title: High-order oligomers of intrinsically disordered brain proteins BASP1 and GAP-43 preserve the structural disorder.
abstract: Brain acid-soluble protein-1 (BASP1) and growth-associated protein-43 (GAP-43) are presynaptic membrane proteins participating in axon guidance, neuroregeneration and synaptic plasticity. They are presumed to sequester phosphatidylinositol-4,5-bisphosphate (PIP2 ) in lipid rafts. Previously we have shown that the proteins form heterogeneously sized oligomers in the presence of anionic phospholipids or SDS at submicellar concentration. BASP1 and GAP-43 are intrinsically disordered proteins (IDPs). In light of this, we investigated the structure of their oligomers. Using partial cross-linking of the oligomers with glutaraldehyde, the aggregation numbers of BASP1 and GAP-43 were estimated as 10-14 and 6-7 monomer subunits, respectively. The cross-linking pattern indicated that the subunits are circularly arranged. The circular dichroism (CD) spectra of the monomers were characteristic of coil-like IDPs showing unordered structure with a high population of polyproline-II conformation. The oligomerization was accompanied by a minor CD spectral change attributable to formation of a small amount of α-helix. The number of residues in the α-helical conformation was estimated as 13 in BASP1 and 18 in GAP-43. However, the overall structure of the oligomers remained disordered, indicating a high degree of 'fuzziness'. This was confirmed by measuring the hydrodynamic dimensions of the oligomers using polyacrylamide gradient gel electrophoresis and size-exclusion chromatography, and by assaying their sensitivity to proteolytic digestion. There is evidence that the observed α-helical folding occurs within the basic effector domains, which are presumably tethered together via anionic molecules of SDS or PIP2 . We conclude that BASP1 and GAP-43 oligomers preserve a mostly disordered structure, which may be of great importance for their function in PIP2 signaling pathway.
authors.affiliation: Molecular and Radiation Biophysics Division, B. P. Konstantinov Petersburg Nuclear Physics Institute, National Research Centre 'Kurchatov Institute', Gatchina, Russia.|Laboratory of Natural Polymers, Institute of Macromolecular Compounds, Russian Academy of Sciences, St Petersburg, Russia.
authors.forename: Oksana S
authors.initials: OS
authors.lastname: Forsova
authors.affiliation: Molecular and Radiation Biophysics Division, B. P. Konstantinov Petersburg Nuclear Physics Institute, National Research Centre 'Kurchatov Institute', Gatchina, Russia.|Laboratory of Natural Polymers, Institute of Macromolecular Compounds, Russian Academy of Sciences, St Petersburg, Russia.|Department of Biophysics, Institute of Physics, Nanotechnology and Telecommunications, Peter the Great St Petersburg Polytechnic University, Russia.
authors.forename: Vladislav V
authors.initials: VV
authors.lastname: Zakharov
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002942:Circular Dichroism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D019922:GAP-43 Protein / Q000737:chemistry* / Q000378:metabolism; D064267:Intrinsically Disordered Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D003432:Cross-Linking Reagents; D019922:GAP-43 Protein; D064267:Intrinsically Disordered Proteins; D009419:Nerve Tissue Proteins
keywords: brain proteins BASP1 and GAP-43; circular dichroism; fuzzy complexes; intrinsically disordered proteins; protein oligomers