| Summary: | 碩士 === 臺灣大學 === 生化科學研究所 === 98 === The Lon proteases had been known as one of the most evolutionarily conserved proteins. According to previous findings, Lon proteases possessed ATPase, protease, peptidase and chaperone activities. Based on these multi-functional Lon proteases, the protein quality control system and the regulation of metabolic process could both work well. In this study, the function-structural characterizations among Mt-LonA1, Mt-LonA2 and Mt-TTC1975 from Meiothermus taiwanensis would be juxtaposed to express the contrast.
The Lon protease family could be divided into two subfamilies, LonA and LonB, mainly based on the sources and the domain structures of these proteins. The LonA consisted of a variable N-terminal domain (N domain), a central ATPase domain (A domain), and a C-terminal protease domain (P domain) on a single polypeptide. Depending on the analysis of primary structures of Mt-LonA1, Mt-LonA2 and Mt-TTC1975, This study considered that Mt-LonA1 and Mt-LonA2 both should be classified as the LonA subfamily, for Mt-LonA1 and Mt-LonA2 both possessed the classical LonA-type domains. For Mt-TTC1975, it only possessed a high similarity in protease domain with canonical LonA. Therefore, it should not be classified as the Lon protease.
Structural characteristic results by circular dichroism showed that Mt-LonA1, Mt-LonA2 and Mt-TTC1975 possessed mostly α-helical secondary structures and they all possesed well-defined three-dimensional structures. For quaternary structures, the AUC data, Native-PAGE and EM graph revealed that Mt-LonA1 functions mainly as a hexamer; the AUC data and Native-PAGE revealed that Mt-LonA2 might function as a mixture of dimer and pentamer; Native-PAGE revealed that Mt-TTC1975 functions as a hexamer or a heptamer.
Functional characteristic results showed that Mt-LonA1 exhibited the ATPase, protease, peptidase and chaperone activity; Mt-LonA2 exhibited the ATPase, protease, peptidase and DNA-binding activity; Mt-TTC1975 exhibited the chaperone activity only.
Lastly, the comparison of primary structure of α-domains and the results of homology modeling suggested that the K527 residue and the K-K-R conserved region of Mt-LonA2 might critically influence the DNA-binding activity.
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