MSC Thesis Presentation: Solid State NMR Study of New Sensory Rhodopsin (SR138)

MSc Candidate

Sajjad Salimi Nanehkarani

Abstract

In our investigation of SR138, a proteobacterial sensory rhodopsin homolog from saline environments and part of the Proteo-SRs group, we aimed to elucidate its structure and evolutionary ties to proteorhodopsins (PRs) using solid-state NMR. Our study achieved several positive outcomes, including high levels of protein expression and functionality, alongside acceptable resolution in our spectra. We employed advanced NMR techniques, such as 1D ¹⁵N, 2D ¹³C-¹³C, 3D NCACX, CANCO, NCOCX, and 4D CONCACX and CANCOCX, allowing us to achieve partial assignments of the protein resonances. Our initial characterization identified the secondary structure elements, notably helical structures and specific beta sheet configurations within the BC loop. These findings lay a solid foundation for further methodological improvements and optimizations. Despite these successes, we faced hurdles due to unresolved spectra and numerous overlapping regions, which limited our ability to assign a more extensive range of amino acid residues during the backbone walking process. This challenge underscores the complex nature of SR138 and indicates areas for future focus, including the exploration of reverse-labeling and sparse labeling techniques to enhance assignment capabilities. Our study not only contributes to the understanding of SR138 but also sets the stage for advancing the structural analysis of similar membrane proteins.

Examination Committee

• Dr. Hermann Eberl, Chair 
• Dr. Vladimir Ladizhansky, Advisor 
• Dr. Leonid Brown, Advisory Committee 
• Dr. Robert Wickham, Graduate Faculty