A lipid transfer particle in Musca domestica haemolymph

Lipid transfer particle from the silkworm, Bombyx mori, is a novel member of the apoB/large lipid transfer protein family

Lipid transfer particle (LTP) is a high-molecular-weight, very high-density lipoprotein known to catalyze the transfer of lipids between a variety of lipoproteins, including both insects and vertebrates. Studying the biosynthesis and regulation pathways of LTP in detail has not been possible due to a lack of information regarding the apoproteins. Here, we sequenced the cDNA and deduced amino acid sequences for three apoproteins of LTP from the silkworm (Bombyx mori). The three subunit proteins of the LTP are coded by two genes, apoLTP-II/I and apoLTP-III. ApoLTP-I and apoLTP-II are predicted to be generated by posttranslational cleavage of the precursor protein, apoLTP-II/I. Clusters of amphipathic secondary structure within apoLTP-II/I are similar to Homo sapiens apolipoprotein B (apoB) and insect lipophorins. The apoLTP-II/I gene is a novel member of the apoB/large lipid transfer protein gene family. ApoLTP-III has a putative conserved juvenile hormone-binding protein superfamily domain. Expression of apoLTP-II/I and apoLTP-III genes was synchronized and both genes were primarily expressed in the fat body at the stage corresponding to increased lipid transport needs. We are now in a position to study in detail the physiological role of LTP and its biosynthesis and assembly.

Structure and expression of the lipophorin-encoding gene of the malaria vector, Anopheles gambiae

Lipophorin is the major hemolymph protein responsible for lipid transport among tissues of insects. This protein may be a lipid source for the development and reproduction of human malaria parasites in mosquitoes, and therefore could be a target to disrupt malaria parasite development in the vector. The lipophorin of Anopheles gambiae was purified by KBr gradient ultracentrifugation and showed variation in density from 1.111 to 1.143 g/ml during development. The amount and density of lipophorin increase in blood-fed females, indicating an adaptation of vitellogenic mosquitoes to an elevated rate of lipid transport to the developing eggs. The A. gambiae lipophorin gene is composed of eight exons and transcribes an mRNA that is 10,516 nucleotides in length. The predicted initial translation product is a preproapoliphorin consisting of 3332 amino acids, which is processed by proteolysis to generate two mature apolipophorins: apolipophorin-I (Mr = 280,000) and apolipophorin-II (Mr = 81,000). The gene is expressed in the fat body tissues throughout development. An elevated transcriptional activity of the lipophorin gene during vitellogenesis is consistent with the presence of putative cis-regulatory elements (GATA and ecdysone responsive elements) in its 3'-end flanking DNA sequence.