Biophysics of Complex Systems (BIOSYS) Team of ISA, Lyon

The Biosys team is interested in protein dynamics and their interactions. To this end, it uses various biophysical methods coupled with molecular dynamics simulations.

We used the Infranalytics NMR facilities at very high fields 900 and 1200 MHz in Lille. We implemented a series of spin relaxation measurements based on the observation of longitudinal and transverse relaxation. ¹⁵N as well as heteronuclear NOEs ¹H-¹⁵N. These measurements were combined with those carried out using our local means (400 and 600 MHz). These spin relaxation experiments provide access to the local and global dynamics that characterize proteins in the ps-ns range. However, the determination of dynamic parameters such as order parameters (S²), correlation time (t_c) or even fast correlation time (t_almost) are obtained under a number of assumptions. One of these is to use an average value for the chemical shift anisotropy (CSA) rather than assigning a unique value to each ¹⁵N. This approximation is justified for fields up to 600 MHz but can cause a significant bias in the exploitation of relaxation data at very high fields.

Using a model protein such as ubiquitin and combining the measurements obtained with four magnetic fields, we determined the values ​​of the chemical shift anisotropy (¹⁵N-CSA) for each residue. Using a uniform value of -160 ppm causes significant fluctuations in the values ​​of the order parameter (S²) as a function of the magnetic field. Conversely, using a CSA value specific to each residue considerably reduces these fluctuations. It is then possible to substitute a series of measurements at several fields by the combination of a measurement at a single field and molecular dynamics simulations to obtain similar results for S².

More: 10.1039/d4cp03821e

Platform used: IMEC - ISB - UCCS Lille