Molecular Matchmakers: How ATP and Small Amphiphilic Molecules Fine-Tune FET Proteins Clusters

FET (FUS-EWSR1-TAF15) family proteins inherently form mesoscale molecular assemblies, known as clusters, under physiological conditions at concentrations well below the threshold for phase separation. This study demonstrates that adenosine triphosphate (ATP), an amphiphilic molecule and essential cellular metabolite, modulates the size of these sub-saturation mesoscale clusters in a concentration-dependent manner. At low concentrations (1-2 mM), ATP acts as a crosslinker for FET proteins, resulting in larger size clusters. At moderate concentrations (5 mM), the size of the clusters decreases but stabilizes. At high concentrations (10 mM), the cluster size further diminishes. Other amphiphilic molecules, including common hydrotropes like sodium xylene sulfonate, sodium toluene sulfonate, and hexanediol, exhibit comparable concentration-dependent effects on FET protein clustering. Notably, these effects cannot be explained solely by hydrotropic or kosmotropic mechanisms; instead, they stem from non-specific interactions between proteins and small molecules. The intrinsic chemical properties of the amphiphilic molecules and FET proteins play a crucial role in regulating mesoscale cluster formation at sub-saturation concentrations. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=99 SRC="FIGDIR/small/649119v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@90de68org.highwire.dtl.DTLVardef@f9bcb5org.highwire.dtl.DTLVardef@1d42e59org.highwire.dtl.DTLVardef@12eed97_HPS_FORMAT_FIGEXP M_FIG C_FIG