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High‐order oligomers of intrinsically disordered brain proteins BASP1 and GAP‐43 preserve the structural disorder
Author(s) -
Forsova Oksana S.,
Zakharov Vladislav V.
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13692
Subject(s) - circular dichroism , chemistry , intrinsically disordered proteins , monomer , oligomer , biophysics , lipid raft , polyproline helix , crystallography , membrane , biochemistry , polymer , peptide , biology , organic chemistry
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 (PIP 2 ) 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 PIP 2 . We conclude that BASP1 and GAP‐43 oligomers preserve a mostly disordered structure, which may be of great importance for their function in PIP 2 signaling pathway.