Structure of the catalytic domain of the human mitochondrial Lon protease: Proposed relation of oligomer formation and activity

Abstract

ATP-dependent proteases are crucial for cellular homeostasis. By degrading short-lived regulatory proteins, they play an important role in the control of many cellular pathways and, through the degradation of abnormally misfolded proteins, protect the cell from a buildup of aggregates. Disruption or disregulation of mammalian mitochondrial Lon protease leads to severe changes in the cell, linked with carcinogenesis, apoptosis, and necrosis. Here we present the structure of the proteolytic domain of human mitochondrial Lon at 2 Å resolution. The fold resembles those of the three previously determined Lon proteolytic domains from Escherichia coli, Methanococcus jannaschii, and Archaeoglobus fulgidus. There are six protomers in the asymmetric unit, four arranged as two dimers. The intersubunit interactions within the two dimers are similar to those between adjacent subunits of the hexameric ring of E. coli Lon, suggesting that the human Lon proteolytic domain also forms hexamers. The active site contains a 3 10 helix attached to the N-terminal end of a-helix 2, which leads to the insertion of Asp852 into the active site, as seen in M. jannaschii. Structural considerations make it likely that this conformation is proteolytically inactive. When comparing the intersubunit interactions of human with those of E. coli Lon taken with biochemical data leads us to propose a mechanism relating the formation of Lon oligomers with a conformational shift in the active site region coupled to a movement of a loop in the oligomer interface, converting the proteolytically inactive form seen here to the active one in the E. coli hexamer.

Mitochondrial Lon protease in human disease and aging: Including an etiologic classification of Lon-related diseases and disorders

“…The resolved structure of human mitochondrial Lon proteolytic domain is resembles those of the previously determined Lon proteolytic domains from Escherichia coli , with six protomers in the asymmetric unit. The active site contains a 3 10 helix attached to the N-terminal end of α-helix 2, which leads to the insertion of Asp852 into the active site [31]. The full –sequence human Lon protease is yet to be crystalized – but human Lon displays significant homology the bacterial protease La ( lon gene) and the yeast form of Lon, which is called Pim-1 ( PIM1 gene) [13,32].…”

Multitasking in the mitochondrion by the ATP-dependent Lon protease

“…Insights into the structure and function of mitochondrial Lon are provided by crystal structures of the bacterial holoenzymes from Bacillus subtilis and Thermococcus onnurineus NA1 ( Ton ) [21, 22], the truncated protease complex of E. coli Lon [40] as well as the isolated AAA + module, N and P domains [41–44]. The structure of the protease domain complex of E. coli Lon revealed a unique serine protease that employs a serine-lysine dyad at its active site [40].…”

Matrix proteases in mitochondrial DNA function

“…Lon protease forms a homo-oligomeric ring-shaped structure. As with bacterial Lon, human mitochondrial Lon protease likely forms a hexamer [4], whereas Saccharomyces cerevisiae ( S. cerevisiae ) mitochondrial Lon forms a heptamer [5]. In contrast, m -AAA comprises two subunits, paraplegin and an ATPase family gene 3-like 2 polypeptide (AFG3L2) and in humans, can form homo-hexameric structures of AFG3L2 only, or hetero-hexamers of AFG3L2 and paraplegin [6].…”