title: Lysophospholipid-containing membranes modulate the fibril formation of the repeat domain of a human functional amyloid, pmel17.
abstract: Pmel17 is an important protein for pigmentation in human skin and eyes. Proteolytic fragments from Pmel17 form fibrils upon which melanin is deposited in melanosomes. The repeat domain (RPT) derived from Pmel17 only forms fibrils under acidic melanosomal conditions. Here, we examined the effects of lipids on RPT aggregation to explore whether intramelanosomal vesicles can facilitate fibrillogenesis. Using transmission electron microscopy, circular dichroism, and fluorescence spectroscopy, we monitored fibril formation at the ultrastructural, secondary conformational, and local levels, respectively. Phospholipid vesicles and lysophospholipid (lysolipid) micelles were employed as membrane mimics. The surfactant-like lysolipids are particularly pertinent due to their high content in melanosomal membranes. Interestingly, RPT aggregation kinetics were influenced only by lysolipid-containing phospholipid vesicles. While both vesicles containing either anionic lysophosphatidylglycerol (LPG) or zwitterionic lysophosphatidylcholine (LPC) stimulate aggregation, LPG exerted a greater effect on reducing the apparent nucleation time. A detailed comparison showed distinct behaviors of LPG versus LPC monomers and micelles plausibly originating from their headgroup hydrogen bonding capabilities. Acceleration and retardation of aggregation were observed for LPG monomers and micelles, respectively. Because a specific interaction between LPG and RPT was identified by intrinsic W423 fluorescence and induced α-helical structure, it is inferred that binding of LPG near the C-terminal amyloid core initiates intermolecular association, whereas stabilization of α-helical conformation inhibits β-sheet formation. Contrastingly, LPC promotes RPT aggregation at both submicellar and micellar concentrations via non-specific binding with undetectable secondary structural change. Our findings suggest that protein-lysolipid interactions within melanosomes may regulate amyloid formation in vivo.
authors.affiliation: Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-8013, USA.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Jiang
authors.affiliation: Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-8013, USA. Electronic address: leej4@mail.nih.gov.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008246:Lysophospholipids / Q000737:chemistry* / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D058951:gp100 Melanoma Antigen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D000682:Amyloid; D008246:Lysophospholipids; D008823:Micelles; C548637:PMEL protein, human; D058951:gp100 Melanoma Antigen
keywords: TEM; lysolipids; melanosome; protein–lipid interaction; tryptophan