alpha-Synuclein exhibits competitive interaction between calmodulin and synthetic membranes

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Alpha-synuclein is a key component of Lewy bodies in Parkinson's disease.
• It is implicated in membrane biogenesis through amphipathic alpha-helix induction.
• Amphipathic alpha-helices are recognized by calmodulin, suggesting a potential interaction.

Purpose of the Study:

• To investigate the molecular interaction between alpha-synuclein and calmodulin.
• To determine the role of calcium in this interaction.
• To elucidate the functional consequences of alpha-synuclein-calmodulin binding.

Main Methods:

• Chemical coupling reagent (N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline) for complex formation.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
• Aggregation kinetics assays.
• Reversible binding assays with varying calcium concentrations.
• Use of C-terminally truncated alpha-synuclein (alpha-syn97).
• Liposome and immobilized calmodulin competition assays.

Main Results:

• Alpha-synuclein forms a 1:1 complex with calmodulin in the presence and absence of calcium.
• Beta-synuclein's interaction with calmodulin is more calcium-dependent.
• Calmodulin selectively affects alpha-synuclein aggregation, independent of calcium.
• Alpha-synuclein binds Ca2+-free and Ca2+-bound calmodulin with similar affinities (Kd ≈ 0.3 µM).
• The N-terminal region of alpha-synuclein mediates calmodulin binding.
• Alpha-synuclein competes with membranes for calmodulin binding, releasing bound alpha-synuclein.

Conclusions:

• Alpha-synuclein acts as a negative regulator of calmodulin, irrespective of calcium presence.
• The interaction occurs at the interface between calmodulin and membranes.
• This suggests a novel regulatory mechanism involving alpha-synuclein, calmodulin, and membrane interactions in cellular processes.