Biotin-binding proteins and biotin transport to oocytes

A Tar aspartate receptor and Rubisco-like protein substitute biotin in the growth of rhizobial strains

Biotin is a key cofactor of metabolic carboxylases, although many rhizobial strains are biotin auxotrophs. When some of these strains were serially subcultured in minimal medium, they showed diminished growth and increased excretion of metabolites. The addition of biotin, or genetic complementation with biotin synthesis genes resulted in full growth of Rhizobium etli CFN42 and Rhizobium phaseoli CIAT652 strains. Half of rhizobial genomes did not show genes for biotin biosynthesis, but three-quarters had genes for biotin transport. Some strains had genes for an avidin homologue (rhizavidin), a protein with high affinity for biotin but an unknown role in bacteria. A CFN42-derived rhizavidin mutant showed a sharper growth decrease in subcultures, revealing a role in biotin storage. In the search of biotin-independent growth of subcultures, CFN42 and CIAT652 strains with excess aeration showed optimal growth, as they also did, unexpectedly, with the addition of aspartic acid analogues α- and N-methyl aspartate. Aspartate analogues can be sensed by the chemotaxis aspartate receptor Tar. A tar homologue was identified and its mutants showed no growth recovery with aspartate analogues, indicating requirement of the Tar receptor in such a phenotype. Additionally, tar mutants did not recover full growth with excess aeration. A Rubisco-like protein was found to be necessary for growth as the corresponding mutants showed no recovery either with high aeration or aspartate analogues; also, diminished carboxylation was observed. Taken together, our results indicate a route of biotin-independent growth in rhizobial strains that included oxygen, a Tar receptor and a previously uncharacterized Rubisco-like protein.

Modulation of folliculogenesis in adult laying chickens by bisphenol A and bisphenol S: Perspectives on ovarian morphology and gene expression

Both bisphenol A (BPA) and its analog bisphenol S (BPS) are industrial chemicals that have been used to make certain plastic products applied in chicken farms, including food and water containers. They are endocrine disrupting chemicals (EDCs) with xenoestrogenic activities and affect reproductive success in many ways. It was hypothesized that BPA and BPS could adversely affect the folliculogenesis in chickens due to their disruption of the estrogen responses, using either genomic or non-genomic mechanisms. This study investigated the deleterious effects of BPA and BPS on the ovaries when adult layer chickens were orally treated with these EDCs at 50 μg/kg body weight, the reference dose for chronic oral exposure of BPA established by the U.S. EPA. The chickens in both BPA and BPS-treated groups showed a decreased number of the preovulatory follicles. BPA-treated chickens showed a significant decrease in the diameter of F1. Additionally, both BPA and BPS treatments increased the infiltrations of lymphocytes and plasma cells in ovaries. Moreover, it was found that the ovaries of BPS-treated chickens weighed the most among the groups. RNA sequencing and subsequent pathway enrichment analysis of differentially expressed genes revealed that both BPA- and BPS-treatment groups showed significant changes in gene expression and pathways related to reproduction, immune function and carcinogenesis. Taken together, both BPA and BPS are potentially carcinogenic and have deleterious effects on the fertility of laying chickens by inducing inflammation, suggesting that BPS may not be a safe replacement for BPA.

Zebavidin--an avidin-like protein from zebrafish

The avidin protein family members are well known for their high affinity towards D-biotin and high structural stability. These properties make avidins valuable tools for a wide range of biotechnology applications. We have identified a new member of the avidin family in the zebrafish (Danio rerio) genome, hereafter called zebavidin. The protein is highly expressed in the gonads of both male and female zebrafish and in the gills of male fish, but our data suggest that zebavidin is not crucial for the developing embryo. Biophysical and structural characterisation of zebavidin revealed distinct properties not found in any previously characterised avidins. Gel filtration chromatography and native mass spectrometry suggest that the protein forms dimers in the absence of biotin at low ionic strength, but assembles into tetramers upon binding biotin. Ligand binding was analysed using radioactive and fluorescently labelled biotin and isothermal titration calorimetry. Moreover, the crystal structure of zebavidin in complex with biotin was solved at 2.4 Å resolution and unveiled unique ligand binding and subunit interface architectures; the atomic-level details support our physicochemical observations.

Maternal investment and nutrient use affect phenotype of American alligator and domestic chicken hatchlings

Maternal investment by oviparous amniotes, in the form of yolk and albumen, and the mechanisms by which embryos use available energy and nutrients have a profound effect on embryo and, consequently, hatchling phenotype. Nutrient provisioning and uptake vary within and among oviparous taxa, avian and non-avian reptiles, due to differences and similarities in environment, behavior, and phylogeny. Eggs of crocodilians, the closest extant relatives to modern birds, are ideal models for examining modes of embryonic development, especially with regard to nutrient uptake, in non-avian reptiles and comparing them with those of birds. In this study, we investigated egg composition, embryo growth, and nutrient use in the domestic chicken (Gallus gallus) and American alligator (Alligator mississippiensis). We explored egg composition by separating and weighing components of fresh eggs. We measured embryo growth and nutrient usage by dissecting embryos and by obtaining samples of liquid from the amnion, digestive tract, and yolk sac throughout the last half of incubation. Variation in albumen mass contributed most to egg mass variation in chicken eggs, whereas alligator eggs were composed almost equally of yolk and albumen, although larger eggs contained proportionally more albumen and less yolk than smaller eggs. Both chicken and alligator albumen were mostly water (87% and 96%, respectively) although chicken albumen contained over three times more solid mass per gram than alligator albumen. In both species, yolk contained a high proportion of solids. Larger eggs produced larger hatchlings in both chickens and alligators, but albumen solids contributed to embryo mass only in chicken embryos. However, intact albumen proteins appeared in the stomach in embryos of both species. While the final disposition of albumen in alligators is unclear, variation in maternal investment of yolk at oviposition was responsible for nearly all of the variation in alligator hatchling phenotype, while both yolk and albumen contributed to chicken hatchling mass.

Preliminary studies on the selective accumulation of vitamin-targeted polymers within tumors

Many different cancer types have previously been found to show increased uptake of the vitamins folate, vitamin B12, and biotin; however, it is not known whether these tumor lines show increased uptake of one or more of the vitamins. The current study was designed to examine the relative uptake of the three vitamins in 10 different types of cell lines. Rhodamine-labeled hydroxypropyl-methacrylamide (HPMA) was targeted with vitamin B(12), folate, or biotin, and the uptake of the labeled polymer was compared both in in vitro cell cultures and in mice-bearing tumors from a variety of tumor cell lines. Fluorescent microscopy of cell cultures and histological examination of tumor sections showed greatly increased uptake of the fluorescently labeled polymer in many tumors when the polymer was targeted with folate, biotin, or vitamin B(12). Tumors with enhanced uptake of vitamin B(12)- or folate-targeted rhodamine-HPMA also showed increased uptake of biotin-Rho-HPMA. In contrast, tumors with increased uptake of folate-Rho-HPMA did not show increased uptake of vitamin B12 (VB(12))-HPMA and vice versa. These findings suggest that vitamin-targeted polymers may greatly increase the uptake of drug-polymer complexes in certain tumors, which may result in an increased efficacy of antitumor agents, and which may allow for easier imaging of both the primary and metastatic tumors.

Structure and characterization of a novel chicken biotin-binding protein A (BBP-A)

Background

The chicken genome contains a BBP-A gene showing similar characteristics to avidin family genes. In a previous study we reported that the BBP-A gene may encode a biotin-binding protein due to the high sequence similarity with chicken avidin, especially at regions encoding residues known to be located at the ligand-binding site of avidin.

Results

Here, we expand the repertoire of known macromolecular biotin binders by reporting a novel biotin-binding protein A (BBP-A) from chicken. The BBP-A recombinant protein was expressed using two different expression systems and purified with affinity chromatography, biochemically characterized and two X-ray structures were solved – in complex with D-biotin (BTN) and in complex with D-biotin D-sulfoxide (BSO). The BBP-A protein binds free biotin with high, "streptavidin-like" affinity (K_d ~ 10^-13 M), which is about 50 times lower than that of chicken avidin. Surprisingly, the affinity of BBP-A for BSO is even higher than the affinity for BTN. Furthermore, the solved structures of the BBP-A – BTN and BBP-A – BSO complexes, which share the fold with the members of the avidin and lipocalin protein families, are extremely similar to each other.

Conclusion

BBP-A is an avidin-like protein having a β-barrel fold and high affinity towards BTN. However, BBP-A differs from the other known members of the avidin protein family in thermal stability and immunological properties. BBP-A also has a unique ligand-binding property, the ability to bind BTN and BSO at comparable affinities. BBP-A may have use as a novel material in, e.g. modern bio(nano)technological applications.

Chicken genome analysis reveals novel genes encoding biotin-binding proteins related to avidin family

BACKGROUND

A chicken egg contains several biotin-binding proteins (BBPs), whose complete DNA and amino acid sequences are not known. In order to identify and characterise these genes and proteins we studied chicken cDNAs and genes available in the NCBI database and chicken genome database using the reported N-terminal amino acid sequences of chicken egg-yolk BBPs as search strings.

RESULTS

Two separate hits showing significant homology for these N-terminal sequences were discovered. For one of these hits, the chromosomal location in the immediate proximity of the avidin gene family was found. Both of these hits encode proteins having high sequence similarity with avidin suggesting that chicken BBPs are paralogous to avidin family. In particular, almost all residues corresponding to biotin binding in avidin are conserved in these putative BBP proteins. One of the found DNA sequences, however, seems to encode a carboxy-terminal extension not present in avidin.

CONCLUSION

We describe here the predicted properties of the putative BBP genes and proteins. Our present observations link BBP genes together with avidin gene family and shed more light on the genetic arrangement and variability of this family. In addition, comparative modelling revealed the potential structural elements important for the functional and structural properties of the putative BBP proteins.

Serial analysis of gene expression in turkey sperm storage tubules in the presence and absence of resident sperm

Turkey sperm lose viability within 8-18 h when stored as liquid semen using current methods and extenders. In contrast, turkey hens maintain viable, fertile sperm in their sperm storage tubules (SST) for 45 or more days following a single insemination. Our long-term objectives are to identify and characterize differentially expressed genes that may underlie this prolonged sperm storage and then use this information to develop improved methods for storing liquid turkey semen. We employed serial analysis of gene expression (SAGE) to compare gene expression patterns in turkey SST recovered from hens after artificial insemination (AI) with extended semen (sperm AI) or extender alone (control AI). We constructed two separate SAGE libraries with SST RNA obtained from sperm and control AI hens. We used these libraries to generate 95,325 ten-base pair SAGE tags. These 95,325 tags represented 27,430 unique genes. The sperm and control AI libraries contained 47,663 and 47,662 tags representing 18,030 and 19,101 putative unique transcripts, respectively. Approximately 1% of these putative unique genes were differentially expressed (P<0.05) between treatments. Tentative annotations were ascribed to the SAGE tag nucleotide sequences by comparing them against publicly available SAGE tag and cDNA sequence databases. Based on its SAGE tag nucleotide sequence, we cloned a partial turkey avidin cDNA and confirmed its up-regulation in the sperm AI SST. The bioinformatics and experimental procedures employed to clone turkey avidin and confirm its differential expression represent a useful paradigm for analyzing SAGE tag data from relatively uncharacterized model systems.

An oocytic membrane receptor for biotin-binding protein

The chicken oocyte accumulates a biotin-binding protein (BBP) in the yolk that is distinct from the avidin in the 'egg white'. An identical BBP to that of the yolk is also present in the circulation of the laying hen. We report the first evidence for the existence of a BBP receptor in the oocyte vitelline membrane. Reduction of the 100 kDa receptor results in loss of BBP-binding activity; this suggests that a disulfide bonded region of the receptor is necessary for maintaining BBP-binding activity. We show further that the levels of serum BBP are strictly dependent on the presence of estrogen. As expected, BBP is not detected in significant quantities in rooster serum. Thus, these results suggest that circulatory BBP, like other estrogen-dependent components of serum, has a cognate binding activity on the oocyte membrane that may mediate its endocytosis.

Simultaneous purification of biotin-binding proteins-I and -II from chicken egg yolk and their characterization

Chicken egg yolk biotin-binding protein-I (BBP-I) has been purified to homogeneity along with the tetrameric BBP-II by a common protocol. The purification includes delipidation of egg yolk by butanol extraction, DEAE-Sephacel chromatography, treatment with guanidinium chloride and biotin-aminohexyl-Sepharose affinity chromatography. The identity of purified BBP-I was ascertained by its physicochemical properties as well as by its immunological cross-reactivity and precursor-product relationship with BBP-II.

Separation and characterization of the two Asn-linked glycosylation sites of chicken serum riboflavin-binding protein. Glycosylation differences despite similarity of primary structure

Serum riboflavin-binding protein, a phosphoglycoprotein from the blood of laying hens, contains two Asn-Xaa-(Thr)Ser sequons in very similar but well-separated regions of amino acid sequence. In order to evaluate the effect of local amino acid sequence on the structure of the attached oligosaccharides, serum riboflavin-binding protein was purified to homogeneity, reduced and alkylated, digested with trypsin, and the two glycopeptides were separated by reversed-phase chromatography. After digestion with peptide-N-glycosidase F the released oligosaccharides were separated by high-pH anion-exchange chromatography and the oligosaccharide profiles of the two glycopeptides were compared. Although the two asparagine residues that are glycosylated are contained in pentapeptide segments in which four out of five amino acids are identical, the array of oligosaccharides present at each site show differences in both type and distribution. This suggests that local secondary or tertiary structure, or the order of glycosylation, influences the oligosaccharide structure more than does the primary structure flanking the attachment site.

Purification and characterization of biotin-binding protein II from chicken oocytes

BBP-II, the major biotin-binding protein from chicken oocytes, was purified 12,000-fold with a 22% yield. The purification procedure includes butan-1-ol extraction of yolk lipids, phosphocellulose chromatography of the water-soluble proteins, DEAE-cellulose chromatography at pH 7.4 and hydroxyapatite column chromatography. Final purification was obtained by using a second DEAE-cellulose column chromatography at pH 6.0. BBP-I activity separated from BBP-II activity during elution from the first DEAE-cellulose column. Purified BBP-II was homogeneous on both polyacrylamide-gel electrophoresis and SDS/polyacrylamide-gel electrophoresis under conditions that would detect a 1% impurity. The subunit Mr determined from SDS/polyacrylamide-gel electrophoresis was 18,200 (72,600 for tetramer), which compares favourably with an Mr value of 17,300 (69,100) calculated from the amino acid analysis. A single precipitin line formed when rabbit antiserum to the protein was directed against a crude chicken egg-yolk sample. BBP-II purified by this procedure lacked carbohydrate and phosphate, was stable indefinitely when frozen, and was quite stable at room temperature. The N-terminal amino acid sequence showed polymorphism at three positions in the first 23 residues and was about 45% identical with the N-terminal 22 residues of avidin. Antiserum to BBP-II cross-reacted with BBP-I and similar proteins in the yolk of eggs from various birds and alligator as judged by immunodiffusion and enzyme-linked immunosorbent assays. No cross-reaction was observed with chicken egg-white by either of these methods.

Circulating levels of biotin in the fowl (Gallus domesticus): modulation by oestrogen

1. Exogenous oestrogen administration to immature male and female chickens significantly increased plasma biotin and significantly reduced liver biotin concentrations. 2. The elevation in plasma biotin concentrations was dose dependent and maximum values were observed 48 hr after a single injection of oestrogen. 3. A second oestrogen injection significantly increased plasma biotin concentrations compared with values obtained after the initial injection given 10 days previously. 4. Plasma biotin concentrations were significantly increased in female, but not male, birds approaching sexual maturity. This increase coincided with the time of the known surge in endogenous oestrogen production by the developing ovary.

Isolation and characterisation of a biotin-binding protein from the pregnant-rat serum and comparison with that from the chicken egg-yolk

A biotin-binding protein exhibiting partial immunological cross-reactivity with the purified chicken egg-yolk biotin-binding protein has been detected, for the first time, in the sera of pregnant/estrogenised female rats but not of the normal males. This protein, purified by affinity chromatography on a biotin-AH-Sepharose was homogeneous by electrophoretic and immunological criteria. It was a glycoprotein of Mr 66,000 without any detectable subunites, had a pI 4.1, and specifically bound [14C]biotin. Several structural and functional features of the biotin-binding protein of rat and chicken were found to be similar. These included immunological cross-reactivity, acidic and glycoprotein nature, ability to tightly bind [14C]biotin, estrogen stimulation for their appearance in circulation, and the pattern of distribution of radioiodinated peptides upon proteolysis with trypsin.

Relationship of biotin deposition in turkey eggs to dietary biotin and biotin-binding proteins

The biotin and biotin-binding protein contents of egg yolk, egg albumen, and hen plasma were determined on eight groups of four turkey hens each that had been fed diets ranging from less than 10 to 3,475 micrograms available biotin per kilogram. Biotin deposition in the yolk was strongly dependent upon available dietary biotin below 100 micrograms/kg. Between 100 and 1,000 micrograms/kg the amount of biotin deposited in the yolk increased slightly and was directly related to and limited by a biotin-binding protein that transferred biotin from the plasma to the yolk. Over the entire dietary range, biotin deposition in yolk was proportional to the total biotin concentration in the plasma. In contrast, biotin deposition in the albumen, which was proportional to dietary biotin, increased several-fold over a very narrow range of plasma biotin concentration (56 to 62 micrograms/L). When dietary available biotin exceeded 160 micrograms/kg, there was more biotin deposited in the albumen than in the yolk. Although the concentration of unbound biotin in plasma is low, it appears to be the component of plasma biotin that is rapidly scavenged by avidin in the oviduct. It seems likely that avidin-bound biotin is available to the turkey embryo.

Role of avidin and other biotin-binding proteins in the deposition and distribution of biotin in chicken eggs. Discovery of a new biotin-binding protein

In addition to the previously characterized egg-yolk biotin-binding protein (BBP-I), we have discovered another BBP (BBP-II) in the plasma and yolk from laying hens. BBP-I is stable to 65 degrees C, whereas BBP-II is stable to 45 degrees C. Both proteins are normally saturated with biotin and together they account for most, if not all, of the biotin in hen plasma and yolk, except in hens fed excessive amounts of biotin (greater than 1 mg of biotin/kg of feed). The maximal production of BBP-I is attained at lower levels of dietary biotin (approximately 50 micrograms/kg) than for BBP-II (approximately 250 micrograms/kg); however, the maximal production of BBP-II is severalfold greater than for BBP-I. Consequently, as dietary biotin increases, the ratio of BBP-II to BBP-I increases and becomes constant at dietary intakes of biotin above 250 micrograms/kg. The observation that the amounts of these proteins are limited by biotin in the normal dietary range (less than 250 micrograms/kg) suggests that biotin is required for the synthesis, secretion or stability of these proteins. Although both plasma vitamin-protein complexes are transported to the oocyte and concentrated in the yolk, BBP-II is transferred more efficiently. Thus biotin deposition in the yolk is a function of the amounts and relative concentrations of the two proteins. Dietary biotin above 250 micrograms/kg exceeds the transport capacity of BBP-I and BBP-II in the plasma; however, unbound biotin does not accumulate. Rather it is efficiently scavenged by avidin in the oviduct and transferred to the egg albumen. Only when avidin becomes saturated at high dietary intake does free or weakly bound biotin accumulate in plasma and yolk. The synthesis of avidin is independent of dietary biotin. Small amounts of BBPs with the heat-stability of avidin or BBP-I respectively are present in the plasma of adult males or immature chickens. BBP-II, the major BBP in the plasma and yolk of laying hens, was not detected in the plasma of non-laying chickens.