UNC-104 transport properties are robust and independent of changes in its cargo binding

TL;DR

This study shows that ubiquitin-like modifications influence UNC-104 motor's cargo binding but do not affect its transport properties or distribution, highlighting robustness in motor function.

Contribution

It demonstrates that ubiquitin-like modifications alter cargo binding of UNC-104 without impacting its transport dynamics or distribution, revealing motor robustness.

Findings

Ubiquitin-like knockdowns increase UNC-104 cargo binding

Transport properties of UNC-104 remain unchanged despite modifications

Motor distribution in neurons is unaffected by ubiquitin-like modifications

Abstract

Cargo distribution within eukaryotic cells relies on the active transport mechanisms driven by molecular motors. Despite their critical role, the intricate relationship between motor transport properties and cargo binding - and its impact on motor distribution - remains inadequately understood. Additionally, improper regulation of ubiquitination, a pivotal post-translational modification that affects protein degradation, activation, and localization, is associated with several neurodegenerative diseases. Recent data showed that ubiquitination can alter motor-cargo binding of the Kinesin-3 motor UNC-104 / KIF1A that transports synaptic vesicles. To investigate how ubiquitin-like modifications affect motor protein function, particularly cargo binding, transport properties, and distribution, we utilize the PLM neuron of C. elegans as a model system. Using fluorescent microscopy, we assess the distribution of cargo-bound UNC-104 motors along the axon and probe their dynamics using FRAP experiments. We model cargo binding kinetics with a Master equation and motor density dynamics using a Fokker-Planck approach. Our combined experimental and theoretical analysis reveals that ubiquitin-like knockdowns enhance UNC-104's cooperative binding to its cargo. However, these modifications do not affect UNC-104's transport properties, such as processivity and diffusivity. Thus, while ubiquitin-like modifications significantly impact the cargo-binding of UNC-104, they do not alter its transport dynamics, keeping the homeostatic distribution of UNC-104 unchanged.