One amazing molecular machine is ATP synthase.
It operates in a rotational catalysis mechanism. The β subunits perform the catalysis of ADP + Pi -> ATP. The γ subunit is responsible for rotating the β subunits and is driven by the influx of Hydrogen ions.
As the β subunits are rotated their conformation changes depending on their contacts with the γ subunit. Firstly ADP and Pi are bound loosely within one β subunit. The rotational conformation change then produces ATP by binding the reactants tightly and stabilizing the ATP form. In the next rotation, the ATP molecule is only loosely bound by the β subunit and the molecule can dissociate. There are many videos of this process available on Youtube.
This synthase is a great example of both a cyclic machine (10.1.1) and an enzyme catalyses a reaction by binding to the transition state (10.3.3). Can you think of any other examples?
(Information taken from textbook: Lehninger- Principles of Biochemistry
Image from article: Molecular Motors: Turning the ATP motor, Richard L. Cross, Nature 427, 407-408(29 January 2004), doi:10.1038/427407b)