Michael Lin, Postdoctoral Faculty Sponsor
Client proximity enhancement inside cellular membrane-less compartments governed by client-compartment interactions
2020; 11 (1): 5642
Membrane-less organelles or compartments are considered to be dynamic reaction centers for spatiotemporal control of diverse cellular processes in eukaryotic cells. Although their formation mechanisms have been steadily elucidated via the classical concept of liquid-liquid phase separation, biomolecular behaviors such as protein interactions inside these liquid compartments have been largely unexplored. Here we report quantitative measurements of changes in protein interactions for the proteins recruited into membrane-less compartments (termed client proteins) in living cells. Under a wide range of phase separation conditions, protein interaction signals were vastly increased only inside compartments, indicating greatly enhanced proximity between recruited client proteins. By employing an in vitro phase separation model, we discovered that the operational proximity of clients (measured from client-client interactions) could be over 16 times higher than the expected proximity from actual client concentrations inside compartments. We propose that two aspects should be considered when explaining client proximity enhancement by phase separation compartmentalization: (1) clients are selectively recruited into compartments, leading to concentration enrichment, and more importantly, (2) recruited clients are further localized around compartment-forming scaffold protein networks, which results in even higher client proximity.
View details for DOI 10.1038/s41467-020-19476-4
View details for Web of Science ID 000591592300010
View details for PubMedID 33159068
View details for PubMedCentralID PMC7648067
Behavior control of membrane-less protein liquid condensates with metal ion-induced phase separation
2020; 11 (1): 5554
Phase separation of specific biomolecules into liquid droplet-like condensates is a key mechanism to form membrane-less organelles, which spatio-temporally organize diverse biochemical processes in cells. To investigate the working principles of these biomolecular condensates as dynamic reaction centers, precise control of diverse condensate properties is essential. Here, we design a strategy for metal ion-induced clustering of minimal protein modules to produce liquid protein condensates, the properties of which can be widely varied by simple manipulation of the protein clustering systems. The droplet forming-minimal module contains only a single receptor protein and a binding ligand peptide with a hexahistidine tag for divalent metal ion-mediated clustering. A wide range of protein condensate properties such as droplet forming tendency, droplet morphology, inside protein diffusivity, protein recruitment, and droplet density can be varied by adjusting the nature of receptor/ligand pairs or used metal ions, metal/protein ratios, incubation time, binding motif variation on recruited proteins, and even spacing between receptor/ligand pairs and the hexahistidine tag. We also demonstrate metal-ion-induced protein phase separation in cells. The present phase separation strategy provides highly versatile protein condensates, which will greatly facilitate investigation of molecular and structural codes of droplet-forming proteins and the monitoring of biomolecular behaviors inside diverse protein condensates.
View details for DOI 10.1038/s41467-020-19391-8
View details for Web of Science ID 000591843300009
View details for PubMedID 33144560
View details for PubMedCentralID PMC7642319
Homo-molecular Fluorescence Complementation for Direct Visualization of Receptor Oligomerization in Living Cells
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
2019; 58 (7): 2045-2049
Cell surface receptor oligomerization is an attractive target process for drug screening. However, simple but reliable (and thus high-throughput) visualization methods for receptor oligomerization are still lacking. Herein, we report on a new single-construct homo-molecular fluorescence complementation (Homo-FC) probe, which shows strong fluorescence signals by oligomerization of fused receptors in living cells with unexpectedly low background signals. Importantly, this high signal-to-noise ratio was not affected by expression level variations of fused receptors. The Homo-FC probe was developed by optimized flopped fusion of split fragments of superfolder green fluorescence protein and subsequent surface charge engineering. Homo-FC reliably visualized the oligomerization of diverse natural receptors such as GPCR, EGFR, and even cytosolic DAI.
View details for DOI 10.1002/anie.201812780
View details for Web of Science ID 000458828000028
View details for PubMedID 30561874