https://doi.org/10.1101/2025.04.18.647244
요약
- Prion-like domain (PLD)를 가진 단백질의 응축체가 stress granule 형성에 기여: G3BP1 없이도, PLD를 포함한 FUS, TIA1, hnRNPA1 등의 단백질은 stress granule-like condensate를 형성하고 세포 내 SG assembly에 기여함.
- Condensate가 stress granule을 물리적으로 ‘씨앗(seed)’함: PLD 응축체는 주변 mRNA와 단백질을 끌어들여 stress granule의 형성과 성장을 유도하며, 특히 PLD와 interaction이 강한 단백질들이 선별적으로 농축됨.
- Stress granule persistence에 결정적인 역할: PLD 기반 응축체가 존재할 경우, stress 조건이 해제된 후에도 stress granule이 장시간 지속(persistent)되는 특성을 보임.
- Reentrant phase separation으로 세포 내 응축체 조절 가능: RNA 농도가 증가하면 initially 응축체가 생성되지만, 과잉 RNA는 되려 해체를 유도하는 reentrant behavior도 관찰됨.
- PLD 응축체의 조성 변화가 LLPS 및 응축체 기능을 제어: Tyrosine(Y)-rich PLD는 π–π interaction이 중심이며, 이는 단백질 농축 및 stress granule의 물리적 특성 조절에 핵심적으로 작용.
Abstract
Protein condensation is the basis for formation of membrane-less organelles in the cell. Most famously, weak, polyvalent interactions, often including RNA, may lead to a liquid-liquid phase separation. This effect greatly enhances local concentrations and is thought to promote interactions that would remain rare in dilute solution. Synthetic systems provide a means to clarify the underlying biophysical mechanisms at play, both in vitro and in the cell via exogenous expression. In this regard, ferritin is a useful substrate, as its composition of 24 subunits with octahedral symmetry supports self-assembly by close packing in 3D. The conventional diagnostic tool for protein condensation is fluorescence imaging. In this work we explore the use of refractive index mapping to detect states of condensation and decondensation. Using two related ferritin-based self-assembly systems, we find that refractive index is a sensitive indicator for reversible condensation. Surprisingly, refractive index indicates a rapid decondensation even when molecular dispersal kinetics are slow according to fluorescence. Conversely, in a photo-activated condensation where long activation results in slow decondensation kinetics, the refractive index provides reliable evidence for the physical state independent of fluorescence. The observations suggest a distinction between condensation to a sparse biomolecular network, or to a material continuum that supports an optical polarizability distinct from that of the dilute phase in solution.