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Identification of a novel tetrameric structure for human apolipoprotein-D

Journal Article


Abstract


  • Apolipoprotein-D is a 25 kDa glycosylated member of the lipocalin family that folds into an eight-stranded β-barrel with a single adjacent α-helix. Apolipoprotein-D specifically binds a range of small hydrophobic ligands such as progesterone and arachidonic acid and has an antioxidant function that is in part due to the reduction of peroxidised lipids by methionine-93. Therefore, apolipoprotein-D plays multiple roles throughout the body and is protective in Alzheimer's disease, where apolipoprotein-D overexpression reduces the amyloid-β burden in Alzheimer's disease mouse models. Oligomerisation is a common feature of lipocalins that can influence ligand binding. The native structure of apolipoprotein-D, however, has not been conclusively defined. Apolipoprotein-D is generally described as a monomeric protein, although it dimerises when reducing peroxidised lipids. Here, we investigated the native structure of apolipoprotein-D derived from plasma, breast cyst fluid (BCF) and cerebrospinal fluid. In plasma and cerebrospinal fluid, apolipoprotein-D was present in high-molecular weight complexes, potentially in association with lipoproteins. In contrast, apolipoprotein-D in BCF formed distinct oligomeric species. We assessed apolipoprotein-D oligomerisation using native apolipoprotein-D purified from BCF and a suite of complementary methods, including multi-angle laser light scattering, analytical ultracentrifugation and small-angle X-ray scattering. Our analyses showed that apolipoprotein-D predominantly forms a ∼95 to ∼100 kDa tetramer. Small-angle X-ray scattering analysis confirmed these findings and provided a structural model for apolipoprotein-D tetramer. These data indicate apolipoprotein-D rarely exists as a free monomer under physiological conditions and provide insights into novel native structures of apolipoprotein-D and into oligomerisation behaviour in the lipocalin family.

Authors


  •   Kielkopf, Claudia (external author)
  •   Low, Jason (external author)
  •   Mok, Yee-Foong (external author)
  •   Bhatia, Surabhi (external author)
  •   Palasovski, Tony (external author)
  •   Oakley, Aaron J.
  •   Whitten, Andrew (external author)
  •   Garner, Brett
  •   Brown, Simon H. J.

Publication Date


  • 2018

Citation


  • Kielkopf, C. S., Low, J. K. K., Mok, Y., Bhatia, S., Palasovski, T., Oakley, A. J., Whitten, A. E., Garner, B. & Brown, S. H. J. (2018). Identification of a novel tetrameric structure for human apolipoprotein-D. Journal of Structural Biology, 203 205-218.

Scopus Eid


  • 2-s2.0-85048780856

Number Of Pages


  • 13

Start Page


  • 205

End Page


  • 218

Volume


  • 203

Place Of Publication


  • United States

Abstract


  • Apolipoprotein-D is a 25 kDa glycosylated member of the lipocalin family that folds into an eight-stranded β-barrel with a single adjacent α-helix. Apolipoprotein-D specifically binds a range of small hydrophobic ligands such as progesterone and arachidonic acid and has an antioxidant function that is in part due to the reduction of peroxidised lipids by methionine-93. Therefore, apolipoprotein-D plays multiple roles throughout the body and is protective in Alzheimer's disease, where apolipoprotein-D overexpression reduces the amyloid-β burden in Alzheimer's disease mouse models. Oligomerisation is a common feature of lipocalins that can influence ligand binding. The native structure of apolipoprotein-D, however, has not been conclusively defined. Apolipoprotein-D is generally described as a monomeric protein, although it dimerises when reducing peroxidised lipids. Here, we investigated the native structure of apolipoprotein-D derived from plasma, breast cyst fluid (BCF) and cerebrospinal fluid. In plasma and cerebrospinal fluid, apolipoprotein-D was present in high-molecular weight complexes, potentially in association with lipoproteins. In contrast, apolipoprotein-D in BCF formed distinct oligomeric species. We assessed apolipoprotein-D oligomerisation using native apolipoprotein-D purified from BCF and a suite of complementary methods, including multi-angle laser light scattering, analytical ultracentrifugation and small-angle X-ray scattering. Our analyses showed that apolipoprotein-D predominantly forms a ∼95 to ∼100 kDa tetramer. Small-angle X-ray scattering analysis confirmed these findings and provided a structural model for apolipoprotein-D tetramer. These data indicate apolipoprotein-D rarely exists as a free monomer under physiological conditions and provide insights into novel native structures of apolipoprotein-D and into oligomerisation behaviour in the lipocalin family.

Authors


  •   Kielkopf, Claudia (external author)
  •   Low, Jason (external author)
  •   Mok, Yee-Foong (external author)
  •   Bhatia, Surabhi (external author)
  •   Palasovski, Tony (external author)
  •   Oakley, Aaron J.
  •   Whitten, Andrew (external author)
  •   Garner, Brett
  •   Brown, Simon H. J.

Publication Date


  • 2018

Citation


  • Kielkopf, C. S., Low, J. K. K., Mok, Y., Bhatia, S., Palasovski, T., Oakley, A. J., Whitten, A. E., Garner, B. & Brown, S. H. J. (2018). Identification of a novel tetrameric structure for human apolipoprotein-D. Journal of Structural Biology, 203 205-218.

Scopus Eid


  • 2-s2.0-85048780856

Number Of Pages


  • 13

Start Page


  • 205

End Page


  • 218

Volume


  • 203

Place Of Publication


  • United States