(111a) Autonomous Molecular Muscle with a Brake

We developed a muscle-like autonomous nanomachine that performs a stretching process upon binding a nucleic acid fuel and returns to a contracted state by a nuclease that selectively cleave the bound fuel. A prototype molecular muscle consists of two rigid terminal arms joined by a flexible connector. The addition of a fuel strand complementary to the connector sequence triggers a structural change of the connector by forming a stiff duplex, leading to an extension of the muscle device with the end-to-end distance change depending on the length of the connector. The stretching process is driven by a change in the persistence length of the connector domain from about 1 nm (three bases in the single-stranded state) to about 43 nm (100 base pairs in the double-stranded state). The contraction process involves selective digestion of a bound fuel into small fragments with a endonuclease. Because the nuclease does not cleave unbound fuels, the whole mechanical motions are autonomously recycled until the fuels are completely consumed. The molecular muscle is promising for biomedical applications to construction of nanoactuator that can provide mechanical energy to power nanodevices.