A Protocol for Regulating Protein Liquid-Liquid Phase Separation Using NMR-Guided Mutagenesis.

Liquid-liquid phase separation (LLPS) underlies the formation of membraneless cellular compartments, yet experimental strategies that directly connect quantitative LLPS behavior with residue-level structural information remain limited. Here, we present an integrated protocol that combines quantitative LLPS assays with nuclear magnetic resonance (NMR) spectroscopy and structure-guided mutagenesis to regulate protein phase separation. Using the VAPB MSP domain as a representative example, this workflow links residue-specific structural features to macroscopic LLPS behavior and enables suppression or enhancement of phase separation through targeted amino acid substitutions. This protocol provides a generalizable framework for systematic, residue-level regulation of protein LLPS.