ATP-Dependent LonBA Proteases of Bacilli and Clostridia

Objective: ATP-dependent Lon proteases are key players in the quality control system of cellular proteins. The Lon family includes three main subfamilies (A, B, and C), whose representatives are common in bacteria, eukaryotes, and archaea. Recently, enzymes that potentially form a new “hybrid” subfamily LonBA have been discovered in bacteria of the Bacilli and Clostridia classes. This study aims to characterize the structure of LonBA proteases and elucidate their features by comparison with classical LonA and LonB proteases. Methods: Bioinformatics analysis methods and approaches were used to comparatively characterize Lon proteases of different subfamilies. Results and Discussion: Analysis of sequences of the common pool of Firmiqutes’ Lons showed that they contain both classical LonA and “hybrid” LonBA proteases. The ATPase component of the latters is similar to the ATPase fragment of LonB proteases, while the catalytic P domain is similar to the P domain of LonA proteases. Degrees of similarity of different structural fragments of LonBAs were estimated. Groups of short and long LonBA proteases were identified. Sources of short-LonBAs are both bacilli and clostridia, but long ones—only clostridia. Conclusions: The new subfamily of LonBA proteases was shown to consist of two communities of enzymes that differ in the structure of their N-terminal fragments and protease domains.