Single-Molcule Studies on DNA Transportation Motors with Common Revolution Mechanism without Rotation

Abstract

Nucleic acid translocation is ubiquitous in living systems. The motion required for these events is accomplished by biomotors that hydrolyze ATP. Biomotors were once classified into two categories: linear and rotation motors. Recently, a third class of motor employing a revolution mechanism without rotation was reported. While rotation involves spinning of an object around its own axis, revolution is the circular movement of an object around a secondary center-object. By analogy, rotation resembles the Earth's motion about its axis once every 24 hours, whereas revolution resembles the Earth ‘circling’ around the Sun once every 365 days.The rotation and revolution mechanisms can be distinguished by the size of channel and the chirality of the channel wall. The channels of rotation motors are equal to or smaller than 2 nm, that is the size of dsDNA, whereas channels of revolution motors are larger than 3 nm. Rotation motors use parallel threads to operate with a right-handed channel, while revolution motors use a left-handed channel to drive the right-handed DNA in an anti-chiral arrangement. This revolving biomotor was found to be widespread among many biological systems, including dsDNA viruses, dsDNA bacteriophages, bacteria, and archaea.We here present biophysical studies using single-molecule fluorescence and magnetic tweezers, as well as biochemical analysis and structural comparison to illustrate the main features of this newly discovered revolution mechanism on example of the Phi29 bacteriphage DNA packaging motor.