Understanding the Structure of Native Apolipoprotein-D Using an Integrative Structural Approach

Studying protein structure and dynamics provides valuable insights into a protein’s function and enables drug discovery. A multitude of techniques are available which provide deeper insights when used in an integrated fashion. This thesis studies the structure and dynamics of apolipoprotein-D (apoD), a small glycosylated lipocalin. ApoD transports small hydrophobic molecules in a β-barrel ligand binding pocket. Cerebral apoD is protective in Alzheimer’s disease through antioxidant function via a conserved methionine residue and attenuation of amyloid-β pathology. While the crystal structure of non-glycosylated apoD provided important insights, many questions regarding the structure of native, glycosylated apoD remained unanswered. The aims of this thesis were to determine the oligomeric state and structure of native apoD and determine how ligand binding influences apoD structure. This dissertation shows that native apoD in breast cyst fluid and cerebrospinal fluid forms oligomers, while in plasma, no apoD oligomers were found (Chapter 2). Two purification strategies for apoD from breast cyst fluid were devised. Purified native, glycosylated apoD was established as a stable tetramer of ~100 kDa using several orthogonal techniques. ApoD thereby joins the ranks of other oligomeric lipocalins while, methodologically, Chapter 2 underlines the importance of using multiple techniques to determine molecular weight of glycoproteins.