Alpha-synuclein is the main component of the Lewy body of Parkinson’s disease. It contains 140 amino acids, and is ‘natively unfolded’ in that it has no apparent ordered secondary structure (alpha helices, beta pleated sheets) detectable by a variety of methods — far ultraviolet circular dichroism, Fourier transform infrared spectroscopy or NMR spectroscopy. When the protein binds to artificial membranes half of it forms alpha helices. Amazingly, after a huge amount of work we don’t know what alpha-Synuclein actually does. Knockouts have only minor CNS abnormalities.
However, alpha synuclein forms fibrils which bind to cell surface receptors with internalization and transmission to other cells, just like prions. Two such receptors for alpha-synuclein fibrils are Lymphocyte Activation Gene E (LAG3) and Amyloid PrecursorLike Protein 1 (ALPL1).
LAG3 has 4 immunoglobulin like domains (D1 – D4). It uses D1 to capture the carboxy terminus which is exposed and concentrated on the surface of the alpha-synuclein fibrils.
Interestingly the monomers are said to adopt a self-shielded conformation which impedes the exposure of the carboxy terminus. Phosphorylation of serine #129 enhances the binding of alpha-synuclein preformed fibrils to LAG3 and APLP1. So the carboxy terminus of alpha-synuclein is a promising traget to block Parkinson’s disease progression.
