title: Calcium-triggered membrane interaction of the alpha-synuclein acidic tail.
abstract: Alpha-synuclein (alpha-syn) is a 140-residue protein that aggregates in intraneuronal inclusions called Lewy bodies in Parkinson's disease (PD). It is composed of an N-terminal domain with a propensity to bind lipids and a C-terminal domain rich in acidic residues (the acidic tail). The objective of this study was to examine the effect of Ca(2+) on the acidic tail conformation in lipid-bound alpha-syn. We exploit the extreme sensitivity of the band III fluorescence emission peak of the pyrene fluorophore to the polarity of its microenvironment to monitor subtle conformational response of the alpha-syn acidic tail to Ca(2+). Using recombinant human alpha-syn bearing a pyrene to probe either the N-terminal domain or the acidic tail, we noted that lipid binding resulted in an increase in band III emission intensity in the pyrene probe tagging the N-terminal domain but not that in the acidic tail. This suggests that the protein is anchored to the lipid surface via the N-terminal domain. However, addition of Ca(2+) caused an increase in band III emission intensity in the pyrene tagging the acidic tail, with a corresponding increased susceptibility to quenching by quenchers located in the lipid milieu, indicative of lipid interaction of this domain. Taken together with the increased beta-sheet content of membrane-associated alpha-syn in the presence of Ca(2+), we propose a model wherein initial lipid interaction occurs via the N-terminal domain, followed by a Ca(2+)-triggered membrane association of the acidic tail as a potential mechanism leading to alpha-syn aggregation. These observations have direct implications in the role of age-related oxidative stress and the attendant cellular Ca(2+) dysregulation as critical factors in alpha-syn aggregation in PD.
authors.affiliation: Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, California 94609, USA.
authors.forename: Shiori
authors.initials: S
authors.lastname: Tamamizu-Kato
authors.forename: Malathi G
authors.initials: MG
authors.lastname: Kosaraju
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kato
authors.forename: Vincent
authors.initials: V
authors.lastname: Raussens
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Ruysschaert
authors.forename: Vasanthy
authors.initials: V
authors.lastname: Narayanaswami
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002942:Circular Dichroism; D005453:Fluorescence; D020404:Glycerophospholipids / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry; D011487:Protein Conformation; D011721:Pyrenes / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051844:alpha-Synuclein / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C509561:1-palmitoyl-2-oleoyl-phosphatidyl-3-adenosine; D020404:Glycerophospholipids; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D011721:Pyrenes; D011994:Recombinant Proteins; D051844:alpha-Synuclein; D000241:Adenosine; D002118:Calcium; C028694:1-palmitoyl-2-oleoylphosphatidylcholine