2021 Virtual Undergraduate Research Symposium
2021 Virtual Undergraduate Research Symposium
The Role of the Conserved Disulfide Bond in G Protein Coupled Receptors
The Role of the Conserved Disulfide Bond in G Protein Coupled Receptors
3RD PLACE POSTER
PROJECT NUMBER: 15 | AUTHOR: Varsha Selvam, Chemical and Biological Engineering
MENTOR: Judith Klein-Seetharaman, Chemical and Biological Engineering
ABSTRACT
Rhodopsin is a member of the pharmaceutically important G Protein Coupled Receptor (GPCR) family and plays a critical role in converting light into electrical signals. Rhodopsin misfolding has also been associated with Retinitis Pigmentosa (RP). RP is a degenerative disorder that severely impairs vision. Mutations occurring in the transmembrane and intradiscal domains make up a majority of the mutations that lead to RP. Studies on these mutations support that a disulfide bond different from that of the native one is found in the mutated proteins. To test the generality of this finding for the GPCR family, we tested the extent to which the disulfide bond found between Cysteine 110 towards the bottom of the helix and the Cysteine 187 in the second extracellular loop is conserved. We found that the extent of conservation depends on the GCPR subfamily. While the disulfide bond is critical in stabilizing rhodopsin, structural analysis of other GPCRs suggests that it is not the properties of the bond or the surrounding structure that helps stabilize Rhodopsin. Instead, we propose based on the flexibility ratio of interhelical loops, that perhaps the disulfide bond plays a role in the unstretched loop connecting the fourth and fifth transmembrane regions, providing a structural constraint in the folding of rhodopsin and GPCRs in general.
PRESENTATION
AUTHOR BIOGRAPHY
Varsha Selvam is a senior in the Chemical and Biological Engineering department at Mines. She pursues a major in Chemical Engineering with a biological focus and a minor in Biomedical Engineering. Currently, she is conducting research under Dr. Judith Klein-Seetharaman. The research project explores the role of a disulfide bond in GPCRs. Varsha looks forward to pursuing her Master’s degree in Engineering and Technology Management in the fall.
Hi Varsha, great presentation! I have a question on the flexibility ratio. How are the distances associated with this ratio measured?
Hi Roger, thank you for your question. The flexibility ratio is composed of d, the distance between the α-carbons of the first and last residues of the loop in the x-ray structure, and l, the length of the loop segment if it were removed from the protein and fully stretched. “d” is determined by using software tools such as Pymol, and when choosing the alpha carbons of interest, the distance between them is outputted. This resource provides additional insight as to how the α-carbons can be chosen (https://www.cell.com/biophysj/fulltext/S0006-3495(09)00307-5). As for the length the expressions, a(n/2 − 1) +b and a(n − 1)/2 for even and odd n (number of residues) were used. In Flory’s book, the following parameters were found: a= 6.046 and b = 3.46 Å. More information on these expressions can also be found in the resource above. Please let me know if you have any other questions!
Nice work, Varsha! Is it known how rhodopsin misfolding affects its photosensitive properties?