alpha-Synuclein exhibits competitive interaction between calmodulin and synthetic membranes.
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.
D000818:Animals; D001667:Binding, Competitive / Q000502:physiology*; D001923:Brain Chemistry; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008567:Membranes, Artificial; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017386:Sequence Homology, Amino Acid; D051843:Synucleins; D051844:alpha-Synuclein; D051846:beta-Synuclein
D002147:Calmodulin; D003432:Cross-Linking Reagents; D008081:Liposomes; D008567:Membranes, Artificial; D009419:Nerve Tissue Proteins; C497606:Snca protein, rat; C497609:Sncb protein, rat; D051843:Synucleins; D051844:alpha-Synuclein; D051846:beta-Synuclein