New Insights into Cellular Transport Mechanisms

Author: ChemistryViews
Published On: August 4, 2024
Copyright: Wiley-VCH GmbH

Cytoplasmic dynein is a motor protein essential for transporting materials within cells. Despite being well-studied in laboratory settings, its behavior in live cells remains unclear.

Steven Chu, Stanford University, CA, USA, and colleagues have developed highly photostable rare-earth ion-doped upconverting nanoparticles (UCNPs) for long-term single-particle tracking in live cells. These probes allowed them to observe dynein’s movement in neuronal axons. The team tracked the dynein transport of twelve individual cargos over 900 μm for tens of minutes. The researchers discovered that the number of active dynein motors involved in moving a cargo fluctuates between one and five during transport in neuronal axons.

Using the bright optical probes, the researchers were also able to resolve individual molecular steps in living cells. They found that each dynein step involves the sequential hydrolysis of two ATP molecules. The dwell times between steps are controlled by two temperature-dependent rate constants. This uncovers a previously unknown chemomechanical cycle of dynein-mediated cargo transport in living cells.

However, the researchers say that the molecular details of how dynein causes a vesicle to move during the hydrolysis cycle remains unclear. They plan to address the microscopic molecular nature of how motors advance on microtubules in future research.

The UCNPs

The researchers created 23 nm β-NaYF₄ nanoparticles codoped with 20% Yb³⁺ and 2% Er³⁺ and coated them with a 5 nm silicon dioxide layer. This allowed the formation of monodispersed UCNPs in aqueous solution, facilitating direct conjugation with silane derivatives like silane-polyethylene glycol (PEG500) to reduce nonspecific binding and silane–PEG3400–biotin for targeting, with no observable cytotoxicity.