Abstract
We identified a TTC1975-like protein from the thermophile Meiothermus taiwanensis WR-220 as a homolog of the protease domain of Lon protease. The lack of the ATPase domain excludes this protein, Mtw-TTC, from the AAA+ superfamily, even though Mtw-TTC possesses the conserved Ser-Lys dyad and TTC1975 proteins are classified as a member of the Lon protease family (S16) in the MEROPS database. We cloned, over-expressed and characterized Mtw-TTC. Far-UV CD measurements showed that Mtw-TTC consists of α-helices as the major secondary structure. Sedimentation velocity analysis indicated that the protein forms a 42S complex in solution. Gel-filtration chromatography revealed a major fraction near 2,000 kDa and a minor fraction of 481 kDa, which was confirmed by cryo-fixation transmission electron microscopy and native PAGE. In transmission electron micrographs, Mt-TTC was composed of hexamers and heptamers, owing to the dissociation of the 42S assembly in low pH buffer. Mtw-TTC was stable below 74 °C and displayed chaperone activity with chemically stressed or UV-irradiated proteins. Our results support a role of Mtw-TTC in the chaperone network of M. taiwanensis.
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