The catalytic domain of insulin-degrading enzyme forms a denaturant-resistant complex with amyloid beta peptide: implications for Alzheimer disease pathogenesis

LLOVERA, R.E.; DE TULLIO, M.; ALONSO, L.G.; LEISSRING, M.A.; KAUFMAN, S.B.; ROHER, A.E.; PRAT GAY G. DE; MORELLI, L.; CASTAÑO, E.M.

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Año: 2008 vol. 283 p. 17039 - 17048

0021-9258

Insulin-degrading enzyme (IDE) is central to the turnover ofinsulin and degrades amyloid   (A ) in the mammalian brain.Biochemical and genetic data support the notion that IDE mayplay a role in late onset Alzheimer disease (AD), and recent studiessuggest an association between AD and diabetes mellitustype 2. Here we show that a natively folded recombinant IDE wascapable of forming a stable complex with A  that resisted dissociationafter treatment with strong denaturants. This interactionwas also observed with rat brain IDE and detected in anSDS-soluble fraction from AD cortical tissue. A  sequence17–27, known to be crucial in amyloid assembly, was sufficientto form a stable complex with IDE. Monomeric as opposed toaggregated A  was competent to associate irreversibly with IDEfollowing a very slow kinetics (t1⁄2   45 min). Partial denaturationof IDE as well as preincubation with a 10-fold molar excessof insulin prevented complex formation, suggesting that theirreversible interaction ofA  takes place with at least part of thesubstrate binding site of the protease. Limited proteolysisshowed thatA  remained bound to a 25-kDa N-terminal fragmentof IDE in an SDS-resistant manner. Mass spectrometryafter in gel digestion of the IDE A  complex showed that peptidesderived from the region that includes the catalytic site ofIDE were recovered with A . Taken together, these results aresuggestive of an unprecedented mechanism of conformationdependentsubstrate binding that may perturb A  clearance,insulin turnover, and promote AD pathogenesis.