Bidirectional protein-protein interactions control liquid-liquid phase separation of PSD-95 and its interaction partners

Nikolaj Riis Christensen; Christian Parsbæk Pedersen; Vita Sereikaite; Jannik Nedergaard Pedersen; Maria Vistrup-Parry; Andreas Toft Sørensen; Daniel Otzen; Kaare Teilum; Kenneth Lindegaard Madsen; Kristian Strømgaard

doi:10.1016/j.isci.2022.103808

Bidirectional protein-protein interactions control liquid-liquid phase separation of PSD-95 and its interaction partners

iScience. 2022 Jan 25;25(2):103808. doi: 10.1016/j.isci.2022.103808. eCollection 2022 Feb 18.

Affiliations

¹ Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.
² Department of Neuroscience, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
³ Structural Biology and NMR Laboratory & the Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark.
⁴ Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.

Abstract

The organization of the postsynaptic density (PSD), a protein-dense semi-membraneless organelle, is mediated by numerous specific protein-protein interactions (PPIs) which constitute a functional postsynapse. The PSD protein 95 (PSD-95) interacts with a manifold of proteins, including the C-terminal of transmembrane AMPA receptor (AMPAR) regulatory proteins (TARPs). Here, we uncover the minimal essential peptide responsible for the Stargazin (TARP-γ2)-mediated liquid-liquid phase separation (LLPS) formation of PSD-95 and other key protein constituents of the PSD. Furthermore, we find that pharmacological inhibitors of PSD-95 can facilitate the formation of LLPS. We found that in some cases LLPS formation is dependent on multivalent interactions, while in other cases short, highly charged peptides are sufficient to promote LLPS in complex systems. This study offers a new perspective on PSD-95 interactions and their role in LLPS formation, while also considering the role of affinity over multivalency in LLPS systems.

Keywords: Biomolecules; Biophysics; Pharmacology; molecular biology; molecular neuroscience.