Polymorphic cDNAs encode for the methionine-rich storage protein from Manduca sexta

Improving Nutritional Quality of Plant Proteins Through Genetic Engineering

Humans and animals are unable to synthesize essential amino acids such as branch chain amino acids methionine (Met), lysine (Lys) and tryptophan (Trp). Therefore, these amino acids need to be supplied through the diets. Several essential amino acids are deficient or completely lacking among crops used for human food and animal feed. For example, soybean is deficient in Met; Lys and Trp are lacking in maize. In this mini review, we will first summarize the roles of essential amino acids in animal nutrition. Next, we will address the question: “What are the amino acids deficient in various plants and their biosynthesis pathways?” And: “What approaches are being used to improve the availability of essential amino acids in plants?” The potential targets for metabolic engineering will also be discussed, including what has already been done and what remains to be tested.

Expression and evolution of hexamerins from the tobacco hornworm, Manduca sexta, and other Lepidoptera

Hexamerins are large hemolymph-proteins that accumulate during the late larval stages of insects. Hexamerins have emerged from hemocyanin, but have lost the ability to bind oxygen. Hexamerins are mainly considered as storage proteins for non-feeding stages, but may also have other functions, e.g. in cuticle formation, transport and immune response. The genome of the hornworm Manduca sexta harbors six hexamerin genes. Two of them code for arylphorins (Msex2.01690, Msex2.15504) and two genes correspond to a methionine-rich hexamerin (Msex2.10735) and a moderately methionine-rich hexamerin (Msex2.01694), respectively. Two other genes do not correspond to any known hexamerin and distantly resemble the arylphorins (Msex2.01691, Msex2.01693). Five of the six hexamerin genes are clustered within ∼45 kb on scaffold 00023, which shows conserved synteny in various lepidopteran genomes. The methionine-rich hexamerin gene is located at a distinct site. M. sexta and other Lepidoptera have lost the riboflavin-binding hexamerin. With the exception of Msex2.01691, which displays low mRNA levels throughout the life cycle, all hexamerins are most highly expressed during pre-wandering phase of the 5th larval instar of M. sexta, supporting their role as storage proteins. Notably, Msex2.01691 is most highly expressed in the brain, suggesting a divergent function. Phylogenetic analyses showed that hexamerin evolution basically follows insect systematics. Lepidoptera display an unparalleled diversity of hexamerins, which exceeds that of other hexapod orders. In contrast to previous analyses, the lepidopteran hexamerins were found monophyletic. Five distinct types of hexamerins have been identified in this order, which differ in terms of amino acid composition and evolutionary history: i. the arylphorins, which are rich in aromatic amino acids (∼20% phenylalanine and tyrosine), ii. the distantly related arylphorin-like hexamerins, iii. the methionine-rich hexamerins, iv. the moderately methionine rich hexamerins, and v. the riboflavin-binding hexamerins.

Expression of a cDNA encoding a member of the hexamerin storage proteins from the moth Sesamia nonagrioides (Lef.) during diapause

We isolated and sequenced a cDNA clone corresponding to a storage protein (SnoSP1) from the corn stalk borer Sesamia nonagrioides (Lef.). The cDNA for SnoSP1 (2403 bp) codes for a 751 residue protein with predicted molecular mass of 88.3 kDa and calculated isoelectric point pI=8.72. A signal peptide of 16 amino acids is present at the N-terminus and the protein contained conserved insect larval storage protein signature sequence patterns. Multiple alignment analysis of the amino acid sequence revealed that SnoSP1 is most similar to the basic juvenile hormone-suppressible protein 2 precursor (TniSP2) from Trichoplusia ni (71% identity) and other moderately methionine-rich hexamers. According to both phylogenetic analyses and the criteria of amino acid composition, SnoSP1 belongs to the subfamily of moderately methionine-rich storage proteins (3.7% methionine, 11% aromatic amino acid). Treatment with the juvenile hormone analog, methroprene, after head ligation of larvae, is found to suppress the level of SnoSP1 gene, indicating hormonal effects at the transcriptional level. We also examined developmental profiles of SnoSP1 expression in fat body from diapausing and non-diapausing larvae by semi-quantitative and Real-Time PCR assays. In non diapause conditions the abundance of SnoSP1 was found in high levels during the last larval stage and decreased gradually during the pupal stage. Very low levels of this mRNA were detected in larvae that were preparing to enter diapause, but mRNA dramatically increased in those that were in diapause as well as in those that terminate diapause.

Molecular cloning, expression, and characterization of a cDNA encoding the arylphorin-like hexameric storage protein from the mulberry longicorn beetle, Apriona germari

We describe here the cloning, expression, and characterization of a cDNA encoding the arylphorin-like hexameric storage protein from the mulberry longicorn beetle, Apriona germari (Coleoptera, Cerambycidae). The complete cDNA sequence of A. germari hexamerin (AgeHex) is comprised of 2,160 bp with 720 amino acid residues. The deduced protein sequence of AgeHex is most similar to Tenebrio molitor hexamerin2 (65.3%). Phylogenetic analysis further confirmed the AgeHex is more closely related to T. molitor hexmerin2 and T. molitor early-staged encapsulation inducing protein than to the other insect storage proteins. Southern blot analysis suggested the presence of A. germari hexamerin gene as a single copy and Northern blot analysis confirmed fat body-specific expression at the transcriptional level. The cDNA encoding AgeHex was expressed as a 80-kDa protein in the baculovirus-infected insect cells. Western blot analysis using the polyclonal antiserum against recombinant AgeHex indicated that the AgeHex corresponds to storage protein 2 (SP2) present in the A. germari larval hemolymph.

Two juvenile hormone suppressible storage proteins may play different roles in Hyphantria cunea Drury

We isolated and sequenced cDNA clones corresponding to two storage proteins (HcSP-1 and HcSP-2) from fall webworm, Hyphantria cunea. The cDNAs for HcSP-1 (2,337 bp) and HcSP-2 (2,572 bp) code for 753 and 747 residue proteins with predicted molecular masses of 88.3 and 88.5 kDa, respectively. The calculated isoelectric points are pI = 8.4 (HcSP-1) and 7.6 (HcSP-2). Multiple alignment analysis of the amino acid sequence revealed that HcSP-1 is most similar to SL-1 from S. litura (73.8% identity) and other methionine-rich hexamers, whereas HcSP-2 is most similar to the SL-2 alpha subunit from S. litura (74.8% identity) and other moderately methionine-rich hexamers. The two storage proteins from H. cunea shared only 38.4% identity with one another. According to both phylogenetic analyses and the criteria of amino acid composition, HcSP-1 belongs to the subfamily of Met-rich storage proteins (6% methionine, 10% aromatic amino acid), and HcSP-2 belongs to the subfamily of moderately methionine-rich storage proteins (3.2% methionine, 12.9% aromatic amino acid). Topical application of the JH analog, methoprene, after head ligation of larvae, suppressed transcription of the SP genes, indicating hormonal effects at the transcriptional level. The HcSP-1 transcript was detected by Northern blot analysis in Malpighian tubule, testis, and ovary, in addition to fat body where it was most abundant. The HcSP-2 transcript was detected only in fat body and Malpighian tubule. The accumulation of HcSP-1 in ovary and HcSP-2 in Malpighian tubule might be related to differential functions in both organs.

cDNA sequences and mRNA levels of two hexamerin storage proteins PinSP1 and PinSP2 from the Indianmeal moth, Plodia interpunctella

In insects, storage proteins or hexamerins accumulate apparently to serve as sources of amino acids during metamorphosis and reproduction. Two storage protein-like cDNAs obtained from a cDNA library prepared from fourth instar larvae of the Indianmeal moth (Plodia interpunctella) were cloned and sequenced. The first clone, PinSP1, contained 2431 nucleotides with a 2295 nucleotide open reading frame (ORF) encoding a protein with 765 amino acid residues. The second cDNA, PinSP2, consisted of 2336 nucleotides with a 2250-nucleotide ORF encoding a protein with 750 amino acid residues. PinSP1 and PinSP2 shared 59% nucleotide sequence identity and 44% deduced amino acid sequence identity. A 17-amino acid signal peptide and a molecular mass of 90.4 kDa were predicted for the PinSP1 protein, whereas a 15-amino acid signal peptide and a mass of 88 kDa were predicted for PinSP2. Both proteins contained conserved insect larval storage protein signature sequence patterns and were 60-70% identical to other lepidopteran larval storage proteins. Expression of mRNA for both larval storage proteins was determined using the quantitative reverse transcription polymerase chain reaction method. Only very low levels were present in the second instar, but both mRNAs dramatically increased during the third instar, peaked in the fourth instar, decreased dramatically late in the same instar and pupal stages, and were undetectable during the adult stage. Males and females exhibited similar mRNA expression levels for both storage proteins during the pupal and adult stages. The results support the hypothesis that P. interpunctella, a species that does not feed after the larval stage, accumulates these two storage proteins as reserves during larval development for subsequent use in the pupal and adult stages.

Complete sequence, expression, and evolution of the hexamerin LSP-2 of Calliphora vicina

In cyclorraphan Diptera, two different types of hemolymph proteins exist which belong to the hexamerin family. During the last larval instar, Calliphora vicina synthesizes, besides the major fraction of arylphorin, a second hexameric protein, LSP-2. Here the developmentally regulated biosynthesis of this protein was analyzed. Western blot analyses showed that LSP-2 is not present in eggs, 1st, and 2nd instar larvae, whereas it can be detected in all tissues of last instar larvae. We report the characterization of the complete cDNA sequence that encodes a LSP-2 subunit, a nascent polypeptide of 701 amino acids with a molecular mass of 83.16 kDa. By Northern blotting, a mRNA of about 2.2 kb coding for LSP-2 is identified exclusively in the fat body of 3rd larval instars reflecting the stage and tissue specificity of LSP-2 gene expression. Phylogenetic analysis demonstrates the existence of two distinct groups of hexamerins in Diptera.

The Drosophila Lsp-1 beta gene. A structural and phylogenetic analysis

In Drosophila melanogaster, metamorphosis and reproduction are thought to be supported in large by two immunologically distinct hexameric storage proteins (hexamerins), larval serum protein 1 (LSP-1), a mixed hexamer of three closely related subunits, Lsp-1 (alpha, beta and gamma) and larval serum protein 2 (LSP-2), a homohexamer of Lsp-2 subunits. To understand the structural and functional differences between these two storage hexamers, the nucleotide sequence of the coding region of the Lsp-1 beta gene was determined for comparison with LSP-2 and a number of other arthropod hexamerins. The G + C content of the coding sequence is 55%, with 92.8% of the codons containing G or C in the third position. Conceptual translation of the Lsp-1 beta open reading frame revealed a 789-amino-acid polypeptide of 94465 Da. The amino acid sequence of Lsp-1 beta is 65.8% identical to that of calliphorin, the major hexamerin of the blowfly, Calliphora vicina, and only 35.2% identical to Drosophila Lsp-2. This greater similarity to calliphorin is also reflected in high aromatic amino acid and methionine contents, in contrast to LSP-2 which is enriched to a lesser extent only in aromatic amino acids. Lsp-1 beta is also more closely related to calliphorin with respect to the protein domain structure, the presence of a single intron in its gene, and the absence of glycosylation sites. However, phylogenetic analysis based on multiple alignments revealed that LSP-1 calliphorin and LSP-2 form a distinct dipteran clade whose members are more similar to each other than to any previously sequenced lepidopteran hexamerin or arthropod hemocyanin.

Common origin of arthropod tyrosinase, arthropod hemocyanin, insect hexamerin, and dipteran arylphorin receptor

Dipteran arylphorin receptors, insect hexamerins, cheliceratan and crustacean hemocyanins, and crustacean and insect tyrosinases display significant sequence similarities. We have undertaken a systematic comparison of primary and secondary structures of these proteins. On the basis of multiple sequence alignments the phylogeny of these proteins was investigated. Hexamerin subunits, hemocyanin subunits, and tyrosinases share extensive similarities throughout the entire amino acid sequence. Our studies suggest the origin of arthropod hemocyanins from ancient tyrosinase-like proteins. Insect hexamerins likely evolved from hemocyanins of ancient crustaceans, supporting the proposed sister-group position of these subphyla. Arylphorin receptors, responsible for incorporation of hexamerins into the larval fat body of diptera, are related to hexamerins, hemocyanins, and tyrosinase. The receptor sequences display extensive similarities to the first and third domains of hemocyanins and hexamerins. In the middle region only limited amino acid conservation was observed. Elements important for hexamer formation are deleted in the receptors. Phylogenetic analysis indicated that dipteran arylphorin receptors diverged from ancient hexamerins, probably early in insect evolution.