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Dendrimers

Sticky situation

The sliding movement of the actin–myosin protein conjugate responsible for contracting muscles can be inhibited using a dendrimer that glues them together.

Credit: © 2010 WIley

Muscles contract because of the concerted molecular-level interactions between numerous actin and myosin proteins that work together to shorten muscle fibre. Myosin acts like an active ratchet, which binds to a filament of actin, pulls it in one direction, lets go, and then realigns itself before binding again. ATP drives the process and, in particular, it binds to myosin, which reduces the affinity of myosin for binding with actin, causing the two proteins to detach.

Now Takuzo Aida, Kazushi Kinbara and colleagues at the Universities of Tokyo and Tohoku have shown1 that this process can be hindered or completely stopped by 'gluing' the proteins together with a dendrimer that binds to both actin and myosin. The dendrimer is made up of ether branches and is terminated with nine guanidinium ions, which can bind to the oxyanions prevalent on protein surfaces.

To show that it could bind to both proteins and arrest the motion of actin, Aida, Kinbara and colleagues attached numerous myosin proteins to a surface and observed the behaviour of fluorescently tagged actin molecules when added to the mix. When no dendrimer was present the actin filaments moved with a velocity of approximately 4.6 μm s−1 but when the dendrimer was added, their motion stopped completely. A lower-generation dendrimer with only three guanidinium-terminated branches does not act like a molecular glue, so it seems that the number of sites on the dendrimer that can interact with the proteins is key to its ability to bind two proteins simultaneously.

References

  1. Okuro, K. et al. Adhesion effects of a guanidinium ion appended dendritic “molecular glue” on the ATP-driven sliding motion of actomyosin. Angew. Chem. Int. Ed. 10.1002/anie.200906139 (2010).

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Armstrong, G. Sticky situation. Nature Chem (2010). https://doi.org/10.1038/nchem.647

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  • DOI: https://doi.org/10.1038/nchem.647

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