Structural insights of the human R7BP-Gβ5-RGS7 complex using cross-linking mass spectrometry

Authors

• PR Adikaram
• JH Zhang
• WF Simonds

Abstract

The R7-RGS/Gß5 protein duplex functions as a GTPase-activating protein (GAP) to facilitate the Gai/o intrinsic GTPase activity. The R7-RGS subfamily of RGS (Regulator of G protein Signaling) proteins comprises RGS6, RGS7, RGS9 and RGS11. The RGS7-binding protein (R7BP) anchors the R7-RGS/Gß5 duplex to the cell membrane to enhance its GAP activity. Recently it was shown that knock-out of R7BP in mice led to decreased itch sensation, indicating that R7BP has a central role in itch response. To inhibit itch, we are developing interfering peptides to block the R7BP and R7-RGS/Gß5 interactions. As only the mouse RGS9/Gß5 crystal structure has been solved, we use cross-linking mass spectrometry (XL-MS) to obtain structural clues about the human RGS7/Gß5/R7BP triplex. To this end, we transfected the three plasmids into Expi293 cells and purified the protein triplex to 95% purity. The triplex was cross-linked using the reagent DSSO (disuccinimidyl sulfoxide) at 1:100 and 1:300 protein:DSSO molar ratios and analyzed by mass spectrometry. The experiment was repeated using the human RGS9/Gß5/R7BP triplex. Both experiments yielded peptides involved in the RGS7/9-R7BP interaction, with one R7BP peptide common to both. We believe this peptide region is an essential interaction surface on R7BP and an ideal target for peptide design to block interaction between R7BP and RGS proteins. We are currently working to confirm these interactions using X-ray crystallography structure data. Taken together, we demonstrate that XL-MS is an effective way to shed light on structural features of the R7-RGS/Gß5/R7BP triplex to facilitate the development of novel anti-itch drugs.

Scientific Focus Area: Structural Biology

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