The formation of a stable complex between Ab and insulin-degrading enzyme : a possible trans-acting pathway of amyloid self-propagation in the brain

LLOVERA RE; ALONSO LG; FERNADEZ GAMBA A; DI TULLIO M; DE PRAT GAY G; MORELLI L; CASTAÑO EM

Pinamar (Argentina)

Congreso; XLI annual meeting (SAIB) and Protein Symposium; 2005

SAIB

The accumulation of aggregated amyloid b of 40-42 residues in the  brain is a major pathogenic mechanism in several neurodegenerative  diseases. Insulin degrading enzyme (IDE) is a zinc-  metalloendopeptidase that removes brain soluble Ab under physiologic conditions. In the course of our study of Ab-IDE  interaction, we found that upon incubation in vitro, in presence or  absence of specific inhibitor for IDE, Ab was capable of forming a  complex with the enzyme that resisted boiling in 4% SDS-0.1M DTT. Moreover, this component was not dissociated in 8 M urea  or 70% formic acid, underscoring its high stability. We further  mapped the interaction to the region 16-28 of Ab, by using an N-terminal fluorescein-labeled Ab16-28. We found that complex formation was a very slow process (t1/2~ 45 min) and it was  specifically out competed with insulin, another substrate of IDE.  These findings suggest that although the formation of stable Ab-IDE complexes may not be dependent on the catalytic mechanism,  it requires the interaction of the central region of Aâ with the substrate binding site of IDE, or at least a part of it. The full  characterization of a non-productive pathway in Ab-IDE interaction  and its detection in vivo may provide novel insights about the self-propagation of the amyloidogenic process in the brain. (Alzheimer´s Association IIRG035312, PICT2002-10599).