The motility of living organisms on the earth has been classified into 18 distinct types. Among them, class Mollicutes , consisting of parasitic bacteria such as Mycoplasma pneumoniae , has evolved unique motilities. These include gliding motility driven by F 1 -like ATPase, and swimming and coiling motilities driven by bacterial actin MreB. This study focuses on the coiling motility of Haloplasma contractile , which possesses seven MreB isoforms (MreB1-MreB7). Specific pairs—such as MreB1 and MreB2—drive coiling movement. In cells expressing the two MreBs, filamentous structures have been observed beneath the cell membrane, and these are presumed to be responsible for driving motility. Since this mechanism depends only on two small proteins, it is considered one of the minimal motility systems. The conformational changes by which these MreBs produce the coiling motility remain unclear. To investigate this mechanism, we are purifying MreB1 and MreB2 using Escherichia coli expression for structural analysis by cryo-electron microscopy. MreB1 has been successfully purified as a soluble fraction, and we are optimizing conditions for its filament formation.
Yuasa et al. (Sun,) studied this question.