Structural, physiological and pathogenic features of APP/APLPs E1 domain

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Deletion of the APP family members leads to a decreased neurotransmission at the neuromuscular junction, possibly caused by a loss of fianction of APP family proteins in neuronal cell adhesion. We assume that APP/APLPs dependent cell adhesion is mediated by direct trans- interaction of the E1 domain of APP/APLPs. To test this hypothesis, we intend to purify the El domain and the complete extracellular domain of APP/APLPs, using His-tagged mutant constructs. The purified proteins will be subjected to crystallization and X-ray structural analysis as well as biophysical characterizafion like Isothermal Titration Calorimetry and Static Light Scattering to determine their dimerization properties. Secondly, we will use an in vitro trans-dimerization assay to purify and determine modulators of homotypic APLPl and APLP2 trans-interaction. Similarly, we will screen for modulators of APP/APLPs heterotypic trans-dimerization. The novel putative APP/APLPs trans-dimerization modifiers will be tested in cell based clustering assays and primary neuronal cultures. Thirdly, we will determine the subcellular localization of APP/APLPs at the synapse and at extra-synapfic sites at the plasma membrane, using high-resolution light microscopy. Finally, we will investigate if the extracellular domain of APP/APLPs is sufficient to induce post- or presynaptic differentiation and will determine the sequence of underlying molecular and cellular events by life cell imaging. All together these analyses will help to understand the function of homo- and heterotypic trans-interaction of the APP gene family at the synapse.