#Elucidate ai series#

These conformational changes alter the abilities of apoA-I and apoE to function as ligands for their receptors. The latter domain initiates lipid binding and this interaction induces changes in conformation the alpha-helix content increases and the amino-terminal helix bundle can open subsequently. The helices located in the amino-terminal two-thirds of the molecule adopt a helix bundle structure while the carboxy-terminal segment forms a separately folded, relatively disorganized, domain.

#Elucidate ai series#

ApoA-I and apoE, which are the best characterized in structural terms, contain a series of amphipathic alpha-helical repeats. The structures and cholesterol transport abilities of HDL particles are determined by the properties of their exchangeable apolipoprotein (apo) components. High density lipoprotein (HDL) possesses important anti-atherogenic properties and this review addresses the molecular mechanisms underlying these functions. In this chapter, we describe strategies for the preparation of rHDL particles containing GPCRs in their monomeric form and discuss various methodologies used to analyze the reconstituted receptor function. Our laboratory and others have utilized the rHDL approach to study the behavior of G protein-coupled receptors. Investigators have utilized this model bilayer system to co-reconstitute membrane proteins, and take advantage of the small size and its monodispersion. Reconstituted HDL particles can be assembled in vitro using purified apoA-1 and purified lipids.

These monodispersed, nanoscale discoidal HDL particles are approximately 10-11 nm in diameter with a thickness that is dependent on the length of the phospholipid acyl chain. The amphipathic nature of apoA-1 shields the hydrophobic acyl chains of the lipids from solvent and keeps the particles soluble in aqueous environments. They consist of a discoidal-shaped planar bilayer of phospholipids that is surrounded by a dimer of apolipoprotein A-I (apoA-I). Reconstituted high-density lipoprotein particles (rHDL) are powerful platforms used as a model phospholipid bilayer system to study membrane proteins. Further insights into the lipid-bound conformation of apolipoproteins are required to fully understand their functional role under physiological conditions. This review compares the apolipoprotein high-resolution structures and the factors that trigger this switch in insect apolipophorin III and the mammalian apolipoproteins, apolipoprotein E and apolipoprotein A-I, pointing out the commonalities and key differences in the mode of lipid interaction. A conformational switch then permits helix-helix interactions to be substituted by helix-lipid interactions upon lipid binding interaction.

Composed of a series of four or five amphipathic alpha-helices that fold to form a helix bundle, this motif allows the en face orientation of the hydrophobic faces of the alpha-helices in the protein interior in the lipid-free state. This approach has provided refined structural information on apolipoprotein A-I folding which had eluded all previous approaches.ДЄpolipoproteins are the protein components of lipoproteins that have the innate ability to inter convert between a lipid-free and a lipid-bound form in a facile manner, a remarkable property conferred by the helix bundle motif.

Recent advances in mass spectrometric sequencing of cross-linked peptides provide an excellent tool to help define protein tertiary structure. Investigations are all aimed at defining the conformation of lipid-bound apolipoprotein A-I which may provide an explanation for how specific domains of apolipoprotein A-I interact with important HDL-modifying proteins that ultimately determine the apolipoprotein's fate in circulation. Recent studies have focused on determining the exact helix-helix registry and salt-bridging partners found on a two apolipoprotein A-I molecule disc as well as on spherical HDL particles. Since the X-ray crystal structure of lipid-free Delta43 apolipoprotein A-I was reported in 1997, a 'double belt' model describing lipid-bound apolipoprotein A-I conformation for recombinant HDL has prevailed. Given the current interest in understanding the structure of HDL apolipoprotein A-I, this approach seems ideal in assessing its dual role as mediator of lipid efflux and modulator of cellular inflammation.ДЄ large number of different technical approaches have been employed over the past 25 years in attempts to solve the lipid-bound conformation of apolipoprotein A-I. The purpose of this review is to highlight recent advances in mass spectrometry and its use for identifying the lipid-bound conformation of apolipoprotein A-I.