Identification of a novel tetrameric structure for human apolipoprotein-D

Claudia S Kielkopf; Jason K K Low; Yee-Foong Mok; Surabhi Bhatia; Tony Palasovski; Aaron J Oakley; Andrew E Whitten; Brett Garner; Simon H J Brown

doi:10.1016/j.jsb.2018.05.012

Identification of a novel tetrameric structure for human apolipoprotein-D

J Struct Biol. 2018 Sep;203(3):205-218. doi: 10.1016/j.jsb.2018.05.012. Epub 2018 Jun 6.

Authors

Claudia S Kielkopf¹, Jason K K Low², Yee-Foong Mok³, Surabhi Bhatia⁴, Tony Palasovski⁵, Aaron J Oakley⁶, Andrew E Whitten⁷, Brett Garner⁸, Simon H J Brown⁹

Affiliations

¹ Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; School of Biological Sciences, University of Wollongong, Wollongong, NSW, Australia; Molecular Horizons, University of Wollongong, Wollongong, NSW, Australia. Electronic address: csk676@uowmail.edu.au.
² School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia. Electronic address: jason.low@sydney.edu.au.
³ Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia. Electronic address: ymok@unimelb.edu.au.
⁴ Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; School of Biological Sciences, University of Wollongong, Wollongong, NSW, Australia. Electronic address: surabhi.bhatia@sydney.edu.au.
⁵ Illawarra and Shoalhaven Local Health District (ISLHD), Wollongong, NSW, Australia; Specialist Breast Clinic Sutherland Shire and Wollongong, NSW, Australia; Integrated Specialist Health Care Sutherland Shire, NSW, Australia.
⁶ Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; Molecular Horizons, University of Wollongong, Wollongong, NSW, Australia; School of Chemistry, University of Wollongong, Wollongong, NSW, Australia. Electronic address: aarono@uow.edu.au.
⁷ Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia. Electronic address: awh@ansto.gov.au.
⁸ Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; School of Biological Sciences, University of Wollongong, Wollongong, NSW, Australia; Molecular Horizons, University of Wollongong, Wollongong, NSW, Australia. Electronic address: brettg@uow.edu.au.
⁹ Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; School of Biological Sciences, University of Wollongong, Wollongong, NSW, Australia; Molecular Horizons, University of Wollongong, Wollongong, NSW, Australia. Electronic address: simonb@uow.edu.au.

PMID: 29885491
DOI: 10.1016/j.jsb.2018.05.012

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.

Keywords: Apolipoprotein structure; Lipid; Lipocalin; Lipocalin structure; Oligomerization; Small-angle X-ray scattering (SAXS).

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Alzheimer Disease / genetics*
Alzheimer Disease / pathology
Amyloid beta-Peptides / chemistry
Animals
Apolipoproteins D / cerebrospinal fluid
Apolipoproteins D / chemistry*
Apolipoproteins D / genetics
Breast Cyst / chemistry
Crystallography, X-Ray
Disease Models, Animal
Humans
Ligands
Lipocalins / chemistry
Mice
Protein Binding
Protein Conformation*
Protein Multimerization*
Scattering, Small Angle

Substances

Amyloid beta-Peptides
Apolipoproteins D
Ligands
Lipocalins