Complete cDNA and gene sequence of the developmentally regulated arylphorin of Calliphora vicina and its homology to insect hemolymph proteins and arthropod hemocyanins

The lymphatic vascular system: much more than just a sewer

Almost 400 years after the (re)discovery of the lymphatic vascular system (LVS) by Gaspare Aselli (Asellius G. De lactibus, sive lacteis venis, quarto vasorum mesaraicorum genere, novo invento Gasparis Asellii Cremo. Dissertatio. (MDCXXIIX), Milan; 1628.), structure, function, development and evolution of this so-called 'second' vascular system are still enigmatic. Interest in the LVS was low because it was (and is) hardly visible, and its diseases are not as life-threatening as those of the blood vascular system. It is not uncommon for patients with lymphedema to be told that yes, they can live with it. Usually, the functions of the LVS are discussed in terms of fluid homeostasis, uptake of chylomicrons from the gut, and immune cell circulation. However, the broad molecular equipment of lymphatic endothelial cells suggests that they possess many more functions, which are also reflected in the pathophysiology of the system. With some specific exceptions, lymphatics develop in all organs. Although basic structure and function are the same regardless their position in the body wall or the internal organs, there are important site-specific characteristics. We discuss common structure and function of lymphatics; and point to important functions for hyaluronan turn-over, salt balance, coagulation, extracellular matrix production, adipose tissue development and potential appetite regulation, and the influence of hypoxia on the regulation of these functions. Differences with respect to the embryonic origin and molecular equipment between somatic and splanchnic lymphatics are discussed with a side-view on the phylogeny of the LVS. The functions of the lymphatic vasculature are much broader than generally thought, and lymphatic research will have many interesting and surprising aspects to offer in the future.

Diapause-specific gene expression in Calliphora vicina (Diptera: Calliphoridae)--a useful diagnostic tool for forensic entomology

Estimating the post mortem interval (PMImin) by age determination of blow fly larvae has been well-established for moderate temperatures. Low-temperature developmental data is only available sparsely and usually does not take overwintering strategies into account. The blow fly Calliphora vicina hibernates by diapausing in the third larval stage extending the duration of this developmental stage up to several weeks or even months. As the diagnosis of the diapause status is not possible by morphological characteristics, PMImin estimations might be biased during the cold season if only based on age determination of third instar larvae of C. vicina. Molecular markers were searched for which allows one to identify diapause in larvae. Expression analysis of 19 genes was performed in diapausing and non-diapausing larvae. Three genes encoding for heat shock proteins (hsp23, hsp24 and hsp70) were found to be up-regulated distinctly in diapausing larvae and at 1 day in non-diapausing larvae. If several larvae are subjected to an analysis, a high variance in the expression level of the gene encoding for the anterior fat body protein is a further marker for diapause. The present study proves the potential use of gene expression analysis as a suitable diagnosis tool for diapause in C. vicina.

Life history plasticity after attaining a dietary threshold for reproduction is associated with protein storage in flesh flies

Body condition affects the timing and magnitude of life history transitions. Therefore, identifying proximate mechanisms involved in assessing condition is critical to understanding how these mechanisms affect the expression of life history plasticity. Nutrient storage is an important body condition parameter, likely playing roles in both attaining minimum body-condition thresholds for life history transitions and expression of life history traits.We manipulated protein availability for females of the flesh fly Sarcophaga crassipalpis to determine whether reproductive timing and output would remain plastic or become fixed. Liver was provided for 0, 2, 4, or 6 days of adult pre-reproductive development. Significantly, liver was removed after the feeding threshold had been attained and females had committed to producing a clutch.We also identified the major storage proteins and monitored their abundances, because protein stores may serve as an index of body condition and therefore may play an important role in life history transitions and plasticity.Flesh flies showed clear post-threshold plasticity in reproductive timing. Females fed protein for 2 days took ~30% longer to provision their clutch than those fed for 4 or 6 days. Observations of oogenesis showed the 2-day group expressed a different developmental program including slower egg provisioning.Protein availability also affected reproductive output. Females fed protein for 2 days produced ~20% fewer eggs than females fed 4 or 6 days. Six-day treated females provisioned larger eggs than 4-day treated females, followed by 2-day treated females with the smallest eggs.Two storage proteins were identified, LSP-1 and LSP-2. LSP-2 accumulation differed across feeding treatments. The 2- and 4-day treatment groups accumulated LSP-2 stores but depleted them during provisioning of the first clutch, whereas the 6-day group accumulated the greatest quantity of LSP-2 and had substantial LSP-2 stores remaining at the end of the clutch. This pattern of accumulation and depletion suggests that LSP-2 could play roles in both provisioning the current clutch and future clutches, making it a good candidate molecule for affecting reproductive timing and allotment. LSP-1 was not associated with post-threshold plasticity; it was carried over from larval feeding into adulthood and depleted uniformly across all feeding groups.

The non-dosage compensated Lsp1alpha gene of Drosophila melanogaster escapes acetylation by MOF in larval fat body nuclei, but is flanked by two dosage compensated genes

BACKGROUND

In Drosophila melanogaster dosage compensation of most X-linked genes is mediated by the male-specific lethal (MSL) complex, which includes MOF. MOF acetylates histone H4 at lysine 16 (H4K16ac). The X-linked Larval serum protein one alpha (Lsp1alpha) gene has long been known to be not dosage compensated. Here we have examined possible explanations for why the Lsp1alpha gene is not dosage compensated.

RESULTS

Quantitative RNase protection analysis showed that the genes flanking Lsp1alpha are expressed equally in males and females and confirmed that Lsp1alpha is not dosage compensated. Unlike control X-linked genes, Lsp1alpha was not enriched for H4K16ac in the third instar larval fat body, the tissue in which the gene is actively expressed. X-linked Lsp1alpha promoter-lacZ reporter transgenes are enriched for H4K16ac in third instar larval fat body. An X-linked reporter gene bracketed by Lsp1alpha flanking regions was dosage compensated. One of the genes flanking Lsp1alpha is expressed in the same tissue. This gene shows a modest enrichment for H4K16ac but only at the part of the gene most distant from Lsp1alpha. Phylogenetic analyses of the sequences of the genomes of 12 Drosophila species shows that Lsp1alpha is only present within the melanogaster subgroup of species.

CONCLUSION

Lsp1alpha is not modified by the MSL complex but is in a region of the X chromosome that is regulated by the MSL complex. The high activity or tissue-specificity of the Lsp1alpha promoter does not prevent regulation by the MSL complex. The regions flanking Lsp1alpha do not appear to block access by the MSL complex. Lsp1alpha appears to have recently evolved within the melanogaster subgroup of Drosophila species. The most likely explanation for why Lsp1alpha is not dosage compensated is that the gene has not evolved a mechanism to independently recruit the MSL complex, possibly because of its recent evolutionary origin, and because there appears to be a low level of bound MSL complex in a nearby gene that is active in the same tissue.

Duplicative and conservative transpositions of larval serum protein 1 genes in the genus Drosophila

Interspecific comparative molecular analyses of transposed genes and their flanking regions can help to elucidate the time, direction, and mechanism of gene transposition. In the Drosophila melanogaster genome, three Larval serum protein 1 (Lsp1) genes (alpha, beta and gamma) are present and each of them is located on a different chromosome, suggesting multiple transposition events. We have characterized the molecular organization of Lsp1 genes in D. buzzatii, a species of the Drosophila subgenus and in D. pseudoobscura, a species of the Sophophora subgenus. Our results show that only two Lsp1 genes (beta and gamma) exist in these two species. The same chromosomal localization and genomic organization, different from that of D. melanogaster, is found in both species for the Lsp1beta and Lsp1gamma genes. Overall, at least two duplicative and two conservative transpositions are necessary to explain the present chromosomal distribution of Lsp1 genes in the three Drosophila species. Clear evidence for implication of snRNA genes in the transposition of Lsp1beta in Drosophila has been found. We suggest that an ectopic exchange between highly similar snRNA sequences was responsible for the transposition of this gene. We have also identified the putative cis-acting regulatory regions of these genes, which seemingly transposed along with the coding sequences.

Spider hemocyanin binds ecdysone and 20-OH-ecdysone

Fluorescence quenching studies and binding experiments with [(3)H]ecdysone reveal that the respiratory protein, hemocyanin, of the tarantula Eurypelma californicum binds ecdysone. The binding constant for ecdysone ranges between 0.5 and 5 mM, indicating a low affinity binding. However, it is comparable with those found for the ecdysone binding to hexamerins from insects. Based on a comparison of sequences and x-ray structures of arthropodan hemocyanins, we propose an evolutionary conserved hydrophobic pocket in domain 1 of the hemocyanin subunit that may bind ecdysone.

The origin, transport and cleavage of the molt-associated cuticular protein CECP22 from Calpodes ethlius (Lepidoptera, Hesperiidae)

CECP22 (Calpodes ethlius Cuticular Protein 22 kDa) is a molt associated protein found in the cuticle of C. ethlius larvae and pupae. The mRNA for the CECP22 cuticular protein is expressed in the epidermis and fat body during the intermolt. The protein itself accumulates in intermolt hemolymph, but at molting, when the cuticle is being digested, it is also found in the cuticle of surface integument, tracheae, foregut and hindgut and in the molting fluid. CECP22 exists in two forms. The large form (19.17 kDa, pI 6.2) becomes smaller (16.1 kDa, pI 7.4) by cleavage at the proteolytic cleavage site (position 170) with amidation of the C-terminal. The small, more basic peptide, appears only at molting, first in the cuticle and then in the molting fluid. It is presumed to be the active form of an amidase involved in the earliest stages of cuticle degradation. The inactive form accumulates in the hemolymph during the long intermolt and probably represents an abundant source of precursor enzyme that can be provided to all cuticle containing organs for a precise initiation of cuticle degradation.

Molecular cloning and expression of two hexamerin cDNAs from the mosquito, Aedes aegypti

Fourth-instar larvae of Aedes aegypti synthesize two types of hexamerins, Hexamerin-1 (AaHex-1) and Hexamerin-2 (AaHex-2), whose subunits are distinguished by different methionine and aromatic amino acid contents. In early female pupae only the methionine-rich AaHex-1gamma subunit accumulates to two-fold higher levels than in males. To investigate the relationship between hexamerin structure and the roles of Hex-1 and Hex-2 during mosquito development and reproduction, we have cloned and sequenced cDNAs encoding the AaHex-2alpha, -2beta and AaHex-1gamma subunits. Comparison with other insect hexamerins revealed that the Aedes Hex-1 and Hex-2 proteins belong, respectively, to the two hexamerin subfamilies previously defined for brachyceran Diptera. Probes specific for the Hex-2alpha and Hex-1gamma transcripts showed that expression of both genes follows the same developmental timetable. However, greater Hex-1gamma mRNA accumulation may contribute to the higher levels of Hex-1 gamma protein in early female pupae.

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.

Sequence and developmental expression of Cyp18, a member of a new cytochrome P450 family from Drosophila

Preliminary studies of a partial cDNA clone of the Eig17-1 gene from Drosophila melanogaster have shown that it encodes a probable cytochrome P450 of unknown function. To further characterize the Eig17-1 gene product, a full-length cDNA clone was isolated from a late-larval cDNA library and sequenced. Eig17-1 encodes a protein of 538 amino acids. The predicted protein is a cytochrome P450 that has been assigned to a new family, CYP18. The CYP18 protein is most closely related to steroid and xenobiotic metabolizing P450s of family CYP2 (30-33% identity), and to vertebrate steroidogenic P450s of families CYP17 and CYP21 (25-28% identity). Developmental Northern blot analysis revealed five distinct periods of Cyp18 expression during postembryonic development. Each period lasted 12-15 h, and was tightly correlated with reported ecdysteroid pulses in the first, second and third larval instars, at the time of pupariation and in pupae. This pattern of expression is consistent with the known induction of Cyp18 transcription by 20-hydroxyecdysone at the time of pupariation and suggests that ecdysteroids are major regulators of Cyp18 expression throughout postembryonic development. Northern blot analysis of RNA isolated from different prepupal tissues indicates that Cyp18 is differentially expressed in various ecdysteroid-responsive tissues. High Cyp18 expression was observed in body wall and gut while negligible expression was observed in salivary glands and fat body.

Molecular cloning and expression of a hexamerin cDNA from the malaria mosquito, Anopheles gambiae

During the last larval instar, dipteran insects synthesize two hexamerins rich in aromatic residues, typified by the larval serum proteins 1 and 2 (LSP-1 and LSP-2) of Drosophila melanogaster. We report here the characterization of a complete cDNA sequence encoding a LSP-1-like protein from a lower dipteran insect, the malaria mosquito Anopheles gambiae. The cDNA encodes the subunit of a homohexamer, A. gambiae hexamerin-1.1 (AgHex-1.1), which is a major pupal protein but only a minor constituent of late larval hemolymph. AgHex-1.1 is moderately rich in methionine (3.9%) and particularly rich in aromatic residues (21% Phe+Tyr). Cytogenetic analysis reveals AgHex-1.1 to be encoded by a single-copy gene localized to division 22F within the proximal 2La inversion breakpoint of chromosome 2 of A. gambiae. The AgHex-1.1 transcript is first detected in fourth-instar larvae (L4) and disappears abruptly in early pupae. In situ hybridization shows accumulation of the transcript uniquely in the larval fat body. AgHex-1.1 mRNA is re-expressed in male and female adults at about 10% of the L4 level, with no effect of bloodfeeding in females. The potential roles of AgHex-1.1 in Anopheles development and reproductive maturation are discussed.

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.

Sequence, structure and evolution of the ecdysone-inducible Lsp-2 gene of Drosophila melanogaster

The Lsp-2 gene encodes a major larval serum protein (hexamerin) of Drosophila melanogaster. Transcription of Lsp-2 is controlled by 20-hydroxyecdysone. Here we report the analysis of the structure of the Lsp-2 gene including the adjacent 5' and 3' sequences. In contrast to all other known hexamerin genes, Lsp-2 does not contain an intron. The Lsp-2 mRNA measures 2312 bases, as deduced from experimental determination of the transcription-start and stop sites and conceptual translation results in a 718 amino acid hexamerin subunit, including a 21-amino-acid signal peptide. While the calculated molecular mass of the native 697-amino-acid subunit is 83.5 kDa, mass spectrometry gave a value of 74.5 kDa. We detected in the Lsp-2 gene a 2052-bp antisense ORF that probably does not code for any protein. An unusual accumulation of rarely used codon triplets was found at the 5' and 3' ends of the Lsp-2 ORF. The calculated secondary structure matches well with that of arthropod hemocyanins. Electron micrographs show for LSP-2 hexamers a cubic shape, which can not be easily reconciled with its hexameric structure. Phylogenetic analysis revealed that LSP-2 diverged from the LSP-1 like hexamerins after separation of the Diptera from other insect orders.

Conservation of hexamerin endocytosis in Diptera

In cyclorrhaphan Diptera at least two different types of haemolymph proteins exist which belong to the class of hexamerins. In the last larval instar of Calliphora vicina, the highly aromatic hexamerin, arylphorin, and the second hexamerin, PII, make up about 90% of haemolymph proteins. Both of these proteins are selectively taken up by the fat body cells at the end of larval life and share a common membrane-bound receptor. In addition, hexamerins and possible hexamerin receptors of Calliphora vicina, Calliphora vomitoria, Drosophila melanogaster, Ceratitis capitata, Sarcophaga bullata, Musca domestica and Protophormia terraenovae were investigated. Uptake of arylphorin by the larval fat bodies of Calliphora vicina as well asarylphorin-receptor binding can be competed in vitro by haemolymph from other Diptera. Therefore, hexamerin-receptor binding must be conserved among related cyclorrhaphan Diptera and between different types of hexamerins within a species. As the degree of competition is in good agreement with the presumed phylogenetic distances between these species, the method described here provides a simple tool to estimate evolutionary distances.

Insect storage proteins: gene families and receptors

The accumulation and utilization of storage proteins are prominent events linked to the metamorphosis of holometabolous insects. Storage proteins are synthesized in fat body, secreted into the larval hemolymph and taken up by fat body shortly before pupation. Within the pupal fat body, these proteins are initially stored in protein granules, and later proteolytically broken down to supply amino acid resources necessary for the completion of adult development. Most, but not all storage proteins belong to a superfamily of hexameric larval serum proteins that are evolutionarily related to hemocyanin. This article reviews the classification of these proteins, based on their amino acid sequences, and the current knowledge of the receptors that mediate their selective uptake into pupal fat body.

Sequencing analysis of cDNA clones encoding the American cockroach Cr-PI allergens. Homology with insect hemolymph proteins

A previous article described the isolation of several lambdagt22A cDNA clones expressing the American cockroach (Periplaneta americana) Cr-PI allergens recognized by both human atopic IgE antibodies and anti-Cr-PI monoclonal antibodies (Wu, C. H., Lee, M. F., and Liao, S. C.(1995) J. Allergy Clin. Immunol. 96, 352-359). This article presents the nucleotide and deduced amino acid sequences of two cDNA clones encoding major allergens of P. americana. Clones C12 and C20 encode proteins of 685 and 631 amino acids with two potential N-glycosylation sites each. The predicted molecular weights for C12 and C20 cloned proteins are 79,300 and 75, 500 with isoelectric point values of 6.26 and 6.63, which are compatible with the determined sizes (Mr 78,000 and 72,000) and isoelectric point value (6.2) of the Cr-PI allergens of P. americana. A high degree of identity (69.1%), including several overlapped predicted central antigenic determinant residues, was found between two allergens. The anti-fusion protein antibody-based enzyme-linked immunosorbent assay was able to detect crude American cockroach extract, Cr-PI, recombinant proteins, and commercial cockroach extracts, which provides further evidence that two allergens share common antigen determinants. Recombinant allergens of clones C12 and C20 both showed 47.4% skin reactivities on 19 cockroach-sensitive asthmatic patients. Unexpectedly, although no sequence similarity was found to other known allergens, two aromatic amino acid-rich allergens were found to have a striking sequence identity to insect storage proteins (20.1-33.9%), insect juvenile hormone-suppressible proteins (30.9-36.4%), and arthropod hemocyanins (29.7-34.6%). Results suggested that two prominent allergens of P. americana are ancestrally related to these insect hemolymph proteins and represent a new group of proteins in the hemocyanin superfamily. These data will now facilitate epitope-mapping studies, and the recombinant allergens may be valuable for diagnostic and therapeutic purposes.

Detection and quantification of a very high density lipoprotein in different tissues of Triatoma infestans during the last nymphal and adult stages

The presence of a very high density lipoprotein (VHDL), an hexameric protein, was explored in different tissues of Triatoma infestans throughout the last nymphal and adult stages, and in egg extracts by Western blot assays. The VHDL was always detected in both, hemolymph and fat body, during the above mentioned stages and it was also observed in the buffer soluble fraction of testis and egg homogenates. An enzyme-linked immunosorbent assay (ELISA) was used to measure the VHDL titer in these tissues. Hemolymph VHDL reaches a maximum value before the last molt, then it abruptly declines in males and females just after emergence, but during adult life it increases again. Fat body VHDL decreases slowly and continuously during the nymph growth reaching a minimum value prior to molting, and in the first week of adult life the values were even two-fold lower; then, it shows a different cycle of accumulation and depletion in males and females. In adult testis the VHDL undergoes a cycle similar to the one observed in male fat body. This protein increases progressively during embryonic development and, at the time of larval hatching it reaches its maximum value. The hexameric protein presents homologies in its N-terminal sequence with storage hexamerins of Diptera, Lepidoptera and Hymenoptera.

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.

The prophenoloxidase from the wax moth Galleria mellonella: purification and characterization of the proenzyme

A prophenoloxidase (PPO) was purified from the hemolymph of the larvae of Galleria mellonella. A 135-fold purification of the proenzyme with 25% yield was achieved by a combination of different chromatographic methods. An alternative micropreparation of pure PPO by a novel method for native electrophoresis in polyacrylamide gel is also described. The molecular mass of the native PPO was estimated to be 300 kDa by the pore-limit gradient electrophoresis in polyacrylamide gel. In the presence of sodium dodecyl sulphate, two closely migrating subunits of 80 and 83 kDa were detected under non-reducing conditions. The PPO was shown to be a glycoprotein and its isoelectric point was 6.2. The amino-acid composition of the purified protein was similar to the PPO from Bombyx mori. The monospecific antibody raised against the purified PPO crossreacted with the (pro)phenoloxidase in hemolymph of Manduca sexta. The activation of the PPO with chymotrypsin was investigated and two proteins of 67 and 50 kDa were found to be products of the proteolytic cleavage. The N-terminus of the G. mellonella PPO was blocked, but eleven partial internal sequences were determined after fragmentation of the purified PPO with trypsin. Three of these peptides exhibited significant homology with highly conserved sequences found in arthopod hemocyanins and insect storage proteins, which indicates that the PPO belongs to this family.

Complete cDNA-sequence of the receptor responsible for arylphorin uptake by the larval fat body of the blowfly, Calliphora vicina

In late larvae of the blowfly Calliphora vicina the storage protein arylphorin is selectively taken up by the fat body cells from the haemolymph. We have demonstrated that arylphorin incorporation is mediated by a specific membrane-bound receptor which is activated by 20-hydroxyecdysone. In this study we report the construction of a cDNA expression library from mRNA isolated from 8-day-old Calliphora larvae. Using affinity-purified antibodies against the arylphorin receptor we identified two cDNA clones of 4044 and 4043 bp, respectively. Both clones code for a 1253 amino acid protein with a deduced molecular mass of 142 kDa, the potential arylphorin receptor precursor, as confirmed by immunoprecipitation of translation products in vitro. Southern blot analysis indicated a single copy gene with multiple alleles; Northern blotting revealed a single mRNA of about 4.5 kb that appeared stage specifically from day 4 to day 8 during larval development. The deduced amino acid sequence exhibits significant similarities to arylphorin, the ligand, as well as to Fbp 1, the product of an ecdysteroid-inducible gene in Drosophila melanogaster larval fat body.

Insect cuticular proteins

Insect cuticles are composite structural materials with mechanical properties optimal for their biological functions. The bulk properties of cuticles are to a large extent determined by the interactions between the various components, mainly the chitin filament system and the proteins. The various cuticular types show pronounced differences in mechanical properties, and it is suggested that these differences can be related to the properties of the individual proteins and to the degree of secondary stabilization (sclerotization). The amino acid sequences, which have been obtained for insect cuticular proteins either by direct sequencing of purified proteins or by deduction from corresponding DNA-sequences, are listed according to insect order and species. Extensive sequence similarity is observed among several cuticular proteins obtained from different insect orders. Other cuticular proteins are characterized by repeated occurrence of a few small motifs consisting mainly of hydrophobic residues. The latter group of proteins has so far only been reported from stiff cuticles. The possible relevance of the various motifs and repeats for protein interaction and the mechanical properties of cuticles is discussed.

Crystal structure of deoxygenated Limulus polyphemus subunit II hemocyanin at 2.18 A resolution: clues for a mechanism for allosteric regulation

The crystal structure of Limulus polyphemus subunit type II hemocyanin in the deoxygenated state has been determined to a resolution of 2.18 A. Phase information for this first structure of a cheliceratan hemocyanin was obtained by molecular replacement using the crustacean hemocyanin structure of Panulirus interruptus. The most striking observation in the Limulus structure is the unexpectedly large distance of 4.6 A between both copper ions in the oxygen-binding site. Each copper has approximate trigonal planar coordination by three histidine N epsilon atoms. No bridging ligand between the copper ions could be detected. Other important new discoveries are (1) the presence of a cis-peptide bond between Glu 309 and Ser 310, with the carbonyl oxygen of the peptide plane hydrogen bonded to the N delta atom of the copper B ligand His 324; (2) localization of a chloride-binding site in the interface between the first and second domain; (3) localization of a putative calcium-binding site in the third domain. Furthermore, comparison of Limulus versus Panulirus hemocyanin revealed considerable tertiary and quaternary rigid body movements, although the overall folds are similar. Within the subunit, the first domain is rotated by about 7.5 degrees with respect to the other two domains, whereas within the hexamer the major movement is a 3.1 degrees rotation of the trimers with respect to each other. The rigid body rotation of the first domain suggests a structural mechanism for the allosteric regulation by chloride ions and probably causes the cooperative transition of the hexamer between low and high oxygen affinity states. In this postulated mechanism, the fully conserved Phe49 is the key residue that couples conformational changes of the dinuclear copper site into movements of the first domain.

Identification of two storage hexamers in the ant, Camponotus festinatus: accumulation in adult queenless workers

Two electrophoretically and immunologically distinct storage hexamers (Hex 1 and Hex 2) have been identified in Camponotus festinatus workers. The molecular weights of the native molecules were estimated to be 460,000 (Hex 1) and 580,000 (Hex 2) by pore limiting gradient electrophoresis. Hex 1 partially dissociates with moderate alkaline pH. Both proteins are composed of a single type of apoprotein of approx. 73 (Hex 1) and 80 kDa (Hex 2). While most of Hex 2 is sequestered by the fat body before pupation, Hex 1 remains largely in the hemolymph during the last larval and pupal stages. Both proteins were detected only in low concentrations in the hemolymph of newly emerged adults, and they gradually disappear from adult workers maintained in the colonies. In queenless workers, however, Hex 1 and Hex 2 accumulate in the hemolymph and fat body, constituting the most abundant proteins together with vitellogenin. Camponotus festinatus storage hexamers bear some homologies in their N-terminal sequence with the arylphorins of Diptera and Lepidoptera, as well as with a crab hemocyanin. However, with respect to their amino acid composition, they can not be classified as arylphorins.

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

By cDNA cloning and sequencing we have shown that Manduca sexta larvae produce three very closely related methionine-rich storage proteins, MMR1, MMR2 and MMR3. Out of 2256 nucleotides in the coding region, the cDNAs differ by at most twenty-one bases and this leads to a single amino acid difference between MMR1 and MMR2, and between MMR2 and MMR3, whereas MMR1 and MMR3 differ by two amino acids. Using both distance and parsimony methods, similarities between the M. sexta and Bombyx mori methionine-rich and arylphorin storage proteins were examined. Homologous proteins from the two species tend to be more closely related than are the two classes of storage proteins in a single species.

Quaternary and subunit structure of Calliphora arylphorin as deduced from electron microscopy, electrophoresis, and sequence similarities with arthropod hemocyanin

Arylphorin was purified from larvae of the blowfly Calliphora vicina and studied in its oligomeric form and after dissociation at pH 9.6 into native subunits. In accordance with earlier literature, it was electrophoretically shown to be a 500 kDa hexamer (1 x 6) consisting of 78 kDa polypeptides (= subunits). Electron micrographs of negatively stained hexamers show a characteristic curvilinear, equilateral triangle of 12 nm in diameter (top view) and a rectangle measuring 10 x 12 nm (side view). Alternatively, particles in the top view orientation exhibit a roughly circular shape 12 nm in diameter. Crossed immunoelectrophoresis revealed the presence of a major subunit type; the nature of a very minor and a third immunologically separated component remains unclear. A novel 2 x 6 arylphorin particle was detected and isolated. It comprises less than 10% of the total arylphorin material and shows a long, narrow interhexamer bridge in the electron microscope. An arylphorin dissociation intermediate identified as a trimer (1/2 x 6) was isolated; its possible quaternary structure is discussed on the basis of electron micrographs. The epitope of monoclonal antibody Ec-7 directed against tarantula (Eurypelma californicum) hemocyanin subunit d and also reactive to Calliphora arylphorin was traced to a highly conserved peptide of 27 amino acids localized in the center of the protein. The primary structure of Calliphora arylphorin as published in our preceding paper (Naumann and Scheller 1991) is compared in detail to the sequences of spider and spiny lobster hemocyanin. This revealed a basic framework of 103 strictly conserved amino acids. Isofunctional exchanges are proposed for another 76 positions. On the basis of these similarities, and the published three-dimensional model of spiny lobster hemocyanin, a detailed model of the quaternary structure of Calliphora arylphorin is presented. A second larval storage protein previously termed protein II was purified from Calliphora hemolymph. It was demonstrated to be a 500 kDa hexamer of 83 kDa subunits. In the electron microscope it shows a cubic view 9 nm in length with a large central hole and a rectangular view (9 x 10 nm) with a large central cavity. A morphologically very similar hemolymph protein was detected in Drosophila melanogaster larvae. From its structural appearance it is uncertain whether protein II belongs to the hemocyanin superfamily or not.