Identification of bovine brain Ca2+-binding proteins

The Role of Methionine Oxidation/Reduction in the Regulation of Immune Response

Methionine oxidation by reactive oxygen species and reduction mediated by the methionine sulfoxide reductase (Msr) system may attenuate protein function in signal transduction pathways. This review will focus on two potential protein targets for methionine oxidation involved in signal transduction of the immune response: Ca(2+)/calmodulin-regulated phosphatase calcineurin (Cn) and inhibitor of kappa B-alpha (IkBα). The major known function of Cn is to regulate nuclear localization of the nuclear factor of activated T cells (NFAT), a family of transcription factors during immune stimulus. Like wise, IκBα inhibits the activity of nuclear factor kappa B (NFkB), which is known to regulate the transcription of various genes participating in immunological and oxidative stress response. Modification of Met (45) in IκBα enhances its resistance to protein-degredation; thereby, preventing NFkB from activating transcription in cells of the immune system. Similarly, the human Cn molecule contains several methionine residues that are either located next to a cysteine residue or a methionine residue. Accordingly, it is suggested that oxidation of a specific Cn-methionine may interfere with the proper NFAT nuclear-localization and transcriptional activation in T-cell. Thus, the roles of oxidized-methionine residues and their reduction, by the Msr system, are discussed as potential regulators of cellular immune response.

Chick calretinin: purification, composition, and metal binding activity of native and recombinant forms

Chick calretinin has been previously expressed in Escherichia coli and purified to homogeneity [Cheung, W-T., Richards, D.E., and Rogers, J.H. (1993) Eur. J. Biochem. 215, 401-410]. In the present study we have developed an improved purification procedure, involving a heat precipitation step followed by DEAE-cellulose chromatography with calcium-dependent elution. Native calretinin was purified from chick brainstem using the same method as for the recombinant protein but with an added affinity chromatography step. Typically 30 g of brainstem yielded 350 micrograms of protein. Several differences between the two forms imply that the native protein is acetylated at the N-terminus but otherwise unmodified. The calcium binding activities of both forms of calretinin were measured by equilibrium dialysis with 45Ca in Ca2+/EGTA buffers. The recombinant form bound 4.9 +/- 0.12 calcium ions with Kd = 0.38 +/- 0.02 microM and the native form was not significantly different. Recombinant calretinin was used to study its interaction with other cations present in cells and it was found that calcium binding was affected by Mg2+. Calretinin appears to bind 4.69 +/- 0.13 magnesium ions with Kd = 4.5 mM. Mg2+ increased the apparent dissociation constant for Ca2+. The shift is consistent with competitive binding of Ca2+ and Mg2+ to the same five sites, but Mg2+ binding is too weak to interfere significantly with Ca2+ binding under physiological conditions.

Ca(2+)-binding proteins in rat synaptic fractions surveyed by the 45Ca2+ overlay method

Ca(2+)-binding proteins in the synaptic and subsynaptic fractions (P2, synaptosome, synaptic plasma membrane, and postsynaptic density [PSD]-enriched fractions) and soluble fraction of rat brain were surveyed by a 45Ca2+ overlay method. The PSD-enriched fraction from cerebral cortex contained two major Ca(2+)-binding proteins (55,000 M(r) and 19,000 M(r)) and a distinct group (in 140,000 M(r) region), and two minor ones (66,000 M(r) and 16,000 M(r)); and the fraction from cerebellum contained two (55,000 M(r) and 19,000 M(r)). The proteins with 55,000 M(r) and 19,000 M(r) were identified as tubulin and calmodulin, respectively, and present in all the fractions investigated. The Ca(2+)-binding proteins of 140,000 M(r) region were found only in the PSD-enriched fraction isolated from cerebral cortex: neither the PSD-enriched fraction isolated from cerebellum nor other subcellular fractions prepared from cerebral cortex and cerebellum contained the proteins. The 140,000 M(r) Ca(2+)-binding proteins were the substrates for the Ca2+/calmodulin-dependent protein kinase II associated with PSD, and no change in the Ca(2+)-binding was detected by the 45Ca2+ overlay method after phosphorylation of the proteins by the protein kinase. The 16,000 M(r) Ca(2+)-binding protein might be the beta-subunit of calcineurin. Calretinin and calbindin-D28k were also detected as Ca(2+)-binding proteins in the soluble fractions of both cerebral cortex and cerebellum.

Calcium-binding proteins of boar spermatozoan plasma membranes: identification and partial characterization

Calcium-binding proteins (CBPs) of boar spermatozoa and boar seminal plasma were identified by using a 45Ca overlay technique to detect these proteins on transblots of PAGE-separated proteins. A single CBP (Mr approximately 300 kDa) was detected in seminal plasma. This protein binds specifically to the plasma membrane overlying the principal segment and is removed from sperm during capacitation. The protein was purified for further characterization by anion exchange chromatography and gel filtration. In addition, six major proteins (30, 35, 38, 42, 52, and 66 kDa) which do not originate from accessory gland secretions were found to be strongly associated with the plasma membrane. Most of these proteins are not integral to the membrane and appear to develop an association with the plasma membrane during epididymal maturation. Similarly, calmodulin-binding proteins appear to develop strong associations with the plasma membrane during epididymal transit.

Microtubule-associated protein, MAP2, is a calcium-binding protein

Calcium has been suggested to be an important element in the regulation of microtubule dynamics 'in vivo'. In this report we have analyzed the possibility that microtubule-associated protein 2 (MAP2) binds calcium. MAP2 was blue-stained with the cationic carbocyanine dye 'stains-all' in a similar way to that of calcium-binding proteins and bound 45Ca as estimated from dot-blotting experiments. The calcium-binding characteristics of MAP2, determined by equilibrium dialysis, indicated that MAP2 bound about 3 mol (n = 2.9 +/- 0.4) of calcium per mol of protein (Kd = (0.9 +/- 0.2).10(-5) M). Analysis of the Scatchard plots from equilibrium dialysis and dot-blot assays indicated that MAP2 also presented low-affinity calcium-binding sites (Kd = (0.3 +/- 0.2).10(-4) M). Incubation of nitrocellulose blots of proteolytically digested MAP2 with 45Ca indicated that the calcium-binding sites were located in the region that is not involved in the interaction with tubulin (projection region).

Calretinin: a gene for a novel calcium-binding protein expressed principally in neurons

A novel gene of the calmodulin superfamily, encoding a 29-kD neuronal protein here named "calretinin," has been isolated as a cDNA clone from chick retina. The encoded sequence includes four putative calcium-binding sites and a fusion protein binds calcium. The most similar protein known is the 28-kD intestinal calcium-binding protein, calbindin (58% homology). Both genes date from before the divergence of chicks from mammals. The distribution of calretinin and calbindin mRNAs in chick tissues has been mapped using RNA gel blots and in situ hybridization. RNAs from both genes are abundant in the retina and in many areas of the brain, but calretinin RNA is absent from intestine and other nonneural tissues. Calretinin and calbindin are expressed in different sets of neurons throughout the brain. Calretinin RNA is particularly abundant in auditory neurons with precisely timed discharges.

Identification of a new in vitro substrate of tyrosine protein kinase

Recent studies in our laboratory [Tokuda, M., Khanna, N.C., Aurora, A., & Waisman, D. M. (1986) Biochem. Biophys. Res. Commun. 139, 910-917] have identified in membranes of rat spleen two tyrosine protein kinases named TPK-I and TPK-II. In this paper the identification of the Ca2+ binding protein CAB-48 as a major in vitro substrate of TPK-II is reported. TPK-II catalyzed the incorporation of 0.73 mol of phosphate/mol of CAB-48. Phosphoamino acid analysis revealed that phosphorylation of CAB-48 was specific for tyrosine residues. Phosphorylation of CAB-48 by TPK-I (rat spleen), protein kinase C, casein kinase I, casein kinase II, cAMP-dependent protein kinase, or calcium calmodulin dependent protein kinase was not observed.

Identification of bovine brain calcium binding proteins

Three peaks of calcium binding activity have been identified by the Chelex-100 calcium binding assay of the fractions from DEAE cellulose chromatography of 100,000 X g supernatant of bovine brain. These calcium binding activity peaks have been subjected to extensive purification and three novel calcium binding proteins (Mr 27,000, Mr 48,000 and Mr 63,000) and two previously characterized proteins (calcineurin and calmodulin) have been identified as components of calcium binding activity peaks. Analysis of the calcium binding properties of the novel proteins by equilibrium dialysis suggests these proteins may be intracellular calcium receptors.

Purification and characterization of the 27,000 Da calcium-binding protein of bovine brain

A Ca2+-binding protein named CAB-27 was purified from bovine brain 100,000 g supernatant. The protein has a molecular mass of 27,000 Da as determined by SDS/polyacrylamide-gel electrophoresis and 35,500 Da by sedimentation-coefficient and Stokes-radius analysis. The protein contains about 26% Glx and Asx and 13% basic residues. The acidic nature of the molecule is confirmed by its pI of 4.80. In the presence of 3 mM-MgCl2 and 150 mM-KCl, CAB-27 binds 2.0 mol of Ca2+/mol of protein, with an apparent Kd of 0.2 microM. Ca2+-binding is unaffected by prior incubation of the protein at 80 degrees C for 2 min. Brain contains about 130 mg of CAB-27/kg. Immunoblotting identified CAB-27 in several bovine tissues; it appears to be particularly rich in brain and kidney. In addition, CAB-27 is identified as an inhibitor of bovine pancreas phospholipase A2 in vitro. The inhibitory activity of CAB-27 was 20-fold less potent than lipocortin. On the basis of the Ca2+-binding properties, intracellular concentration and tissue distribution of this protein, we suggest that CAB-27 may be an important intracellular Ca2+ receptor.

Purification of three forms of lipocortin from bovine lung

Experimental conditions are described for simultaneous purification of three forms of lipocortin (lipocortin I, lipocortin II and lipocortin-85) from bovine lung. The procedure yields milligram quantities of all three lipocortins. Using antisera against lipocortin I and lipocortin II, purified proteins show no cross contaminations. All forms of lipocortin exhibit equal potency as in vitro bovine pancreatic phospholipase A2 inhibitors. Protein kinase C catalyzes the in vivo incorporation of about 1.0, 0.7 and 0.4 mole of phosphate per mole of lipocortin I (p35), lipocortin II (p36) and lipocortin-85 (p36 oligomer) respectively. The phosphorylation is specific for protein kinase C and is dependent on the presence of both calcium and phospholipids. While lipocortin I is phosphorylated on threonine residues, lipocortin II and lipocortin-85 are phosphorylated on serine residues.

Identification of a major bovine heart Ca2+ binding protein

The 100,000 x g supernatant of bovine heart has been chromatographed on DEAE-cellulose and the resultant fractions have been analyzed for both calcium binding activity and calmodulin activity. Of the four peaks of calcium binding activity detected by this procedure only a single peak (peak IV) was identified as calmodulin. The calcium binding activity of the largest peak (peak III) has been subjected to further purification and a single calcium binding protein of Mr 63,000 isolated. Biochemical and immunological results documented that the 63 kDa protein is identical to calregulin. The results of this study identify calregulin as a major bovine heart calcium binding protein.

Inhibition of phospholipase A2 by protein I

The 36 kDa substrate of several tyrosine protein kinases has been shown to exist in monomeric and oligomeric (362102) forms. Partial sequence data has suggested that the oligomer, referred to as protein I, is homologous to a group of phospholipase A2 inhibitory proteins, collectively called lipocortins. In the present communication we demonstrate that protein I inhibits bovine pancreas phospholipase A2 with similar potency to that of lipocortin. Approximately 44 pmol protein I was required to produce 50% inhibition of 7.2 pmol of phospholipase A2. Inhibition of phospholipase A2 activity by calmodulin, S-100, calregulin, parvalbumin, troponin-C, or CAB-48 was not observed. These results indicate that protein I is a potent and specific inhibitor of phospholipase A2 activity, and thus shares functional homology with the lipocortin proteins. We therefore propose that this protein be named lipocortin-85.

A calcium binding protein from Drosophila melanogaster which activates cAMP phosphodiesterase: comparison of this protein with porcine brain calmodulin

A calcium binding protein from Drosophila melanogaster has been isolated and characterized. This protein shows several analogies with pig brain calmodulin in its molecular weight, isoelectric point, peptide maps, calcium binding properties, and ability to activate cyclic AMP phosphodiesterase. However, some differences were observed; the most remarkable one is the presence of tryptophan, an amino acid which is absent from all the calmodulins analyzed previously.