Copper and zinc ions govern the trans‐directed dimerization of APP family members in multiple ways

Abstract

The amyloid precursor protein (APP) and its homologs amyloid precursor‐like protein 1 (APLP1) and APLP2 have central physiological functions in transcellular adhesion that depend on copper and zinc mediated trans‐directed dimerization of the extracellular domains E1 and E2. Copper binds to three distinct sites in APP, one in the copper binding (CuBD) and growth factor‐like (GFLD) domains each within E1, and one in the E2 domain. For APLP1 and APLP2, metal binding has so far only been shown for the E2 domain. Zinc binding has been reported for all APP family members to a unique site in the E2 domain and an additional site essential for APLP1 E2 domain trans‐dimerization. Using isothermal titration calorimetry, co‐immunoprecipitation, and in vitro bead aggregation assays, we show that copper promotes cis‐ as well as trans‐directed dimerization of APLP1 and APLP2, similar as reported previously for APP. Furthermore, we report a APP‐specific zinc binding site with nanomolar affinity located in the E1 domain, whereas no binding of zinc to the individual subdomains GFLD or CuBD was detected. Zinc binding did not affect the cis‐ but trans‐dimerization of APP and APLP1. Furthermore, zinc binding inhibited copper‐induced trans‐directed dimerization of APP. Together, we identified a high‐affinity APP‐specific zinc binding site in the E1 domain and revealed contrasting cis‐ and trans‐directed dimerization properties of APP, APLP1, and APLP2 in dependence on zinc and copper ions. Consequently, changes in metal ion homeostasis, as reported in the context of synaptic activity and neurodegenerative diseases, appear as key modulators of homo‐ and heterotypic trans‐cellular APP/APLPs complexes.

Mitochondria and lipid peroxidation in the mechanism of neurodegeneration: Finding ways for prevention

“…In relation to the development of neurodegenerative diseases, transition metals are involved in the formation of cytotoxic protein aggregates from misfolded proteins as shown for PD, AD, HD, and ALS 67–72 . Moreover, transition metal accumulation and metal metabolism dysfunction have been shown for postmortem brain tissue of PD and AD patients 73–75 .…”

Zinc in Cognitive Impairment and Aging

“…Zinc can induce APP trans-dimerization at low concentrations; at low zinc concentrations, C186 and C187 in the E1 structural domain bind to zinc. They have a higher affinity for the appE1 structural domain than the E2 structural domain [ 56 ]. The formation of Aβ plaques and NFT after the formation of Aβ peptide aggregation by APP cleavage is the hallmark pathological change of AD.…”

„APP family member dimeric complexes are formed predominantly in synaptic compartments“

“…In contrast, APLP1 revealed a pattern of steady complex formation between 200 and 800 kDa, involving also dimerized complexes (Figure 1, 2) . The reason for the pattern of diverse high molecular weight complexes might be based on heparin or zinc induced APLP1 dimerization (August et al, 2019; Dahms et al, 2015; Dunsing et al, 2017; Mayer et al, 2014; Xue et al, 2011), differently glycosylated complexes (Paliga et al, 1997; Schilling et al, 2017), or processing by the transmembrane serine protease Matriptase, which cleaves APLP1 within the E1 domain and thereby negatively impacts APLP1 homodimerization (Lanchec et al, 2020).…”

“…Furthermore, copper induces dimer formation of APP in both, cis- and trans -orientation (August et al, 2019; Baumkotter et al, 2014) and also Cholesterol lowering drugs seem to promote APP dimerization (Langness et al, 2021). Another factor inducing APP dimerization is the glycosaminoglycan heparin (Dahms et al, 2010; Faham et al, 1996).…”