Apolipophorin III: a lipid-triggered molecular switch.
Apolipophorin III (apoLp-III) is a low molecular weight exchangeable apolipoprotein that plays an important role in the enhanced neutral lipid transport during insect flight. The protein exists in lipid-free and lipid-bound states. The lipid-bound state is the active form of the protein and occurs when apoLp-III associates with lipid-enriched lipophorins. ApoLp-III is well characterized in two evolutionally divergent species: Locusta migratoria and Manduca sexta. The two apolipoproteins interact in a similar manner with model phospholipid vesicles, and transform them into discoidal particles. Their low intrinsic stability in the lipid-free state likely facilitates interaction with lipid surfaces. Low solution pH also favors lipid binding interaction through increased exposure of hydrophobic surfaces on apoLp-III. While secondary structure is maintained under acidic conditions, apoLp-III tertiary structure is altered, adopting molten globule-like characteristics. In studies of apoLp-III interaction with natural lipoproteins, we found that apoLp-III is readily displaced from the surface of L. migratoria low-density lipophorin by recombinant apoLp-III proteins from either L. migratoria or M. sexta. Thus, despite important differences between these two apoLp-IIIs (amino acid sequence, presence of carbohydrate), their functional similarity is striking. This similarity is also illustrated by the recently published NMR solution structure of M. sexta apoLp-III wherein its molecular architecture closely parallels that of L. migratoria apoLp-III.
Department of Chemistry and Biochemistry, California State University Long Beach, 1250 Bellflower Boulevard, Long Beach, CA 90840, USA. pweers@csulb.edu
Paul M M
PM
Weers
Robert O
RO
Ryan
D000818:Animals; D001053:Apolipoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D006031:Glycosylation; D006110:Grasshoppers / Q000378:metabolism; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism; D018402:Manduca / Q000378:metabolism; D008958:Models, Molecular; D010743:Phospholipids / Q000378:metabolism; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014461:Ultracentrifugation / Q000379:methods
D001053:Apolipoproteins; D008074:Lipoproteins; D010743:Phospholipids; D011994:Recombinant Proteins; C042470:apolipophorin III; D004134:Dimyristoylphosphatidylcholine