Figure 4 - The fungal FAS is another biomolecular motor.

(a) The central wheel of the ₆₆ heterododecameric FAS from T. lanuginosus. (b) The fungal FAS contains two reaction chambers, one above and the other below the central wheel, each containing three sets of active sites. The ACP domain (shown in blue) encircles the catalytic domains, rotating about two fixed anchor points through flexible peptide linkers. Domains from the -chains are shown in pink and blue, and domains from the -chains are shown in green, yellow and gray. (c) The circular motion of the ACP perpendicular to the vector connecting the anchor points resembles the motion of the 'flyballs' in the centrifugal governor designed by James Watt in 1788, which was used to control the speed of a steam engine. In this sense at least the fungal FAS could be considered to be a biomolecular motor, in which the negative free energy of the reactions catalyzed by the FAS drives the motion of the ACP in a fashion similar to the way that ATP hydrolysis provides the mechanical driving force for the ATPase and DNA helicase motors. Panels a and b from ref. 42. Reprinted with permission from AAAS. Panel c adapted with permission from Encyclopædia Britannica, copyright 1996 by Encyclopædia Brittanica, Inc.