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Influence of monovalent cations on rat alpha- and beta-parvalbumin stabilities.

The mammalian genome encodes both alpha- and beta-parvalbumin isoforms. The rat beta-parvalbumin (aka "oncomodulin") is more stable than the alpha isoform at physiological pH and ionic strength, despite its substantially higher charge density and truncated C-terminal helix [Henzl, M. T., and Graham, J. S. (1999) FEBS Lett. 442, 241-245]. Reasoning that solvent interactions could contribute to this unexpected finding, we have examined the stabilities of the Ca(2+)-free alpha- and beta-parvalbumins as a function of Na(+) and K(+) concentration. Differential scanning calorimetry data suggest that, at physiological pH and ionic strength, the beta isoform binds roughly 2 equiv of Na(+) or a single equivalent of K(+) with moderate affinity. Under comparable conditions, the alpha isoform apparently binds just 1 equiv of Na(+) and essentially no K(+). Isothermal titration calorimetry experiments suggest that the bound monovalent ions occupy the EF-hand motifs. In 0.15 M K(+), at pH 7.4, the stability of the apo-beta-parvalbumin exceeds that of the alpha isoform by approximately 2.6 kcal/mol at 37 degrees C and by approximately 3.0 kcal/mol at 25 degrees C. The latter value represents a substantial fraction of the difference in Ca(2+)-binding free energies measured in vitro for the two proteins. Significantly, however, these results do not completely explain the paradoxical stability of the beta isoform, which maintains its higher melting temperature under all conditions examined.

Amino Acid Sequence↗

Detection of a beta-parvalbumin isoform in the mammalian inner ear.

A small, acidic calcium-binding protein (CBP-15) has been detected in the guinea pig organ of Corti, the auditory receptor organ. The apparent molecular weight (15,000) and very low isoelectric point (pI approximately 3.1) suggest that CBP-15 is a beta-parvalbumin isoform. Consistent with this hypothesis, CBP-15 exhibits extreme homology to the mammalian oncofetal parvalbumin called oncomodulin. Sequence data have now been obtained for 30 residues in the N-terminal third of CBP-15. Identity with oncomodulin is observed at all 30 positions. This finding could necessitate revision of the assumption that postnatal mammals utilize a single alpha-parvalbumin isoform in muscle and nonmuscle settings alike.

Amino Acid Sequence↗

Conformational stabilities of the rat alpha- and beta-parvalbumins.

It is widely believed that beta-parvalbumin (PV) isoforms are intrinsically less stable than alpha-parvalbumins, due to greater electrostatic repulsion and an abbreviated C-terminal helix. However, when examined by differential scanning calorimetry, the apo-form of the rat beta-PV (i.e. oncomodulin) actually displays greater thermal stability than the alpha-PV. Whereas the melting temperature of the a isoform is 45.8 degrees C at physiological pH and ionic strength, the Tm for the beta isoform is more than 7 degrees higher (53.6 degrees C). This result suggests that factors besides net charge and C-terminal helix length strongly influence parvalbumin conformational stability. Extension of the F helix in the beta-PV, by insertion of Ser-109, has a modest stabilizing effect, raising the Tm, by 1.1 degrees. Truncation of the alpha-PV F helix, by removal of Glu-108, has a more profound impact, lowering the Tm by 4.0 degrees.

Animals↗

15N nuclear magnetic resonance relaxation studies on rat beta-parvalbumin and the pentacarboxylate variants, S55D and G98D.

15N relaxation data for Ca(2+)-bound rat beta-parvalbumin (a.k.a. oncomodulin) were analyzed using the Lipari-Szabo formalism and compared with existing data for rat alpha-parvalbumin. Although the average S(2) values for the two proteins are very similar (0.85 for alpha, 0.84 for beta), residue-by-residue inspection reveals systematic differences. alpha tends to have the lower S(2) value in helical regions; beta tends to have the lower value in the loop regions. Rat beta was also examined in the Ca(2+)-free state. The 59 assigned residues displayed an average order parameter (0.90) significantly greater than the corresponding residues in the Ca(2+)-loaded form. The pentacarboxylate variants of rat beta-S55D and G98D-also were examined in the Ca(2+)-bound state. Although both mutations significantly heighten Ca(2+) affinity, they utilize distinct energetic strategies. S55D improves the Ca(2+)-binding enthalpy; G98D improves the binding entropy. They also show disparate peptide backbone dynamics. Whereas beta G98D displays an average order parameter (0.87) slightly greater than that of the wild-type protein, beta S55D displays an average order parameter (0.82) slightly lower than wild-type beta. Furthermore, whereas just two backbone N-H bonds in beta G98D show internal motion on the 20-200-psec timescale, fully 52 of the 93 residues analyzed in beta S55D show this behavior. These findings suggest that the increased electrostatic repulsion attendant to introduction of an additional carboxylate into the CD site ligand array impedes backbone vibrational motion throughout the molecule.

Amino Acid Sequence↗

1H NMR spectroscopic studies of calcium-binding proteins. 2. Histidine microenvironments in alpha- and beta-parvalbumins as determined by protonation and laser photochemically induced dynamic nuclear polarization effects.

The microenvironments of the histidines in three isoforms of Ca(II)-bound parvalbumin (carp, pI = 4.25; pike, pI = 5.00; rat, pI = 5.50) have been examined with 1H NMR techniques to probe their protonation characteristics and photochemically induced dynamic nuclear polarizability (photo-CIDNP). The histidine at position 26 (or 25), present in all three of these proteins, shows absolutely no photo-CIDNP enhancement of its C2H or C5H resonances. Nor does this nonpolarizable histidine possess a normal pKa: values range only from 4.20 for carp to 4.32 for pike to 4.44 for rat. The C2H and C5H resonances of the histidine in this carp isoform split into doublets as the pH is lowered. The magnitude of this splitting depends on the magnetic field strength, temperature, and pH; however, the line intensities within each doublet are temperature-independent. Although the crystal structure of carp parvalbumin indicates that His-26 is exposed to solvent [Kretsinger, R. H., & Nockolds, C. E. (1973) J. Biol. Chem. 248, 3313-3326], we conclude that in solution this residue, in its unprotonated state, is part of the hydrophobic core of the protein. In contrast, His-48 in rat parvalbumin and His-106 in pike III parvalbumin show dramatic photo-CIDNP enhancements of their C2H, C5H, and beta-CH2 1H NMR resonances. Combined with its nearly normal pKa, 6.14, and exchange-broadened C2H resonance, the photo-CIDNP enhancement results for His-48 indicate that its microenvironment differs little from random-coil exposure, consistent with its presumed position on the solvent surface of helix C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Crystal structure of the unique parvalbumin component from muscle of the leopard shark (Triakis semifasciata). The first X-ray study of an alpha-parvalbumin.

The three-dimensional structure of parvalbumin from leopard shark (Triakis semifasciata) with 109 amino acid residues (alpha-series) is described at 1.54 A resolution. Crystals were grown at 20 degrees C from 2.9 M-potassium/sodium phosphate solutions at pH 5.6. The space group is P3(1)21 and unit cell dimensions are a = b = 32.12 A and c = 149.0 A. The structure has been solved by the molecular replacement method using pike 4.10 parvalbumin as a model. The final structure refinement resulted in an R-factor of 17.3% for 11,363 independent reflections at 1.54 A resolution. The shark parvalbumin shows the main features of all parvalbumins: the folding of the chain including six alpha-helices, the salt bridge between Arg75 and Glu81, and the hydrophobic core. Compared to the structure of beta-parvalbumins from pike and carp, one main difference is observed: the chain is one residue longer and this additional residue, which extends the F helix, is involved through its C-terminal carboxylate group in a network of electrostatic contacts with two basic residues, His31 in the B helix and Lys36 in the BC segment. Furthermore, hydrogen bonds exist between the side-chains of Gln108 (F helix) and Tyr26 (B helix). There is therefore a "locking" of the tertiary structure through contacts between two sequentially distant regions in the protein and this is likely to contribute to making the stability of an alpha-parvalbumin higher in comparison to that of a beta-parvalbumin. The lengthening of the C-terminal F helix by one residue appears to be a major feature of alpha-parvalbumins in general, owing to the homologies of the amino acid sequences. Besides the lengthening of the C-terminal helix, the classification of the leopard shark parvalbumin in the alpha-series rests upon the observation of Lys13, Leu32, Glu61 and Val66. As this is the first crystal structure description of a parvalbumin from the alpha-phylogenetic lineage, it was hoped that it would clearly determine the presence or absence of a third cation binding site in parvalbumins belonging to the alpha-lineage. In beta-pike pI 4.10 parvalbumin, Asp61 participates as a direct ligand of a third site, the satellite of the CD site. In shark parvalbumin, as in nearly all alpha-parvalbumins, one finds Glu at position 61. Unfortunately, the conformation of the polar head of Glu61 cannot be inferred from the X-ray data.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

Severe IgE-mediated anaphylaxis following consumption of fried frog legs: definition of alpha-parvalbumin as the allergen in cause.

BACKGROUND: IgE-mediated allergic reactions to bullfrog and edible frog have been reported. The implicated allergens have not been defined so far. The frog material and the patient's serum from a case of severe food-induced anaphylaxis were used to define the implicated allergen at the protein and DNA level. METHODS: Immunoblotting techniques and N-terminal protein microsequencing were used to define the allergen recognized by the patient's serum. Back translation from the identified protein sequence was used to design degenerated primers to amplify the allergen's cDNA by polymerase chain reaction (PCR). We defined the nucleotide sequence of the allergen from the frog of Indonesian origin that was consumed by the patient, and the homologous cDNA from Rana esculenta. RESULTS: Protein microsequencing revealed that the implicated frog allergen belonged to the parvalbumin family. cDNAs coding for alpha- and beta-parvalbumin of R. esculenta and Rana species were cloned. Recombinant proteins were expressed in Escherichia coli. The patient's serum IgE antibodies recognized parvalbumin prepared from frog muscle and recombinant alpha-parvalbumin from R. species but not from R. esculenta. Recombinant beta-parvalbumin was not recognized by the IgE antibodies. CONCLUSION: This work defines at the protein and DNA levels alpha-parvalbumin as the allergen implicated in a case of IgE-mediated anaphylaxis to frog muscle. It also shows that a protein belonging to the parvalbumin family is implicated in type I allergies outside the fish species.

Allergens↗

A metagenomic analysis of the gut microbiota in a mouse model of fish allergy.

BACKGROUND: Fish are among the most frequent causes of immunoglobulin E (IgE)-mediated food allergies (Type I). Currently, there is no known cure for fish allergy and individuals who are sensitized have to practice strict, lifelong avoidance of fish products in their diets. The relationship between gut microbiome and food allergies is currently a major topic of discussion; these pathologies involve the development of dysbiosis, which is a microbial imbalance resulting from immune-related mechanisms. Recent studies have provided evidence that individuals suffering from food allergies, display an intestinal microbiota with a different microbial composition compared to healthy subjects. OBJECTIVES AND METHODS: In this work, we have described for the first time the differences in microbiome composition in a mouse model of fish allergy with previous sensitization to the main allergen, beta-Parvalbumin (β-PRVB), compared to mouse individuals without allergic response. RESULTS: The metagenomic analysis has shown differences in taxonomic composition between the treatments. Regarding phyla, an increase in the relative abundance of Patescibacteria, specifically Saccharimonas genus and Candidatus_Saccharimonas group, were observed in the allergic animals (Prvb_Alum group) when compared to the other groups. In contrast, the relative abundance of the RF39 group (Bacilli), Atopobiaceae family, Erysipelotrichaceae, and the Coriobacteriaceae_UCG-002 group, was higher in the animals that did not develop an allergic response, despite being exposed to the allergen (Prvb group). Furthermore, an increase in the relative abundance of Lachnospiraceae ASF356 group was observed in the control group compared to the other treatments. This family, has been reported to be inversely associated with the progression of intestinal inflammation and anaphylactic diseases. For the first time, the gut microbiota composition of individual mice with and without fish allergies is described in detail in this work. This study may shed light on the potential contribution of gut microbiota to the onset and avoidance of food allergies.

beta-parvalbumin↗

Calbindin-d(28k): a marker of recurrence for medulloblastomas.

BACKGROUND: The expression of the Ca(2+)-binding protein calbindin-D(28k) was analyzed in medulloblastomas in relation to clinical features and other biologic markers related to cell proliferation, differentiation, p53, and cerebellar developmental regulated gene expression. METHODS: Immunohistochemistry was carried out on histologic slides from a first retrospective series of 29 nonmetastatic and 10 metastatic medulloblastoma formalin-fixed, paraffin-embedded tissues, using specific antibodies against calbindin-D(28k), calretinin, alpha-parvalbumin and beta-parvalbumin, and S100 proteins. Informed consent was obtained from the subjects and/or guardians. Other biologic markers for differentiation, cell proliferation, the expression of the p53 tumor suppressor gene protein, and cerebellar developmental regulated genes were similarly investigated. A second series of 16 medulloblastomas from young patients (younger than 15 years) was added in order to validate the results obtained in the first series. RESULTS: Of all the markers investigated, only calbindin-D(28k) was significantly associated with prognosis. Survival and remission (i.e. recurrence free) time analysis performed on all the cases (n = 55) confirmed a high risk of death (P = 0.004) and recurrence (P = 0.003) associated with calbindin-positivity. As calbindin-positivity was predominantly observed in tumors from young patients, the authors confirmed its prognostic value in the subgroup of patients younger than 15 years (n = 37). Cox regression analysis showed a significant and independent prognostic value for calbindin expression and, to a lesser extent, the type of surgery (total or subtotal). Three risk groups were thus identified, distinguishing among the cases characterized by a total resection and calbindin-negativity (good prognosis), by a subtotal resection and calbindin-negativity (intermediary), and by calbindin-positivity (bad prognosis). CONCLUSIONS: The current study suggests that calbindin-positive medulloblastomas represent a subclass of aggressive tumors more frequently seen in younger patients.

Adolescent↗

A new member of the troponin C superfamily: comparison of the primary structures of rat oncomodulin and rat parvalbumin.

When the amino-acid sequence of the 108-residue, rat tumour calcium-binding protein, oncomodulin, was aligned with that of rat muscle parvalbumin, 55 homologous positions were found, with an additional 33 single base-pair substitutions. This extensive homology, with virtual identity of the calcium-binding domains, signalled oncomodulin to be a member of the troponin C superfamily. The presence of Cys-18 and Phe-66 in oncomodulin, plus its isoelectric point of 3.9, suggest that this tumour protein is a beta-parvalbumin, rather than a muscle alpha-parvalbumin.

Amino Acid Sequence↗

Parvalbumins from coelacanth muscle. III. Amino acid sequence of the major component.

The primary structure of the major parvalbumin (pI = 4.52) from coelacanth muscle (Latimeria chalumnae) has been determined. Sequence analysis of the tryptic peptides, in some cases obtained with beta-trypsin, accounts for the total amino acid content of the protein. Chymotryptic peptides provide appropriate sequence overlaps, to complete the localization of the tryptic peptides. Examination of the amino acid sequence of this protein shows the typical structure of a beta-parvalbumin. Its position in the dendrogram of related calcium-binding proteins corresponds to that usually accepted for crossopterygians.

Amino Acid Sequence↗

Oncomodulin is abundant in the organ of Corti.

A small, acidic Ca(2+)-binding protein (CBP-15) was recently detected in extracts of the mammalian auditory receptor organ, the organ of Corti [Senarita et al. (1995) Hear. Res. 90, 169-175]. N-terminal sequence data for CBP-15 [Thalmann et al. (1995) Biochem. Biophys. Res. Commun. 215, 142-147] implied membership in the parvalbumin family and possible identity with the mammalian beta-parvalbumin oncomodulin. As shown herein, the latter conclusion is supported by strong cross-reactivity between CBP-15 and isoform-specific antibodies to oncomodulin. Moreover, we have succeeded in amplifying the guinea pig CBP-15 coding sequence from organ of Corti cDNA using degenerate oligonucleotide primers based on the rat oncomodulin sequence. The deduced amino acid sequence of guinea pig CBP-15 displays 90%, 92%, and 98% identity with mouse, rat, and human oncomodulin isoforms. Demonstration of the presence of oncomodulin in the organ of Corti is the first documentation of this substance in a postnatal mammalian tissue.

Amino Acid Sequence↗

Interconversion of the ligand arrays in the CD and EF sites of oncomodulin. Influence on Ca2+-binding affinity.

The parvalbumin metal ion-binding sites differ at the +z and -x residues: Whereas the CD site employs serine and glutamate (or aspartate), respectively, the EF site employs aspartate and glycine. Although frequently indistinguishable in Ca2+- and Mg2+-binding assays, the CD and EF sites nonetheless exhibit markedly different preferences for members of the lanthanide series [Williams et al. (1984) J. Am. Chem. Soc. 106, 5698-5702], underscoring an intrinsic nonequivalence. This nonequivalence reaches its pinnacle in the mammalian beta-parvalbumin (oncomodulin). Whereas the oncomodulin EF site exhibits the expected Ca2+/Mg2+ signature, the Ca2+ affinity of the CD site is severely attenuated. To obtain insight into the structural factors responsible for this reduction in binding affinity, oncomodulin variants were examined in which the CD and EF site ligand arrays had been exchanged. Our data suggest that binding affinity may be dictated either by ligand identity or by the binding site environment. For example, the Ca2+ affinity of the quasi-EF site resulting from the combined S55D and D59G mutations is substantially lower than that of the authentic EF site. This finding implies that other local environmental variables (e.g., binding loop flexibility, electrostatic potentials) within the CD binding site supersede the influence of ligand identity. However, the CD site ligand array does not acquire a high-affinity signature when imported into the EF site, as in the D94S/G98D variant. Instead, it retains its Ca2+-specific signature, implying that this constellation of ligands is less sensitive to placement within the protein molecule. The D59G and D94S single mutations substantially lower binding affinity, consistent with removal of a liganding carboxylate. By contrast, the S55D and G98D mutations substantially increase binding affinity, a finding at odds with corresponding data collected on model peptide systems. Significantly, the Ca2+ affinity of the oncomodulin CD site is increased by mutations that weaken binding at the EF site, indicating a negatively cooperative interaction between the two sites.

Amino Acid Substitution↗

A new oligomeric parvalbumin allergen of Atlantic cod (Gad mI) encoded by a gene distinct from that of Gad cI.

BACKGROUND: The major allergen of Baltic cod (Gadus callarias) is a 12.3-kDa parvalbumin with two calcium-binding sites corresponding to EF-hand motifs. Our group found a 24-kDa IgE-reactive band that was also recognized by a monoclonal antiparvalbumin antibody in Atlantic cod (Gadus morhua). Our purpose was to purify and to determine the cDNA deduced sequence of this new cod allergen. METHODS: Proteins from pre rigor mortis Atlantic cod were separated by gel filtration and the eluted peaks were analysed by SDS-PAGE and Western blotting with sera of sensitized patients and with antiparvalbumin. Protein bands were microsequenced, RNA transcripts were amplified by reverse transcription and polymerase chain reaction (RT-PCR) using primer combinations overlapping the open reading frame. RESULTS: Four IgE and antiparvalbumin reactive proteins(12.5, 24, 38 and 51 kDa) were detected in gel filtration eluate. The cDNA deduced sequence of the 24 kDa protein had 109 amino acid residues with a molecular weight of 11.5 kDa and a theoretical pI of 4.34. The 24 kDa band corresponded therefore to a dimer of a beta-parvalbumin. Its homology was higher with Sal sI than with Gad cI. This new allergen was named Gad mI. CONCLUSION: We have characterized a new parvalbumin allergen in Gadus morhua. This protein formed oligomers in native and in reducing conditions. Gad mI and Gad cI may correspond to two distinct genes of Gadus species.

Allergens↗

Expression of the Ca2+-binding protein, parvalbumin, during embryonic development of the frog, Xenopus laevis.

A cDNA segment encoding the Ca2+-binding protein, parvalbumin, was isolated with the use of antibodies, from a lambda gtll expression library of Xenopus laevis tadpole poly(A)+ RNAs. The bacterially expressed beta-galactosidase-parvalbumin fusion protein of one lambda recombinant shows high affinity 45Ca2+ binding. The sequence of the tadpole parvalbumin is highly similar to previously characterized beta-parvalbumins of other organisms. Data from protein and RNA blotting experiments demonstrate that parvalbumin is absent in oocytes, eggs, and early staged embryos, and only becomes expressed during embryogenesis at the time of myogenesis. The protein can be detected in individual developing muscle cells and in muscle fibers of tadpole tail muscles. A simple method is also described for the isolation of neural tube-notochord-somite complexes from Xenopus embryos.

Amino Acid Sequence↗

Preparation and characterization of two major isotypes of parvalbumins from skeletal muscle of bullfrog (Rana catesbeiana).

Two major isotypes of parvalbumins (PA1 and PA2) have been isolated from the skeletal muscle of bullfrog, Rana catesbeiana. The Mr values were estimated to be 10,100 (PA1) and 11,800 (PA2) by SDS/polyacrylamide gel electrophoresis, and the isoelectric points were determined to be 4.78 (PA1) and 4.97 (PA2) by polyacrylamide gel isoelectric focusing. The amino acid compositions and isoelectric points indicate that PA1 corresponds to Rana esculenta pI 4.50 and Rana temporaria pI 4.75 parvalbumins and PA2 to Rana esculenta pI 4.88 and Rana temporaria pI 4.97 parvalbumins, showing that PA1 is genetically a beta-parvalbumin and PA2 an alpha-parvalbumin. However, in terms of the amino acid compositions, PA1 and PA2 are distinctly different from the corresponding parvalbumins of Rana esculenta or Rana temporaria. The ultraviolet spectra of PA1 and PA2 are consistent with their amino acid compositions. An ultraviolet difference spectrum of the Ca2+-loaded form vs. metal-free form indicates that a Tyr and some Phe residues in PA1 are affected by a conformational change associated with the binding of Ca2+. On electrophoresis in polyacrylamide gel in 14 mM Tris and 90 mM glycine, the Ca2+-loaded form of PA1 migrated twice as fast as the Mg2+-loaded form. Both PA1 and PA2 show increased mobility in the Ca2+-loaded forms, like troponin C but different from calmodulin.

Amino Acids↗

Amino-acid sequence of an alpha-parvalbumin, pI = 4.88, from frog skeletal muscle.

The primary structure of the most basic (pI = 4.88) of the two major parvalbumins from frog skeletal muscle (Rana esculenta) has been determined by partial automatic sequencing of the protein which exhibits a free N terminus, and a study of overlapping peptides obtained by cyanogen bromide cleavage and digestion with trypsin, thermolysin and Armillaria mellea protease. This protein shows the typical structure of an alpha-parvalbumin. Comparison of the primary structure of ion-binding loops of alpha and beta-parvalbumins does not provide a clear-cut explanation of their differences in ion-binding properties.

Agaricales↗

Specific proteins of the organ of Corti.

The mammalian organ of Corti has achieved a degree of perfection unequaled in other hair cell systems. Although cellular metabolism requires the coordinated action of thousands of proteins, the physical processes underlying auditory transduction in the OC are undoubtedly mediated by a much smaller subset of these. OCP1, OCP2, and CBP-15-identified by 2D-PAGE-are apparently members of this elite class. OCP1 and OCP2 are restricted to the supporting cells of the organ of Corti and adjacent epithelia. Their distribution closely parallels the boundaries of the epithelial gap junction system, implying a role in cochlear potassium and pH homeostasis. CBP-15 was recently shown to be identical to oncomodulin, the mammalian beta-parvalbumin, heretofore documented only in the placenta and neoplasms. Expression of this small calcium-binding protein in the OC is restricted to the outer hair cells, where it may function as a calcium-dependent regulatory protein.

Animals↗