Lon (also known as endopeptidase La, EC 3.4.21.53) is a multi-domain ATP-dependent protease found throughout all kingdoms of life. It is involved in protein quality control and several regulatory processes. All Lon proteases contain an ATPase domain belonging to the AAA+ superfamily of molecular machines, and a proteolytic domain with a serine-lysine catalytic dyad in which a lysine assists the catalytic serine in proteolytic cleavage. Lon proteases can be divided into two subfamilies: A type (A-Lons), which have a large multi-lobed N-terminal domain (see <PDOC51787>) together with the ATPase and protease domains, and B type (B-Lons), which lack an N domain, but have a membrane-anchoring region emerging from the ATPase domain. B-Lons are found in Archaea, in which they are the lone membrane-anchored ATP-dependent protease. The soluble A-Lons are found in all bacteria and in eukaryotic cell organelles, such as mitochondria and peroxisomes, and are needed for recovery from various stress conditions [1,2,3,4,5,6]. The Lon proteolytic domain forms peptidase family S16 of clan SJ [3,E1].

The structure of the Lon proteolytic domain consists of six α helices and ten β strands (see <PDB:1RR9>) [1,2,3,4,5].

The profile we developed covers the entire Lon proteolytic domain.