Effect of negative charge on the nuclear transport rates of biomolecules

The nucleus plays a crucial role in regulating gene expression, DNA replication, DNA repair, and cell cycle progression. The nuclear envelope is a dynamic structure that separates the nucleus from the cytoplasm and regulates the nuclear import and export of molecules via the nuclear pore complexes. The present study seeks to investigate the kinetics of transport of negatively charged graphene quantum dots and FITC dextran through nuclear membranes and quantify their transport rates and translocation characteristics. Experiments are carried out in permeabilized HeLa cells using time-lapse confocal fluorescence microscopy. Introducing negative charge onto the molecules leads to electrostatic interaction with the nuclear pore complexes, resulting in significant changes in their transport rates. We find that the negatively charged graphene quantum dots and FITC dextran have two distinct nuclear transport rates while neutral FITC dextran shows only a single transport rate. The present study shows that the mechanism of nuclear transport is not only controlled by specific sequences such as nuclear localizing signal but is also affected by the presence of charge on the molecules. We propose a model of electrostatic interaction-based transport between negatively charged cargo and positively charged FG nucleoporins to explain the results. Export studies performed after nucleocytoplasmic import confirms the bidirectionality of transport.