Journal
INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY
Volume 36, Issue 4, Pages 231-240Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ibmb.2006.01.001
Keywords
apolipophorin III; apolipoprotein; lipophorin; lipid transport; innate immunity
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Funding
- NHLBI NIH HHS [HL 64159, HL 077135] Funding Source: Medline
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It has been one-quarter century since the identification of apolipophorin III (apoLp-III) as an important component of insect hemolymph lipid transport processes. Original studies of flight-related lipid transport that led to the discovery of apoLp-III have been followed by detailed studies of its structure and function relations, species distribution as well as its physiological roles beyond lipid transport. The non-exchangeable apoLp-I and -II, which are derived from a common precursor, are structural protein components of the multifunctional lipophorin particle. ApoLp-I/II have been identified as members of a broad lipid-binding protein family based on sequence similarities with their vertebrate counterparts. By contrast, apoLp-III can be found as a lipid-free hemolymph protein that associates with lipophorin during hormone-induced lipid mobilization. Based on structural characterization, apoLp-III belongs to a large family of exchangeable apolipoproteins characterized by segments of amphipathic a-helix. The remarkable structural adaptability of apoLp-III can be ascribed to its globular amphipathic a-helix bundle conformation wherein hydrophobic lipid-binding regions are stabilized in the absence of lipid by helix-helix interactions. Upon exposure to potential lipid surface-binding sites, the globular helix bundle opens to expose its hydrophobic interior permitting substitution of helix-helix contact in the bundle for helix-lipid interactions. Novel functions of apoLp-III beyond lipid transport have been identified recently. The expanding role of apoLp-III in innate immunity promises to offer exciting research opportunities in the future. (c) 2006 Elsevier Ltd. All rights reserved.
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