Certain properties and functions of membraneless organelles (MLOs) have been linked to diseases such as neurodegenerative disorders and cancer, and being able to quantify the factors that affect these properties can lead to a better understanding of how to treat and prevent these conditions. The production of protein-RNA condensates in a laboratory, which mimic the properties of MLOs, helps researchers study the interactions between condensate components and the associated fluid dynamics. Researchers from the University at Buffalo have used lab-made biocondensates and microrheology with optical tweezers to uncover how the specific amino acids within the droplets impact their viscous and elastic properties.
Passive microrheology with optical tweezers (pMOT) was used to measure the viscoelasticity of a series of lab-made droplets, which were formed by disordered sticker-space polypeptides and RNA. The researchers found that the condensates exhibited the properties of a Maxwell fluid: at shorter timescales, the condensates behaved more like elastic solids, while at longer timescales, they acted more as viscous liquids.
Further experiments testing the incorporation of different peptide sequences revealed that the placement of specific sticker and spacer residues within the sequences resulted in more elastic or more viscous properties, allowing for the overall viscoelasticity to be programmed by tuning these amino acid placements. This study was published in Nature Communications.
“It may seem like a small change to replace just a single amino acid in the entire peptide sequence. Yet, our computer simulations show that some amino acids are way ‘stickier’ when it comes to binding to RNA molecules,” said Davit A. Potoyan, one of the paper’s corresponding authors. “This differential stickiness at microscopic scales then propagates to create large-scale changes in the fluid properties of condensates. That’s the main story of this research.”
Quantifying viscoelasticity in MLOs using methods such as those described in the study can help to further identify how factors such as mutations and aging impact the properties and functions of these biocondensates, said fellow corresponding author Priya R. Banerjee. Further understand of these dynamics can bring scientists closer to combatting certain disease processes.
Photo: Bright-field image of micron-scale viscoelastic protein-RNA droplets. Credit: Ibraheem Alshareedah/Banerjee Lab