Phosphorylation-dependent metal binding by alpha-synuclein peptide fragments.

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Alpha-synuclein (alpha-syn) aggregation into Lewy bodies is central to Parkinson's disease pathogenesis.
• The C-terminal region of alpha-syn contains charged residues and phosphorylation sites, suggesting roles in metal ion interactions.
• Understanding these interactions is crucial for elucidating disease mechanisms.

Purpose of the Study:

• To investigate the metal-binding properties of specific C-terminal alpha-syn peptides and phosphopeptides.
• To determine how phosphorylation at different sites (tyrosine vs. serine) affects metal ion binding and peptide conformation.
• To explore the influence of various metal ions (e.g., Tb(3+), Fe(3+), Al(3+)) on alpha-syn peptide interactions.

Main Methods:

• Synthesis of model peptides and phosphopeptides representing alpha-syn residues 119-132.
• Utilized terbium(III) (Tb(3+)) luminescence as a probe for metal binding.
• Employed isothermal titration calorimetry (ITC) to quantify binding affinities.
• Applied electrospray ionization mass spectrometry (ESI-MS) to study interactions with other metal ions.
• Used circular dichroism (CD) spectroscopy to assess conformational changes.

Main Results:

• Phosphotyrosine at position 125 (pY125) exhibited marked selectivity for Tb(3+) compared to phosphoserine at 129 (pS129) or unphosphorylated peptide.
• The phosphoester group on tyrosine, along with nearby carboxylic acids, forms a multidentate ligand for metal ions.
• Fe(3+) and Al(3+) induced peptide dimerization via cross-linking and Fe(3+) induced partial folding of pY125.
• pY125 showed selectivity for trivalent over divalent metal ions.

Conclusions:

• The type and position of phosphorylation significantly impact alpha-syn peptide metal-binding specificity and affinity.
• Phosphotyrosine acts as a key metal-binding site, influencing peptide structure and potentially aggregation.
• These findings offer insights into the role of metal ions and post-translational modifications in alpha-synuclein's function and dysfunction in Parkinson's disease.