’s pho..., , , # Dataset Overview:

This repository contains raw data files for the figures presented in \"Quantifying a light-induced energetic change in bacteriorhodopsin by force spectroscopy\" (PNAS, 2024) by David R. Jacobson and Thomas T. Perkins, including figures from the SI Appendix.

# **File Format:**

All data files are in CSV format.

Data are comma delimited.

Units are in SI, except for energies, which are in kcal/mol.

# Data Files and Descriptions:

## Fig2B.csv, Fig2C.csv

```
Description: Data from photoactivation experiments of single bR molecules.

Variables:

In Fig2B.csv

time_index: Time in seconds

Lc_4_1508_18, Lc_18_1054_22, Lc_24_887_112: Contour lengths in meters for three different molecules (destabilizing behavior)

In Fig2C.csv

time_index: Time in seconds

Lc_10_83_58, Lc_11_446_96, Lc_20_814_32: Contour lengths in meters for three different molecules (misfolding behavior)

Corresponding Figure: Fig. 2B and 2C in the paper.
```

## Fig3A.csv, Fig3B.csv

```
Des...