Dimerization of β-site β-amyloid precursor protein-cleaving enzyme

Gil G. Westmeyer, Michael Willem, Stefan F. Lichtenthaler, Glenn Lurman, Gerd Multhaup, Irmgard Assfalg-Machleidt, Karina Reiss, Paul Saftig, Christian Haass

Research output: Contribution to journalArticlepeer-review

105 Scopus citations

Abstract

Cleavage of the β-amyloid precursor protein (APP) by the aspartyl protease β-site APP-cleaving enzyme (BACE) is the first step in the generation of the amyloid β-peptide, which is deposited in the brain of Alzheimer's disease patients. Whereas the subsequent cleavage by γ-secretase was shown to originate from the cooperation of a multicomponent complex, it is currently unknown whether in a cellular environment BACE is enzymatically active as a monomer or in concert with other proteins. Using blue native gel electrophoresis we found that endogenous and overexpressed BACE has a molecular mass of 140 kDa instead of the expected mass of 70 kDa under denaturing conditions. This suggests that under native conditions BACE exists as a homodimer. Homodimerization was confirmed by co-immunoprecipitation of full-length BACE carrying different epitope tags. In contrast, the soluble active BACE ectodomain was exclusively present as a monomer both under native and denaturing conditions. A domain analysis revealed that the BACE ectodomain dimerized as long as it was attached to the membrane, whereas the cytoplasmic domain and the transmembrane domain were dispensable for dimerization. By adding a KKXX-endoplasmic reticulum retention signal to BACE, we demonstrate that dimerization of BACE occurs already before full maturation and pro-peptide cleavage. Furthermore, kinetic analysis of the purified native BACE dimer revealed a higher affinity and turnover rate in comparison to the monomeric soluble BACE. Dimerization of BACE might, thus, facilitate binding and cleavage of physiological substrates.

Original languageEnglish
Pages (from-to)53205-53212
Number of pages8
JournalJournal of Biological Chemistry
Volume279
Issue number51
DOIs
StatePublished - 17 Dec 2004
Externally publishedYes

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