Molecule of the Month: Amyloid-beta Precursor Protein
Cell-clogging amyloids form when proteins improperly aggregate
Anatomy of APP
Bits and Pieces
APP is also broken into several functional fragments by a set of dedicated proteases, termed secretases. These proteases cut on either side of the small peptide shown here in green. The large piece on top is then released outside the cell, where it helps control nerve growth, and the small piece at the bottom is released inside the cell, where it interacts with the protein-synthesis machinery in the nucleus. The little peptide remaining in the middle is the portion that has received the most study, since it is a central player in Alzheimer's disease.
Exploring the Structure
Following its cleavage from APP, the amyloid-beta peptide can form fibrils that are associated with diseases such as Alzheimer’s. The structure on the right (PDB entry 1iyt) shows the peptide in an alpha-helical rich state, as it might look when interacting with the cell membrane. The structure on the left (PDB entry 2beg) shows how these peptides self-assemble into amyloid-beta fibrils. Each beta strand, or amyloid-beta monomer, interacts with neighboring strands to form parallel beta sheets. The beta sheet structure is stabilized through interactions of the abundance of hydrophobic residues (yellow) in amyloid-beta peptides. Additionally, inter-strand salt bridges connect the positively-charged lysine (blue) and the negatively-charged aspartic acid (pink). The bridges are formed through electrostatic attractions and hydrogen bonding between the side chains.
Select the JSmol tab to explore these structures in an interactive view.
This JSmol was designed and illustrated by Xinyi Christine Zhang.
July 2006, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2006_7