Interfacial properties of the n-terminal lipid-binding domains of apolipoprotein B and their role in triacylglyceride-rich lipoprotein assembly
| Autor: | Mitsche, Matthew Alvin |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | Thesis/Dissertation |
| Popis: | Thesis (Ph.D.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. ApolipoproteinB (ApoB) is the principal protein component of triacylglyceride (TAG)-rich lipoproteins that are responsible for distribution of hydrophobic lipids to peripheral tissues and are the precursors to low density lipoprotein (LDL). TAG-rich lipoprotein assembly is initiated by the N-terminus of ApoB co-translationally binding and remodeling the luminal leaflet of the rough-ER. In this thesis, the adsorption and interfacial remodeling of the two N-terminal lipid-binding domains of ApoB (ApoB6-13 and 813-17) were characterized at a triolein/water (TO/W) and TO/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/W interface using drop tensiometry. A method was developed to form a monolayer of POPC at a TO/W interface and protocols were developed to characterize the exchangeability, surface pressure (Π)-area isotherm, and exclusion Π (ΠEX) at a TO/W or TO/POPC/W interface. A model for the behavior of amphipathic α-helices at a lipid/water interface was investigated by comparing the N- and C- termini of ApoA-1 ([1-44]ApoA-1 (N44) and [198-243]ApoA-I (C46)) using these protocols. Both helical peptides had a Π dependent surface conformation and had a higher affinity for a TO/POPC/W interface than a TO/W interface. The N-terminal lipid-binding domain of ApoB (ApoB6-13), the α-helical domain (aHD), has 17 α-helices with a heterogeneous amphipathic cross-section. The second lipid-binding domain, the C-Sheet (ApoB13-17), is 6 amphipathic β-strands. The adsorption, stress response, and viscoelasticity of the αHD and C-Sheet domains were generally consistent with the behavior of model amphipathic α-helices and β-strands, respectively. The αHD domain had a higher affinity for a TO/POPC/W interface than a TOIW interface, while the C-Sheet had a higher affinity for a TO/W interface. POPC shielded the C-Sheet from binding TO. The αHD adsorbed to a TO/W interface in a compact conformation where only the N-terminal eight helices interacted with the surface. When the protein monolayer was decompressed, the C-terminal helices bound the lipid. When adsorbed ApoB6-13 was compressed, theN-terminal four helices were progressively expelled from the surface. The remodeling occurred at five distinct transition points where the helices rearranged. There was no evidence of major remodeling of the C-Sheet during expansion and compression. This evidence was used to develop a more detailed model for the initiation of TAG-rich lipoprotein assembly. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|