Profiling calcium-dependent interactions between Sorcin and intrinsically disordered regions of human proteome

Background: Sorcin is a calcium sensor that exerts many calcium-related functions in the cells, e.g. it regulates calcium concentration in the cytoplasm, endoplasmic reticulum (ER) and mitochondria, by interacting with calcium pumps, exchangers and channels. Albeit Sorcin is an interesting potential cancer target, little is known about its interactors upon calcium-mediated activation. Our previous study suggested that Sorcin may recognize short linear binding motifs as the crystal structure revealed a self-interaction with a GYYPGG stretch in its N-terminus, and combinatorial peptide-phage display provided support for peptide-mediated interactions. Methods: In this study we screened for motif-based interactions between Sorcin and intrinsically disordered regions of the human proteome using proteomic peptide phage display (ProP-PD). We identified a peptide belonging to protein phosphatase 1 regulatory subunit 3G (PPP1R3G) as a potential novel interactor and confirm the interaction through biophysical and cell-based approaches, and provide structural information through molecular dynamics simulations. Results: Altogether, we identify a preferred motif in the enriched pool of binders and a peptide belonging to protein phosphatase 1 regulatory subunit 3G (PPP1R3G) as a preferred ligand. Conclusion: Through this study we gain information on a new Sorcin binding partner and profile Sorcin's motif-based interaction. General significance: The interaction between Sorcin and PPP1R3G may suggest a close dependence between glucose homeostasis and calcium concentration in the different cell compartments, opening a completely new and interesting scenery yet to be fully disclosed.