A new brain metalloendopeptidase which degrades the Alzheimer ß-amyloid 1-40 peptide producing soluble fragments without neurotoxic effects

Abstract

A new metalloendopeptidase was purified to apparent homogeneity from a homogenate of normal human brain using successive steps of chromatography on DEAE-Trisacryl, hydroxylapatite and Sephacryl S-200. The purified enzyme cleaved the Gly 33 -Leu 34 bond of the 25-35 neurotoxic sequence of the Alzheimer ß-amyloid 1-40 peptide producing soluble fragments without neurotoxic effects. This enzyme activity was only inhibited by divalent cation chelators such as EDTA, EGTA and o-phenanthroline (1 mM) and was insensitive to phosphoramidon and captopril (1 µM concentration), specific inhibitors of neutral endopeptidase (EC 3.4.24.11) and angiotensin-converting enzyme (EC 3.4.15.1), respectively. The high affinity of this human brain endopeptidase for ß-amyloid 1-40 peptide (Km = 5 µM) suggests that it may play a physiological role in the degradation of this substance produced by normal cellular metabolism. It may also be hypothesized that the abnormal accumulation of the amyloid ß-protein in Alzheimer's disease may be initiated by a defect or an inactivation of this enzyme.

Proteolytic Degradation of Amyloid -Protein

“…Another important vasopeptidase implicated in the degradation of Ab is angiotensin-converting enzyme (ACE) (Carvalho et al 1997;Hu et al 2001). Because pharmaceutical ACE inhibitors are widely used to treat hypertension, the question of whether ACE is an endogenous regulator of Ab is a critical one.…”

β‐Amyloid Degradation and Alzheimer′s Disease

“…Many proteases or peptidases have been reported with the capability of cleaving Aβ either in vitro or in vivo. These include neprilysin (NEP) [ 14 – 16 ], endothelin-converting enzyme (ECE)-1 [ 17 ], insulin-degrading enzyme (IDE) [ 18 – 20 ], angiotensin-converting enzyme (ACE) [ 21 ], uPA/tPA-plasmin system [ 22 , 23 ], cathepsin D [ 24 , 25 ], gelatinase A [ 26 ], gelatinase B [ 27 ], matrix metalloendopeptidase-9 [ 28 ], coagulation factor XIa [ 29 ], antibody light chain c23.5 and hk14 [ 30 ], and α2-macroglobulin complexes [ 31 ]. Many of them have more than one cleavage site in the Aβ peptide ( Figure 3 ).…”

β-Amyloid: the key peptide in the pathogenesis of Alzheimer’s disease

“…The enzymes or proteases in proteolytic degradation play important roles by cleaving Aβ into shorter soluble fragments without neurotoxic effect. The proteases including cathepsin B (CatB), cathepsin D (CatD), Gelatinase A, serine protease factor Xia (FXIa), matrix metalloprotein-9 (MMP-9), neprilysin (NEP), presequence protease (Prep) and the α 2 M complex are involved in Aβ clearance ( Saporito-Irwin and Van Nostrand, 1995 ; Yamada et al, 1995 ; Hamazaki, 1996 ; Carvalho et al, 1997 ; Iwata et al, 2001 ; Mueller-Steiner et al, 2006 ; King et al, 2014 ), while enzymes such as angiotensin-converting enzyme (ACE), endothelin-converting enzyme (ECE), insulin-degrading enzyme (IDE), and uPT and tPA have been found to be involved in the degradation of Aβ ( Table 1B ; Ledesma et al, 2000 ; Tucker et al, 2002 ; Eckman et al, 2003 ; Farris et al, 2003 ; Hemming and Selkoe, 2005 ; Baranello et al, 2015 ).…”