The chicken transferrin gene. Restriction endonuclease analysis of gene sequences in liver and oviduct DNA

Molecular, structural, and functional comparison of N lobe and C lobe of the transferrin from rock bream, Oplegnathus fasciatus, with respect to its immune response

The iron-withholding strategy of innate immunity is an effective antimicrobial defense mechanism that combats microbial infection by depriving microorganisms of Fe³⁺, which is important for their growth and propagation. Transferrins (Tfs) are a group of iron-binding proteins that exert their antimicrobial function through Fe³⁺ sequestration. The current study describes both structural and functional characteristics of a transferrin ortholog from rock bream Oplegnathus fasciatus (RbTf). The RbTf cDNA possesses an open reading frame (ORF) of 2079 bp encoding 693 amino acids. It has a molecular mass of approximately 74 kDa and an isoelectric point of 5.4. In silico analysis revealed that RbTf has two conserved domains: N-terminal domain and C-terminal domain. Pairwise homology analysis and phylogenetic analysis revealed that RbTf shared the highest identity (82.6%) with Dicentrarchus labrax Tf. According to the genomic analysis, RbTf possesses 17 exons and 16 introns, similar to the other orthologs. Here, we cloned the N terminal and C terminal domains of RbTf to evaluate their distinct functional features. Results obtained through the CAS (chrome azurol S) assay confirmed the iron-binding ability of the RbTf, and it was further determined that the iron-binding ability of rRbTfN was higher than that of rRbTfC. The antimicrobial functions of the rRbTfN and the rRbTfC were confirmed via the iron-dependent bacterial growth inhibition assay. Tissue distribution profiling revealed a ubiquitous expression with intense expression in the liver. Temporal assessment revealed that RbTf increased after stimulation of LPS, Edwardsiella tarda, and Streptococcus iniae post injection (p.i.). These findings demonstrated that RbTf is an important antimicrobial protein that can combat bacterial pathogens.

Antimicrobial effects of novel peptides cOT2 and sOT2 derived from Crocodylus siamensis and Pelodiscus sinensis ovotransferrins

In light of the increasing threat of bacterial drug resistance to human health on a global scale, research and development of antimicrobial peptides as a novel class of potent antibiotics has gained considerable attention. The present study focuses on the structural evaluation and membrane interaction of two new cationic antimicrobial peptides, cOT2 and sOT2, derived from Siamese crocodile (Crocodylus siamensis) and Chinese softshell turtle (Pelodiscus sinensis) ovotransferrins. Here, cOT1 (+3) and sOT1 (+3) were derived from reptile ovotransferrins by chromatographic purification and characterized by mass spectrometry and N-terminal sequencing analysis. In order to increase the antimicrobial efficacy, two novel peptides, cOT2 (+6) and sOT2 (+5), were designed and synthesized as "naturally-engineered" by primary amino acid sequence extension of cOT1 and sOT1, respectively. These rational designs of modified peptides were assayed in term of antimicrobial activity. These peptides display strong antimicrobial activity against several bacterial strains, e.g. Vibrio cholerae, Bacillus megaterium, and Bacillus pumilus TISTR 905, with MICs of 7-16.1μM. In terms of structural conformation in mimic environments, CD spectroscopic analysis of the secondary peptides structure features revealed fairly the similarity on α-helical content with magainin II. Hence, the modes of actions have been speculated as toroidal and carpet model. Furthermore, the disruption of intact bacterial cells induced by cOT2 and sOT2 was investigated by SEM and AFM. The results provided evidence that cOT2 and sOT2 have the potential to cause different morphological changes of bacterial cells and that these effects can be enhanced by increasing the peptide concentration.

Phylogenomic analysis of transferrin family from animals and plants

Transferrins have been identified in animals and green algae, and they consist of a family of evolutionarily related proteins that play a central role in iron transport, immunity, growth and differentiation. This study assessed the transferrin genes among 100 genomes from a wide range of animal and plant kingdoms. The results showed that putative transferrins were widespread in animals, but their gene quantity and type differ greatly between animal groups. Generally, Mammalia possess abundant transferrin genes, whereas Trematoda contain few ones. Melanotransferrin and serotransferrin are widely distributed in vertebrates, while melanotransferrin-like and transferrin-like 1 are frequent in invertebrates. However, only a few plant species detected putative transferrins, and a novel transferrin member was first uncovered in Angiospermae and Pteridophyta. The structural comparison among transferrin family members revealed seven very well-repeated and conserved characteristic motifs, despite a considerable variation in the overall sequences. The phylogenetic analysis suggested that gene duplication, gene loss and horizontal transfer contributed to the diversification of transferrin family members, and their inferred evolutionary scenario was proposed. These findings help to the understanding of transferrin distribution, characteristic motifs and residues, and evolutionary process.

Abundantly expressed hepatic genes and their differential expression in liver of prelaying and laying geese

Geese have a short egg-laying period and a low egg production rate. To induce and maintain egg laying, genes related to generating hepatic lipid for yolk deposition should be adequately expressed. Liver mRNA from 6 laying geese was extracted and used for construction of a full-length enriched cDNA library. About 2,400 clones containing gene sequences were determined and National Center for Biotechnology Information Gallus gallus Gene Index databases were used to compare and analyze these sequences. Ten highly expressed genes were selected to determine the differential expression between laying and prelay goose liver. Tissue distribution data showed that very low density apolipoprotein II, liver type fatty acid binding protein, vitellogenin I, and vitellogenin II transcripts were specifically expressed in the liver of laying geese. Ovoinhibitor, preproalbumin, alpha-2-hs-glycoprotein, and vitamin D binding protein mRNA were highly expressed in the liver and to a lesser extent in other tissues. Ovotransferrin mRNA was expressed in liver, ovary, oviduct, shell gland, brain, and adipose tissues. The concentration of transthyretin mRNA was high in the liver and brain. The mRNA concentrations of liver type fatty acid binding protein, alpha-2-hs-glycoprotein, and transthyretin in the livers of laying and prelay geese were not different. The concentrations of hepatic ovotransferrin, ovoinhibitor, preproalbumin, very low density apolipoprotein II, vitellogenin I, vitellogenin II, and vitamin D binding protein mRNA were higher in the liver of laying geese than in prelay geese, suggesting that these genes may be involved in laying function or lipid metabolism related to egg formation.

Differential regulation of transferrin 1 and 2 in Aedes aegypti

Available evidence has shown that transferrins are involved in iron metabolism, immunity and development in eukaryotic organisms including insects. Here we characterize the gene and message expression profile of Aedes aegypti transferrin 2 (AaTf2) in response to iron, bacterial challenge and life stage. We show that AaTf2 shares a low similarity with A. aegypti transferrin 1 (AaTf1), but higher similarity with mammalian transferrins and avian ovotransferrin. Iron-binding pocket analysis indicates that AaTf2 has residue substitutions of Y188F, T120S, and R124S in the N lobe, and Y517N, H585N, T452S, and R456T in the C lobe, which could alter or reduce iron-binding activity. In vivo studies of message expression reveal that AaTf2 message is expressed at higher levels in larva and pupa, as well as adult female ovaries 72h post blood meal (PBM) and support that AaTf2 could play a role in larval and pupal development and in late physiological events of the gonotrophic cycle. Bacterial challenge significantly increases AaTf1 expression in ovaries at 0 and 24h PBM, but decreases AaTf2 expression in ovaries at 72h PBM, suggesting that AaTf1 and AaTf2 play different roles in immunity of female adults during a gonotrophic cycle.

Isolation, cloning and sequencing of transferrins from red-eared turtle, African ostrich, and turkey

Transferrins form an important class of iron-binding proteins widely distributed in the physiological fluids of vertebrates and invertebrates. In vertebrates they are present mostly in serum as serotransferrins. In birds and reptiles transferrins are also found in eggs as ovotransferrins. However, until now only chicken and duck ovotransferrin sequences have been published. This paper presents data on the purification, biochemical analysis, cloning and sequencing of ovotransferrins from red-eared turtle, African ostrich and turkey, revealing their significant homology with other known ovotransferrin sequences. The proteins were purified by size-exclusion and anion-exchange chromatography. Isoelectric points, iron-saturated and iron-free spectra, as well as the mRNA nucleotide sequences of 2,409 nt (ORF: 2,106 nt encoding a 701-amino-acid polypeptide; ), 2,418 nt (ORF 2,118 nt encoding a 705-amino-acid polypeptide; ), and 2,397 nt (ORF: 2,118 nt encoding a 705-amino-acid polypeptide; ) were determined for ostrich (OtrF), red-eared turtle (TtrF), and turkey (MtrF) ovotransferrin, respectively.

Evolution of the transferrin family: Conservation of residues associated with iron and anion binding

The transferrin family spans both vertebrates and invertebrates. It includes serum transferrin, ovotransferrin, lactoferrin, melanotransferrin, inhibitor of carbonic anhydrase, saxiphilin, the major yolk protein in sea urchins, the crayfish protein, pacifastin, and a protein from green algae. Most (but not all) contain two domains of around 340 residues, thought to have evolved from an ancient duplication event. For serum transferrin, ovotransferrin and lactoferrin each of the duplicated lobes binds one atom of Fe (III) and one carbonate anion. With a few notable exceptions each iron atom is coordinated to four conserved amino acid residues: an aspartic acid, two tyrosines, and a histidine, while anion binding is associated with an arginine and a threonine in close proximity. These six residues in each lobe were examined for their evolutionary conservation in the homologous N- and C-lobes of 82 complete transferrin sequences from 61 different species. Of the ligands in the N-lobe, the histidine ligand shows the most variability in sequence. Also, of note, four of the twelve insect transferrins have glutamic acid substituted for aspartic acid in the N-lobe (as seen in the bacterial ferric binding proteins). In addition, there is a wide spread substitution of lysine for the anion binding arginine in the N-lobe in many organisms including all of the fish, the sea squirt and many of the unusual family members i.e., saxiphilin and the green alga protein. It is hoped that this short analysis will provide the impetus to establish the true function of some of the TF family members that clearly lack the ability to bind iron in one or both lobes and additionally clarify the evolutionary history of this important family of proteins.

Identification of a distinct antibacterial domain within the N-lobe of ovotransferrin

We have evaluated the bactericidal activity of hen ovotransferrin (OTf), which was found to operate regardless of its iron-deprivation properties, with the objective of isolating the bactericidal domain. The amino-terminal half-molecule (N-lobe, residues 1-332) of OTf, isolated by trypsin-nicking, retained the bactericidal activity independently of iron-deprivation, but not the carboxyl-terminal half-molecule (C-lobe, residue 342-686), suggesting the presence of a bactericidal domain within the N-lobe of the molecule. Specific cleavage at the aspartyl residues of OTf, by diluted-acid procedure, yielded fairly large peptides, whereas proteolysis for 150 min produced the strongest bactericidal peptides mixture. The bactericidal domain was purified from the active hydrolysate by gel filtration and reversed-phase HPLC and showed activity against S. aureus as well as E. coli K-12. Electrophoretic analysis on tricine-SDS-PAGE revealed a bactericidal peptide with an average M(r) of 9900 Da under non-reducing conditions. In combination with the specificity of cleavage (Asp-X) and the molecular mass, its N-terminal microsequencing corresponded to a cationic peptide consisting of 92 residues located within the 109-200 sequence of the N-lobe of OTf, containing three intrachain disulfide bridges, featuring a common structural motif occurs in the N-lobes of transferrins for which the sequence is available. Two of the disulfides (C160-C174 and C171-C182) form surface exposed cringle bridges lying on the opposite side of the iron-binding site from the interdomain cleft and showing marked sequence homology to insect defensins, which are blockers of the voltage-dependent K+ channels. The peptide lost antibacterial activity when its disulfide bonds were reduced, indicating the importance of its tertiary structure for the exertion of antibiotic activity.

A proteinase inhibitor from egg yolk of hen is an ovoinhibitor analog

A proteinase inhibitor, tentatively termed vitelloinhibitor, was purified from yolk of hen's ovarian follicles. It resembled egg-white ovoinhibitor not only in inhibitory spectrum (active for bovine trypsin and bovine chymotrypsin) but also in thermal stability, pH stability, antiserum reactivity and amino-acid composition. However, vitelloinhibitor had different molecular weight from that of ovoinhibitor. An alpha 2-proteinase inhibitor preparation, isolated from laying hen's serum in the present study, was found to exhibit two bands, and the larger one of the latter corresponded to vitelloinhibitor in molecular weight. The partial N-terminal amino-acid sequence of vitelloinhibitor was the same as those of the two components of serum inhibitor and all three agreed with that of ovoinhibitor. Vitelloinhibitor is likely to be an ovoinhibitor analog derived from a serum precursor, which might be the larger component of alpha 2-proteinase inhibitor.

Comparative study of the primary structures of sero-, lacto- and ovotransferrin glycans from different species

In order to establish relationships between glycan structure and biological activity and to answer the question: Are glycans markers of evolution?, the authors undertook a comparative study of the glycan primary structures of different transferrins (sero-, lacto- and ovotransferrins) from several species. By associating permethylation--mass spectrometry and 1H NMR spectroscopy, the primary structure of the following transferrin glycans were determined: human, bovine, hen, horse, marsupial, mouse, rabbit, rat and sheep serotransferrins; human, mouse, bovine and goat lactotransferrins; hen and turkey ovotransferrins. The results obtained led to the conclusion that transferrin glycans are specific for each transferrin and, for a given transferrin, specific to the species. No relationship could be established a priori between primary structure and function of transferrin glycans.

Structural basis for restriction-site polymorphism at the albumin locus in inbred strains of rats

Two types of variant EcoRI restriction enzyme patterns of albumin-gene DNA fragments are found in different inbred strains of rats and reflect allelic polymorphism. The structural basis of the two allelic forms has been analyzed by mapping the EcoRI fragments using cloned albumin cDNA probes corresponding to the 5' or 3' end of the rat albumin mRNA and different genomic subclones. Additional restriction fragment length polymorphism has been detected using the restriction endonucleases HindIII and MspI. The results suggest that the two allelic variants differ from each other by multiple cleavage-site variations (base-pair substitutions) and by an insertion or deletion of DNA sequences. An extensive DNA sequence variation appears to exist between the two forms of the albumin gene; we have estimated that as much as 4% of the nucleotides in this region varied between the two alleles. All of this genetic variation is found in the intervening sequences of the gene and has no phenotypic manifestation.

Structural variants of the alpha-fetoprotein gene in different inbred strains of rat

Two structural variants of the rat alpha-fetoprotein (AFP) gene have been detected in different inbred strains of rats by EcoRI or HindIII restriction enzyme cleavage of cellular DNA, agarose gel electrophoresis and Southern blot hybridization using 32P-labeled cloned rat AFP cDNA probes. The type I AFP gene variant is characteristic of the Sprague-Dawley strain, and type II is found in Buffalo rats. These variants appear to represent two different allelic forms of the rat AFP gene since they are inherited in a normal Mendelian fashion when Sprague-Dawley and Buffalo rats are crossed. The mapping results suggest that the two allelic variants differ from each other by multiple cleavage site variations (base pair substitutions) and by an insertion or deletion of DNA sequences. An extensive sequence variation appears to exist between the two forms of the rat AFP gene; we have estimated that as much as 2.7% of the nucleotides in this region vary between the two alleles.

Developmental regulation of globin and nonglobin messenger RNAs in avian erythroid cells

During embryonic development in the chicken two morphologically distinct erythroid cell populations sequentially appear. Coincidentally with the change in cell populations that begins on the sixth day of embryonic life, the hemoglobins of the early embryo are gradually replaced by a new set of hemoglobins, which are almost identical to those of the adult chicken. We have used recombinant DNAs to investigate the molecular mechanisms underlying these developmental changes. With respect to the eight nonglobin species of messenger RNA that we have studied, seven are present at approximately equal concentrations in erythroid cells from 5-day embryos and from anemic adults. This suggests that the replacement of erythroid cell populations is not accompanied by a general reorganization of gene expression. With respect to globin gene expression, however, we find that all but one of the globin genes studied (alpha D-globin) undergo dramatic developmental regulation. We have also shown that the expression of the gene for the embryo specific alpha-like globin, pi'-globin, is principally regulated at the level of transcription.

Estimation of the neutral mutation rate in a finite population from DNA sequence data

The sampling theory for the infinite site model taking into account the phylogenetic relationship between the alleles is developed for those cases in which two or three alleles are observed in the sample. From this theory a maximum likelihood estimate of theta = 4N mu can be obtained. Unlike the maximum likelihood estimate of theta based on the infinite allele model or the number of segregating sites, this estimate of theta is a function of the frequencies of the alleles. This method is used to estimate theta for mitochondrial DNA in Drosophila melanogaster and D. virilis from data obtained by Shah and Langley (1979. Nature (London) 281, 696-699) using restriction endonucleases.

The complete nucleotide sequence of the chicken ovotransferrin mRNA

The nucleotide sequence of an almost double-stranded cDNA copy [Cochet, M., Perrin, F., Gannon, F., Krust, A., Chambon, P., McKnight, G. S., Lee, D. C., Mayo, K. E., and Palmiter, R. D. (1979) Nucleic Acids Res. 6, 2435-2452] of chicken ovotransferrin (conalbumin) mRNA has been determined. Taking into account the previously reported 5'-end sequence [Cochet, M., Gannon, F., Hen, R., Maroteaux, L., Perrin, F., and Chambon, P. (1979) Nature (Lond.) 282, 567-574] we present the complete nucleotide sequence of the ovotransferrin mRNA from which the amino acid sequence of the protein is inferred. A computer and statistical analysis of the nucleotide sequence reveals a pattern of internal homology which confirms that the present-day chicken ovotransferrin gene (and by extrapolation the transferrin genes of other species) has evolved by duplication and gives some support to the quadruplication hypothesis of transferrin evolution.