Diffuion Behavior of Supuramolecular Protein Assemblies in the Living Cell Nucleus

Abstract

Cell nucleus is filled with chromatin which has uncondensed polymeric conformation without intermolecular entanglement. In spite of the lack of the entanglement, chromatin is compartmentalized in highly organized manner. Previous studies revealed that the chromatin moves coherently with long-range correlations on the scale of microns. The spatiotemporal organization remains an open question in cell biology. To elucidate such long scale motion under highly organized structural regularity, we need to know its viscoelasticity in micro and meso scales. However, we have only limited measurement methods for the viscoelasticity of confined in such narrow space. One useful method for measuring the viscoelasticity is the particle tracking, which extract shear moduli by analyzing diffusive motion of particles embedded in the medium. However, injecting particles inside the nucleus induces serious stress to the cell. To perform the particle tracking in the living cell nucleus without any stress, we need a natural probes. In this study, we use genetically encoded supramolecular protein assemblies as natural probes [Bellapdorona et al., Angew. Chem. Int. Ed. 2014, 53, 1534]. Expressed supramolecular protein assemblies form spherical aggregates with a diameter of 0.5 - 1.0 micron in the nucleus. Particle tracking method reveals that the protein assemblies show an anomalous diffusion at short time range but shifts to the normal Brownian motion at long time range. Our study presents a noninvasive approach of using a supramolecular protein assemblies and their dynamics to investigate material properties of the living cell nucleus. Our natural probes enable to analyze the local diffusion behavior in the living cell nucleus without causing damage to the cell.