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MOLECULAR STRUCTURE OF AN APOLIPOPROTEIN DETERMINED AT 2.5-ANGSTROMS RESOLUTIONMOLECULAR STRUCTURE OF AN APOLIPOPROTEIN DETERMINED AT 2.5-ANGSTROMS RESOLUTION
Structural highlights
FunctionAPL3_LOCMI Assists in the loading of diacylglycerol, generated from triacylglycerol stores in the fat body through the action of adipokinetic hormone, into lipophorin, the hemolymph lipoprotein. It increases the lipid carrying capacity of lipophorin by covering the expanding hydrophobic surface resulting from diacylglycerol uptake. It thus plays a critical role in the transport of lipids during flight in several species of insects. Publication Abstract from PubMedThe three-dimensional structure of an apolipoprotein isolated from the African migratory locust Locusta migratoria has been determined by X-ray analysis to a resolution of 2.5 A. The overall molecular architecture of this protein consists of five long alpha-helices connected by short loops. As predicted from amino acid sequence analyses, these helices are distinctly amphiphilic with the hydrophobic residues pointing in toward the interior of the protein and the hydrophilic side chains facing outward. The molecule falls into the general category of up-and-down alpha-helical bundles as previously observed, for example, in cytochrome c'. Although the structure shows the presence of five long amphiphilic alpha-helices, the alpha-helical moment and hydrophobicity of the entire molecule fall into the range found for normal globular proteins. Thus, in order for the amphiphilic helices to play a role in the binding of the protein to a lipid surface, there must be a structural reorganization of the protein which exposes the hydrophobic interior to the lipid surface. The three-dimensional motif of this apolipoprotein is compatible with a model in which the molecule binds to the lipid surface via a relatively nonpolar end and then spreads on the surface in such a way as to cause the hydrophobic side chains of the helices to come in contact with the lipid surface, the charged and polar residues to remain in contact with water, and the overall helical motif of the protein to be maintained. Molecular structure of an apolipoprotein determined at 2.5-A resolution.,Breiter DR, Kanost MR, Benning MM, Wesenberg G, Law JH, Wells MA, Rayment I, Holden HM Biochemistry. 1991 Jan 22;30(3):603-8. PMID:1988048[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References |
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