Functional mechanics of the ATP-dependent Lon protease- lessons from endogenous protein and synthetic peptide substrates

Abstract

Lon, also known as the protease La, is a homo-oligomeric ATP-dependent protease, which is highly conserved in archaea, eubacteria and eukaryotic mitochondria and peroxisomes. Since its discovery, studies have shown that Lon activity is essential for cellular homeostasis, mediating protein quality control and metabolic regulation. This article highlights the discoveries made over the past decade demonstrating that Lon selectively degrades abnormal as well as certain regulatory proteins and thus plays significant roles in maintaining bacterial and mitochondrial function and integrity. In addition, Lon is required in certain pathogenic bacteria, for rendering pathogenicity and host infectivity. Recent research endeavors have been directed toward elucidating the reaction mechanism of the Lon protease by different biochemical and structural biological techniques. In this mini-review, the authors survey the diverse biological roles of Lon, and also place special emphasis on recent findings that clarify the mechanistic aspects of the Lon reaction cycle.

Figure 1

Domain organization for a subunit in Lon protease.

Figure 2

The degradation profile of λN and the sequence of the peptide substrate derived from the Lon cleavage profile of λN. Figure 2A shows the primary sequence of the λN protein, with the Lon cleavage sites underlined. Figure 2B shows the sequence of the fluorogenic peptide used for monitoring the ATP-dependent peptidase activity of Lon. This peptide contains residues 89–98 of the λN protein, the fluorophore Abz and the fluorescence quencher nitrotyrosine. An increase in the Abz fluorescence is detected upon peptide cleavage by Lon in the presence of ATP.

Figure 3

Kinetic model to account for the ATP-dependent cleavage of FRETN 89–98 by E. coli Lon.

Figure 4

Structures of peptide boronate inhibitors against Lon proteases.