Apolipocrustacein, formerly vitellogenin, is the major egg yolk precursor protein in decapod crustaceans and is homologous to insect apolipophorin II/I and vertebrate apolipoprotein B

Abstract

Background: In animals, the biogenesis of some lipoprotein classes requires members of the ancient large lipid transfer protein (LLTP) superfamily, including the cytosolic large subunit of microsomal triglyceride transfer protein (MTP), vertebrate apolipoprotein B (apoB), vitellogenin (Vtg), and insect apolipophorin II/I precursor (apoLp-II/I). In most oviparous species, Vtg, a large glycolipoprotein, is the main egg yolk precursor protein.Results: This report clarifies the phylogenetic relationships of LLTP superfamily members and classifies them into three families and their related subfamilies. This means that the generic term Vtg is no longer a functional term, but is rather based on phylogenetic/structural criteria. In addition, we determined that the main egg yolk precursor protein of decapod crustaceans show an overall greater sequence similarity with apoLp-II/I than other LLTP, including Vtgs. This close association is supported by the phylogenetic analysis, i.e. neighbor-joining, maximum likelihood and Bayesian inference methods, of conserved sequence motifs and the presence of three common conserved domains: an N-terminal large lipid transfer module marker for LLTP, a DUF1081 domain of unknown function in their central region exclusively shared with apoLp-II/I and apoB, and a von Willebrand-factor type D domain at their C-terminal end. Additionally, they share a conserved functional subtilisin-like endoprotease cleavage site with apoLp-II/I, in a similar location. Conclusion:The structural and phylogenetic data presented indicate that the major egg yolk precursor protein of decapod crustaceans is surprisingly closely related to insect apoLp-II/I and vertebrate apoB and should be known as apolipocrustacein (apoCr) rather than Vtg. These LLTP may arise from an ancient duplication event leading to paralogs of Vtg sequences. The presence of LLTP homologs in one genome may facilitate redundancy, e.g. involvement in lipid metabolism and as egg yolk precursor protein, and neofunctionalization and subfunctionalization, e.g. involvement in clotting cascade and immune response, of extracellular LLTP members. These protein-coding nuclear genes may be used to resolve phylogenetic relationships among the major arthropod groups, especially the Pancrustacea-major splits.

Multifaceted biological insights from a draft genome sequence of the tobacco hornworm moth, Manduca sexta

“…MTP is needed for lipid loading during the assembly of apolipoprotein-B (apoB) containing lipoproteins in vertebrates (Sellers et al, 2003) and lipophorin in insects (Smolenaars et al, 2007a). Interestingly, the genes encoding ApoLp, LTP and MTP, are members of the large lipid transfer protein (LLTP) superfamily (Avarre et al, 2007; Smolenaars et al, 2007b). This family of proteins, which includes apoB, MTP and vitellogenin, could have originated from a vitellogenin precursor or an ancient MTP precursor (Sellers et al, 2005).…”

Identification of Receptor Ligands in Apo B100 Reveals Potential Functional Domains

“…Apo B100 is a member of the Large Lipid Transfer Protein (LLTP) superfamily, which includes vitellogenin-like LLTPs, vigilin, microsomal triglyceride transfer protein - MTPs (9, 10), and insect apolipophorins (11, 12). LLTP molecules are involved in extracellular transport of hydrophobic lipids and triglycerides (9, 10), binding nucleic acids (15–17), and appear to be involved in the immune response (12–14).…”

“…Apo B100 is a member of the large lipid transfer protein (LLTP) superfamily that includes microsomal triglyceride transfer protein (MTTP), vigilin, vitellogenins, and insect lipophorins (9–11). Non-apo B100 LLTPs are known to have multiple roles, including protein-protein interactions in immune response (12–14) and mRNA binding (15–17).…”

Pyroglyphid House Dust Mite Allergens

“…The ca 250 amino acid sequence that forms the beta barrel structure of the N-terminal lipid transfer module is highly conserved [48,117] and areas of sequence similarity can be identified throughout the first 800 amino acids of its 1760 residue sequence. It was originally described as an apolipophorin-like protein because of its similarity to published insect apolipophorins but these sequences are also similar to crustacean vitellogenins [118,119]. The subtilisinlike convertase cleavage site (RXR/KR) conserved at about residue 725 in the crustacean vitellogenins is however not present suggesting another function.…”

“…The lack of a sex difference indicates a function other than a vitellogenin. In a recent review of the LLTP family Avvare emphasised the diversity and lack of knowledge of the function of this family and the fact that the vitellogenins cannot be distinguished from the apolipophorin by sequence analysis [118]. IgE binding to LLTP antigens with high sequence identity to the group 14 allergens have also been described for scabies mite infection in humans [120] and sheep scab [121].…”