The following proteins belongs to a family of proteases which are dependent on
the hydrolysis of ATP for their activity and which have a serine in their
Bacterial ATP-dependent proteases [1,2]. The prototype of those bacterial
enzymes is the Escherichia coli La protease (EC 188.8.131.52) (gene lon). La
is capable of hydrolyzing large proteins; it degrades short-lived
regulatory (such as rcsA and sulA) and abnormal proteins. It is a
cytoplasmic protein of 87 Kd that associates as an homotetramer. Its
proteolytic activity is stimulated by single-stranded DNA.
Eukaryotic mitochondrial matrix proteases [3,4]. The prototype of these
enzymes is the yeast PIM1 protease. It is a mitochondrial matrix protein of
120 Kd that associated as an homohexamer. It catalyzes the initial step of
mitochondrial protein degradation.
Haemophilus influenzae lon-B (HI1324), a protein which does not contain the
ATP-binding domain, but possess a slightly divergent form of the catalytic
The region around the serine residue involved in the catalytic mechanism 
is perfectly conserved and can be used as a signature pattern.
Proteins belonging to this family also contain a copy of the ATP/GTP-
binding motif 'A' (P-loop) (see <PDOC00017>).
These proteins belong to family S16 in the classification of peptidases
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