An analysis of the impact of NDD and NMD-correlated DYNC1H1 mutations on dynein function

Abstract

Cytoplasmic dynein 1 is a multi-subunit protein complex involved in a wide variety of roles within eukaryotic cells. In addition to promoting nuclear migration and orienting the mitotic spindle during metaphase, dynein is the primary retrograde motor in neuronal cells, responsible for transporting cargo from the tip of the axon to the soma along the microtubule network. These cargoes range from aggregates of misfolded proteins, to mRNA transcripts, to an array of biomolecules providing nutrients to the cell (Schiavo et al., 2013). Any defect in these processes will affect a cell's ability to survive, proving particularly detrimental within the class of neurons devoted to motor function. Many previous studies have linked mutations of the dynein heavy chain, which houses the motor domain, to various neurodevelopmental and neuromuscular diseases (NDD and NMDs, respectively). The associated dysfunction can range from mild neuropathy to severe cases of intellectual impairment (Becker et al., 2020). To understand the molecular basis for such diseases, we developed and tested nine disease-correlated point mutations of the dynein heavy chain in a budding yeast system. Although dynein's roles in yeast are limited to mitotic spindle positioning, our results provide insight into the relative impact of each mutation on dynein functionality and motor complex activity. Both G2418V and W1445R dynein mutants exhibited severe dysfunction, with a significant reduction recorded in all observed motility and activity parameters. Another mutation, G2181E, was shown to correlate with dynein dysfunction of similar magnitude to the dynein knockout control. However, molecular dynamics simulations suggest that the effects of G2181E may be reversed via a "rescue" substitution at the interacting residue K1560.