Transient Structure of the Amyloid Precursor Protein Cytoplasmic Tail Indicates Preordering of Structure for Binding to Cytosolic Factors^†

The cytoplasmic tail of the amyloid precursor protein (APP) appears to play two important roles in the cell through participation in intracellular signaling and proteolytic processing of APP. Hence, knowledge of the structure of the 47 residue cytoplasmic tail of APP is important for understanding the molecular interactions involved in normal cell function as well as in the pathogenesis of Alzheimer's disease. Multidimensional solution NMR spectroscopy has been applied to examine the structural features of a 49-residue peptide (APP-C) containing two N-terminal residues (GS) and the APP cytoplasmic tail, over the pH range of 4.2−7.1. Although the peptide does not adopt a stable folded structure, regions of unstable structure exist over the pH range examined and have been characterized by a combination of H^α chemical shifts, NOE analysis, and ³J_HNHα coupling constants and by identification of transient hydrogen bonds between amide protons and titrating carboxylate groups. These studies extend the work of others [Kroenke et al. (1997) Biochemistry 36, 8145−8152] by identifying an additional nascent helix and a hydrophobic cluster within the N-terminal 20 amino acid residues and by further characterizing the TPEE turn as a helix capping box. The transient structure of APP-C provides insight into the importance of preordering of this cytoplasmic tail in governing specificity and affinity for cytosolic binding partners.