| A 17-aa peptide sequence, mapping nears the cytoplasmic N-terminus of rat DINE. The amyloid beta-peptide (Ab) of 39 to 43aa (Ab40, Ab42, Ab43) is constitutively produced in brain upon proteolysis of the b-amyloid precursor protein (APP). In the young and healthy humans, Ab is rapidly catabolized before it can be deposited in the brain. However, upon aging or the onset of familial Alzheimers Disease, alterations in either synthesis or degradation/clearance of Ab may contribute to amyloid depositions in the brain. Ab is susceptible to a number of in vivo and in vitro proteases like cathepsin-D and M-13 metalloproteases. The M-13 family includes several members of zinc-dependent proteases like damage-induced neuronal endopeptidase (DINE), product of phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX), neutral endopeptidase 24.11 or neprilysin (NEP) and neprilysin-like proteases (NEPLs). NEPLs (alpha, -beta, gamma) arise from the alternative splicing of a single NELPS gene and show ~54% sequence homology. M13 members are generally type II transmembrane proteins consisting of a single polypeptide chain with Zinc binding HEXXH motif, a short cytoplasmic tail, a transmembrane segment and an extra-cytoplasmic domain containing the enzyme active site. DINE (damage-induced neuronal endopeptidase) or Endothelin converting enzyme-like 1 (ECEL1) or X-converting enzyme (Xce) is a 95kD (mouse/rat/human 775 aa, chromosome 2q36-q37), type II integral membrane metalloprotease containing a conserved zinc-binding motif and an ENXADX consensus sequence, consistent with gluzinitin. The aa sequence of DINE is 36 and 32 % identical to ECE-1 and NEP, respectively. But, DINE is devoid of enzyme activity like ECE. Unlike NEP, DINE has no proteolytic activity to Ab. However, the enzyme can hydrolyze synthetic NEP substrates and thiorphan, EDTA and phosphoramidon inhibit its activity. DINE also inhibits C2-ceramide induced apoptosis in COS-7 cells. Although, the endogenous substrate for DINE is yet to be identified, its proteolytic activity activates, at least in part, free radical scavenging in damaged neurons. The DINE expression is restricted to brain tissue with predominant expression in hypothalamus, large cholinergic cells in striatum and low expression in virtually all regions of brain except in cerebral cortex, hippocampus and cerebellum. DINE, expression is markedly increased in response to optic, spinal sensory, cortical and thalamic nerve injury. |
