alpha-Synuclein Exhibits Competitive Interaction Between Calmodulin and Synthetic Membranes

J Neurochem. 2002 Sep;82(5):1007-17. doi: 10.1046/j.1471-4159.2002.01024.x.

Abstract

alpha-Synuclein, a pathological component of Parkinson's disease by constituting the Lewy bodies, has been suggested to be involved in membrane biogenesis via induction of amphipathic alpha-helices. Since the amphipathic alpha-helix is also known as a recognition signal of calmodulin for its target proteins, molecular interaction between alpha-synuclein and calmodulin has been investigated. By employing a chemical coupling reagent of N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline, alpha-synuclein has been shown to yield a heterodimeric 1 : 1 complex with calmodulin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and even absence of calcium, whereas beta-synuclein was more dependent upon calcium for its calmodulin interaction. The selective calmodulin interaction of alpha-synuclein in the absence of calcium was also demonstrated with the aggregation kinetics of the synucleins in which only the alpha-synuclein aggregation was affected by calmodulin. A reversible binding assay confirmed that alpha-synuclein interacted with the Ca2+-free as well as the Ca2+-bound calmodulins with almost identical Kds of 0.35 micro m and 0.31 micro m, respectively, while beta-synuclein preferentially recognized the Ca2+-bound form with a Kd of 0.68 micro m. By using a C-terminally truncated alpha-synuclein of alpha-syn97, the calmodulin binding site(s) on alpha-synuclein was(were) shown to be located on the N-terminal region where the amphipathic alpha-helices have been suggested to be induced upon membrane interaction. By employing liposome and calmodulin in a state of being either soluble or immobilized on agarose, actual competition of alpha-synuclein between membranes and calmodulin was demonstrated with the observation that alpha-synuclein previously bound to the liposome was released upon specific interaction with the calmodulins. Taken together, these data may suggest that alpha-synuclein could act not only as a negative regulator for calmodulin in the presence and even absence of calcium, but it could also exert its activity at the interface between calmodulin and membranes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding, Competitive / physiology*
  • Brain Chemistry
  • Calmodulin / chemistry*
  • Calmodulin / metabolism
  • Cross-Linking Reagents / chemistry
  • Liposomes / chemistry
  • Membranes, Artificial*
  • Molecular Sequence Data
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / metabolism
  • Protein Binding / physiology
  • Rats
  • Sequence Homology, Amino Acid
  • Synucleins
  • alpha-Synuclein
  • beta-Synuclein

Substances

  • Calmodulin
  • Cross-Linking Reagents
  • Liposomes
  • Membranes, Artificial
  • Nerve Tissue Proteins
  • Snca protein, rat
  • Sncb protein, rat
  • Synucleins
  • alpha-Synuclein
  • beta-Synuclein