Isolation and properties of vitellogenic ferritin from snails

Yolk proteins of the schistosomiasis vector snail Biomphalaria glabrata revealed by multi-omics analysis

Vitellogenesis is the most important process in animal reproduction, in which yolk proteins play a vital role. Among multiple yolk protein precursors, vitellogenin (Vtg) is a well-known major yolk protein (MYP) in most oviparous animals. However, the nature of MYP in the freshwater gastropod snail Biomphalaria glabrata remains elusive. In the current study, we applied bioinformatics, tissue-specific transcriptomics, ovotestis-targeted proteomics, and phylogenetics to investigate the large lipid transfer protein (LLTP) superfamily and ferritin-like family in B. glabrata. Four members of LLTP superfamily (BgVtg1, BgVtg2, BgApo1, and BgApo2), one yolk ferritin (Bg yolk ferritin), and four soma ferritins (Bg ferritin 1, 2, 3, and 4) were identified in B. glabrata genome. The proteomic analysis demonstrated that, among the putative yolk proteins, BgVtg1 was the yolk protein appearing in the highest amount in the ovotestis, followed by Bg yolk ferritin. RNAseq profile showed that the leading synthesis sites of BgVtg1 and Bg yolk ferritin are in the ovotestis (presumably follicle cells) and digestive gland, respectively. Phylogenetic analysis indicated that BgVtg1 is well clustered with Vtgs of other vertebrates and invertebrates. We conclude that, vitellogenin (BgVtg1), not yolk ferritin (Bg yolk ferritin), is the major yolk protein precursor in the schistosomiasis vector snail B. glabrata.

Dormancy in Embryos: Insight from Hydrated Encysted Embryos of an Aquatic Invertebrate

Numerous aquatic invertebrates remain dormant for decades in a hydrated state as encysted embryos. In search for functional pathways associated with this form of dormancy, we used label-free quantitative proteomics to compare the proteomes of hydrated encysted dormant embryos (resting eggs; RE) with nondormant embryos (amictic eggs; AM) of the rotifer Brachionus plicatilisA total of 2631 proteins were identified in rotifer eggs. About 62% proteins showed higher abundance in AM relative to RE (Fold Change>3; p = 0.05). Proteins belonging to numerous putative functional pathways showed dramatic changes during dormancy. Most striking were changes in the mitochondria indicating an impeded metabolism. A comparison between the abundance of proteins and their corresponding transcript levels, revealed higher concordance for RE than for AM. Surprisingly, numerous highly abundant dormancy related proteins show corresponding high mRNA levels in metabolically inactive RE. As these mRNAs and proteins degrade at the time of exit from dormancy they may serve as a source of nucleotides and amino acids during the exit from dormancy. Because proteome analyses point to a similarity in functional pathways of hydrated RE and desiccated life forms, REs were dried. Similar hatching and reproductive rates were found for wet and dried REs, suggesting analogous pathways for long-term survival in wet or dry forms. Analysis by KEGG pathways revealed a few general strategies for dormancy, proposing an explanation for the low transcriptional similarity among dormancies across species, despite the resemblance in physiological phenotypes.

Iron and nitrosative metabolism in the Antarctic mollusc Laternula elliptica

The objective of this work was to study Fe distribution, and oxidative and nitrosative metabolism in Laternula elliptica for physiological analysis and interspecific comparisons. Lipid peroxidation, superoxide dismutase and catalase activity and total Fe content were estimated in the digestive glands (DG) of L. elliptica. The labile Fe pool (LIP) represents the amount of cellular Fe responsible for catalyzing radical-dependent reactions. LIP assessed by the calcein assay, represents 3.5% of the total Fe in L. elliptica. Experimental isolation of ferritin (Ft) was performed. Subunit analyses of the protein by SDS-polyacrilamide gel electrophoresis indicated that the protein was composed of 20.6kDa protein subunits, consistent with the horse spleen Ft and the molecular weight markers, however, a higher molecular mass subunit could appear. The identity of the protein was confirmed by Western blot analysis. The nitrate+nitrite content was 73±7pmol/mg fresh mass (FW). The nitric oxide (NO) content in DG homogenates, assessed by electronic paramagnetic resonance (EPR) spin trapping measurements using the NO trap sodium-N-methyl-D-glucamine dithiocarbamate-Fe at room temperature, was 30±2pmol/mg FW. Nitric oxide synthase-like activity (1.50±0.09pmol/mg FW min) was assessed by measuring NO production by EPR in the presence of L-arginine (L-A) and NADPH. This activity was significantly inhibited by L-A analogs such as Nω-nitro-L-arginine methyl ester hydrochloride (-77%) and Nω-nitro-L-arginine (-62%), or by the lack of added L-A (-55%). The data presented here documented the physiological presence of labile Fe, Ft and highly reactive nitrogen species, and are the first evidence that support the hypothesis that NO being generated in L. elliptica might contribute to restrict oxidative damage by a close link with Fe metabolism.

Fate of blood meal iron in mosquitoes

Iron is an essential element of living cells and organisms as a component of numerous metabolic pathways. Hemoglobin and ferric-transferrin in vertebrate host blood are the two major iron sources for female mosquitoes. We used inductively coupled plasma mass spectrometry (ICP-MS) and radioisotope labeling to quantify the fate of iron supplied from hemoglobin or as transferrin in Aedes aegypti. At the end of the first gonotrophic cycle, approximately 87% of the ingested total meal heme iron was excreted, while 7% was distributed into the eggs and 6% was stored in different tissues. In contrast, approximately 8% of the iron provided as transferrin was excreted and of that absorbed, 77% was allocated to the eggs and 15% distributed in the tissues. Further analyses indicate that of the iron supplied in a blood meal, approximately 7% appears in the eggs and of this iron 98% is from hemoglobin and 2% from ferric-transferrin. Whereas, of iron from a blood meal retained in body of the female, approximately 97% is from heme and <1% is from transferrin. Evaluation of iron-binding proteins in hemolymph and egg following intake of (59)Fe-transferrin revealed that ferritin is iron loaded in these animals, and indicate that this protein plays a critical role in meal iron transport and iron storage in eggs in A. aegypti.

Paragonimus westermani: molecular cloning, expression, and characterization of a recombinant yolk ferritin

Ferritin is an intracellular protein involved in iron metabolism. A cDNA PwYF-1 cloned from the adult Paragonimus westermani cDNA library encoded a putative polypeptide of 216 amino acids homologous with ferritins of vertebrates and invertebrates. Febinding motifs identified in PwYF-1 polypeptide were conserved and predicted to form a ferroxidase center. PwYF-1 polypeptide contained an extended peptide of 45 amino acids at its C-terminus. Recombinant PwYF-1 protein, expressed and purified from Escherichia coli, showed iron-uptake ability and ferroxidase activity. Ferroxidase activity of recombinant PwYF-1 protein was reactivated by secondary addition of apotransferrin to assay mixture. Mouse immune serum raised against the recombinant PwYF-1 protein recognized specifically 24 kDa protein from adult P. westermani lysate. PwYF-1 protein was localized to vitelline follicles and the eggs of P. westermani. Collectively, PwYF-1 protein was identified as a P. westermani yolk ferritin.

Isolation and characterization of mosquito ferritin and cloning of a cDNA that encodes one subunit

Ferritin, an iron storage protein, was isolated from larvae and pupae of Aedes aegypti grown in an iron-rich medium. Mosquito ferritin is a high molecular weight protein composed of several different, relatively small, subunits. Subunits of molecular mass 24, 26, and 28 kDa are equally abundant, while that of 30 kDa is present only in small amounts. The N-terminal sequence of the 24 and 26 kDa subunits are identical for the first 30 amino acids, while that of the 28 kDa subunit differs. Studies using antiserum raised against a subunit mixture showed that the ferritin subunit were present in larvae, pupae, and adult females, and were increased in animals exposed to excess iron. The antiserum also was used to screen a cDNA library from unfed adult female mosquitoes. Nine clones were obtained that differed only in a 27 bp insertion in the 3' end. Rapid amplification of cDNA ends (RACE) was used to obtain the complete protein coding sequence. A putative iron-responsive element (IRE) is present in the 5'-untranslated region. The deduced amino acid sequence shows a typical leader sequence, consistent with the fact that most insect ferritins are secreted, rather than cytoplasmic proteins. The sequence encodes a mature polypeptide of 20,566 molecular weight, smaller than the estimated size of any of the subunits. However, the sequence exactly matches the N-terminal sequences of the 24 and 26 kDa subunits as determined by Edman degradation. Of the known ferritin sequences, that of the mosquito is most similar to that of somatic cells of a snail.

cDNA cloning and deduced amino acid sequence of two ferritins: soma ferritin and yolk ferritin, from the snail Lymnaea stagnalis L

Pulmonate freshwater snails contain two different ferritin types, soma ferritin and yolk ferritin. A cDNA library was constructed from midgut gland poly(A)-rich RNA of the snail Lymnaea stagnalis L. and recombinant clones encoding both ferritin types were obtained by immunoscreening. The longest cDNA inserts had a length of 859 bp (soma ferritin) and 1548 bp (yolk ferritin) and the specificity of these inserts was confirmed by immunoprecipitation of both ferritin types translated in vitro from hybrid-selected mRNAs. The 5' untranslated region (UTR) of the soma ferritin mRNA contains a 28-bp element which shows 64% sequence identity with the iron-responsive element (IRE) of vertebrate ferritin mRNAs. The soma ferritin mRNA is strongly translated in the wheat germ system but poorly translated in rabbit reticulocyte lysate. The yolk ferritin mRNA, which contains no IRE, is equally well translated in both in vitro translation systems. The deduced amino acid sequence of the soma ferritin subunit (174 amino acid residues, M(r) 20140) shows 50-70% sequence identity with subunits of vertebrate ferritins. After removal of an 18-amino-acid-residue signal sequence the deduced protein sequence of yolk ferritin contains 221 amino acids (M(r) 25438). Sequence identity of this chain with other eukaryotic ferritin chains is only 31-42%. Both snail ferritin sequences are more similar to the H-subunit type of vertebrate ferritins than to the L-type and both have the H-specific amino acid residues of the ferroxidase centre. The yolk ferritin sequence has a 42-amino-acid-residue insertion predicted to reside in the L loop of the subunit.

Ovohemerythrin, a major 14-kDa yolk protein distinct from vitellogenin in leech

A 14-kDa protein was identified as a major component of mature oocytes of the leech Theromyzon tessulatum. This protein was, like vitellin, detected in the content of yolk granules and was purified by gel-permeation and ion-exchange chromatography. The yolk protein corresponded to an iron-binding protein which exists in a monomeric unglycosylated form and had no similarities to vitellin. However, a strong resemblance between this protein and sipunculid hemerythrin, a non-heme iron-binding protein, was observed on the basis of its characteristics including molecular mass, iron content, ultraviolet/visible spectrum, amino acid composition and N-terminal sequence. These similarities with hemerythrin and the accumulation of the protein in the oocyte justify the name ovohemerythrin given to the molecule. A coelomic-fluid protein immunologically related to ovohemerythrin was detected in vitellogenic animals. The protein was purified with the chromatographic procedure used to isolate ovohemerythrin from oocytes and was found to be similar to the oocyte protein. This circulating ovohemerythrin was present in large amounts in the coelomic fluid while gametogenesis is in progress, i.e. after the third and last blood meal of the animal (stage 3), except at the time of oocyte enlargement when its concentration decreases dramatically. However, in contrast to vitellogenin, which is detected specifically in the coelomic fluid of leeches at stage 3, circulating ovohemerythrin is also observed after the first (stage 1) and second (stage 2) blood meal. This observation suggests a more complex function for ovohemerythrin than being merely a yolk nutrient for the embryo.

Molecular size heterogeneity of ferritin in mouse liver

As much as 4% of the total protein in pure liver ferritin from mice with short-term parenteral iron overload produces a minor band migrating anodally to the major (alpha) band of holoferritin with non-denaturing polyacrylamide gel electrophoresis. The components in this minor band and the alpha band have been isolated to purity by preparative electrophoretic fractionation. The protein in the minor band is ferritin, since it contains ferric iron and fulfills defining criteria at the level of biochemistry, immunology and ultrastructure. Native polyacrylamide electrophoresis with pore-size-gradient gels shows that the ferritin molecules in the minor band have a slightly smaller diameter than the holoferritin in the alpha band. Isoelectric focusing reveals that the smaller ferritin has an identical number and range of charge isomers (pI 4.9-5.3) as the larger ferritin, but the relative amount of each size class within some isoferritin bands differs. The smaller ferritin molecules are structurally intact and are made from polypeptide subunits with Mr 18 000; the larger ferritin molecules have subunits with Mr 22 000. The minor species of hepatic ferritin thus has a smaller molecular size because it is made mainly from smaller subunits. No minor electrophoretic band can be detected in liver ferritin obtained from mice with normal iron levels. These results demonstrate that siderosis induces the formation of molecular size polymorphism (macroheterogeneity) in mouse liver ferritin. The new smaller hepatic ferritin could serve to redistribute excess iron into the main storage organs during the early response to iron overload, since it appears to be identical to one of the two types of serum ferritin molecules present in these siderotic mice.