Previous sequence alignments of Lon proteases from various bacterial species have shown that this N domain is poorly conserved and of variable length [2] and [16], yet this domain is the most stable part of the Lon protease (E. coli), as shown by both limited proteolysis and autolysis [3], [4] and [5]. For example, limited trypsin win 55 212-2 of Mycobacterium smegmatis Lon (Ms-Lon) yields a stable N-terminal fragment, which indicates that this fragment of approximately 220 residues forms an independently folded domain [13]. Mutants of Ms-Lon lacking 90–225 N-terminal residues exhibit low-level peptidase activity, and a mutant lacking 277 N-terminal residues displays neither peptidase nor ATPase activity [13]. The previous studies have suggested that the N-terminal domain of Lon plays an important role in the full function of this protease.
Fig. 1.
N-terminal amino acid sequences of Bt-Lon (Accession No. AY197372) and each N-terminal truncated mutant was constructed from the beginning of Met (●) to the amino acid position pointed out by the symbol (?) and numbered above each of the symbols.
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