Wednesday, 13 May 2015
Dynein: Tiny Tightrope Walking Machine in Our Cells
Hardly a week goes by without a paper on molecular machines being published in a major science journal. Recently, PNAS published a study on the cytoplasmic dynein, which transports cargo by walking along a microtubule.
Fine-tuning is very much evident in its walk:
“Cytoplasmic dynein is the primary minus-end–directed microtubule (MT) motor. It is unclear how dynein coordinates ATP hydrolysis and MT attachment within and between its two motor domains, each containing four AAA+ ATPases (AAA: ATPase associated with various cellular activities), AAA1–4. We characterize how mechanical tension and nucleotide states of AAA1 and AAA3 regulate dynein–MT binding. Dynein binds MTs tighter when subjected to tension opposite its normal motility. ADP binding to AAA3 unexpectedly weakens MT-binding strength and reduces the bond strength anisotropy. Finally, AAA3 'gates' the activity of AAA1: ATP binding to AAA1 induces MT release only if AAA3 contains nucleotide. This work expands understanding of the role of force in dynein mechanochemistry and identifies regulatory functions of AAA3.”
A kinesin motor does practically the same thing, but in the opposite or plus-end direction. Both the dynein and kinesin suggest that our cells work in anything but a haphazard way.
In other words, fine-tuning and amazing design are evident from start to finish.
Nicholas, Matthew P. et al. 2015. Cytoplasmic dynein regulates its attachment to microtubules via nucleotide state-switched mechanosensing at multiple AAA domains. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1417422112