Calmodulin-binding proteins: visualization by 125I-calmodulin overlay on blots quenched with Tween 20 or bovine serum albumin and poly(ethylene oxide)

Identification of Ca2+-dependent calmodulin-binding proteins in rat spermatogenic cells as complexes of the heat-shock proteins

Ca2+-calmodulin (CaM)-binding proteins in rat testes were characterized by assays for CaM-binding activity using the CaM-overlay method on transblots of electrophoresed gels and purification by gel-filtration, ion exchange, and adsorption chromatographies. A major CaM-binding protein complex (CaMBP) was identified and found to be comprised of three proteins with molecular masses 110, 100, and 70 kDa. Amino acid sequence analyses of lysylendopeptidase digests from these proteins indicated that all of the constituents of CaMBP are very similar to the members of the heat-shock protein family, i.e., the 110-kDa protein is similar to the APG-2/94 kDa rat ischemia-responsive protein, the 100-kDa protein is similar to the rat counterpart of the mouse APG-1/94 kDa osmotic stress protein, and the 70-kDa protein is similar to the rat testis-specific major heat-shock protein (HSP70). Immunohistochemistry using anti-CaMBP and anti-CaM antibodies demonstrated that CaMBP was co-localized with CaM in the cytoplasm of pachytene spermatocytes and nuclei of round spermatids. In addition, CaMBP, but not CaM, was localized at a high level in the residual bodies of elongated spermatids. The possible relevance of CaMBP to regulation of cell cycle progression and spermatogenesis is discussed in this paper.

Distribution and localization of calmodulin-binding proteins in bull spermatozoa

Previous studies from our laboratory have shown that a decrease in the calmodulin binding properties of a few sperm proteins occurs during the capacitation process, an effect associated with a decrease in intracellular calmodulin concentrations. Using biotinylated-calmodulin nitrocellulose overlay assay on protein extracts of subcellular fractions of bull spermatozoa, one of these proteins (p32) is detected in the flagellar-enriched fractions, whereas p30 is found in the fraction enriched with sperm heads. This latter calmodulin binding protein, p30, appears to be associated with the perinuclear theca. None of these binding proteins was solubilized by nonionic detergents. Sodium dodecyl sulfate was effective solubilizing p32, whereas p30 was extracted only in conditions reported to isolate the perinuclear theca. Cellular localization of calmodulin binding proteins was also achieved by incubating spermatozoa fixed on slides with biotinylated calmodulin and revealed in a further step by fluorescein-conjugated streptavidin. Using this procedure, it was found that calmodulin binds to the sub- and postacrosomal areas of the sperm head along with the midpiece in the presence of Ca(2+). Only a sharp band of fluorescence at the subacrosomal area was observed when this procedure was performed in the absence of Ca(2+) in the presence of EGTA. The pattern of cellular calmodulin binding was highly decreased when spermatozoa were incubated under capacitating conditions, in the presence of heparin, in agreement with the published effect of capacitation on calmodulin binding proteins.

A myosin III from Limulus eyes is a clock-regulated phosphoprotein

The lateral eyes of the horseshoe crab Limulus polyphemus undergo dramatic daily changes in structure and function that lead to enhanced retinal sensitivity and responsiveness to light at night. These changes are controlled by a circadian neural input that alters photoreceptor and pigment cell shape, pigment migration, and phototransduction. Clock input to the eyes also regulates photomechanical movements within photoreceptors, including membrane shedding. The biochemical mechanisms underlying these diverse effects of the clock on the retina are unknown, but a major biochemical consequence of activating clock input to the eyes is a rise in the concentration of cAMP in photoreceptors and the phosphorylation of a 122 kDa visual system-specific protein. We have cloned and sequenced cDNA encoding the clock-regulated 122 kDa phosphoprotein and show here that it is a new member of the myosin III family. We report that Limulus myosin III is similar to other unconventional myosins in that it binds to calmodulin in the absence of Ca2+; it is novel in that it is phosphorylated within its myosin globular head, probably by cAMP-dependent protein kinase. The protein is present throughout the photoreceptor, including the region occupied by the photosensitive rhabdom. We propose that the phosphorylation of Limulus myosin III is involved in one or more of the structural and functional changes that occur in Limulus eyes in response to clock input.

Two major autoantigen-antibody systems of the mitotic spindle apparatus

OBJECTIVE

To characterize human autoantigen-antibody systems related to the mitotic poles and spindles.

METHODS

Thirty-seven human sera with autoantibodies staining mitotic poles and spindles in indirect immunofluorescence (IIF) studies were further characterized by immunofluorescence on mitotic cells and by immunoblotting and immunoprecipitation. Clinical diagnoses meeting the American College of Rheumatology criteria were based on chart review and interview with the corresponding physicians.

RESULTS

Two autoantibody systems reactive with mitotic poles and spindles were defined. Type 1 nuclear mitotic apparatus (NuMA-1) antibodies were identified in the serum of 30 patients. Interphase cells showed a fine, speckled, nuclear staining, while mitotic cells had bright staining of the rim of the centrosomes and light staining of the spindles proximal to the centrosomes. In telophase, the staining shifted from the centrosomes to the reforming nuclei. On immunoblotting, anti-NuMA-1 sera reacted with a 210-kd protein. The reactivity of these sera was identified (with the aid of reference antibodies) as the previously described NuMA antigen-antibody system. Clinical information was available for only 17 of the 30 patients with anti-NuMA-1; of these, 17 (53%) had clinical and lip biopsy findings that met the criteria for Sjögren's syndrome. NuMA-2 antibodies were found in the sera of 7 patients. Interphase cells showed no nuclear or cytoplasmic staining, but mitotic cells had brightly stained poles and spindles. At anaphase/telophase, staining shifted to the midbody and the intercellular bridge. Anti-NuMA-2 sera immunoprecipitated a protein of 116 kd. This group of patients was more heterogeneous and had both systemic and organ-specific autoimmune diseases.

CONCLUSIONS

NuMA protein (here called NuMA-1) and a 116-kd protein (here called NuMA-2) are the major targets of the autoimmune response in the mitotic apparatus, since most of the selected sera (based on IIF staining of the mitotic spindles and poles) recognized 1 of these 2 antigens.

Characterization of the actin cross-linking properties of the scruin-calmodulin complex from the acrosomal process of Limulus sperm

During activation of the Limulus sperm acrosomal process, actin filaments undergo a change in twist that is linked with the conversion from a coiled to a straight scruin-actin bundle. Since scruin had not been purified, its identity as an actin-binding protein has not been demonstrated. Using HECAMEG (methyl-6-O-(N-heptyl-carbamoyl)-alpha-D-glucopyranoside) detergent extraction in concert with high calcium, we purified native scruin and identified it as an equimolar complex with calmodulin. 125I-Calmodulin overlays and calmodulin-Sepharose indicate that scruin binds calmodulin in calcium but not in EGTA. Overlay experiments also map the calmodulin binding site between the putative N- and C-terminal beta-propeller domains within residues 425-446. Immunofluorescence microscopy reveals that calmodulin colocalizes with scruin and actin in the coiled bundle. Although scruin binds calmodulin, pelleting assays and electron microscopy show that the scruin cross-links F-actin into bundles independently of calcium. Based on our biochemical and structural studies, we suggest a model to explain how scruin controls a change in twist of actin filaments during the acrosome reaction. We predict that calcium subtly alters scruin conformation through its calmodulin subunit and the conformation change in scruin causes a shift in the relative positions of the scruin-bound actin subunits.

Studying the interaction of polyoma virus middle T antigen with cellular proteins

The oncogenic mouse polyoma virus encodes six proteins, two of which (the large and middle T antigens), when expressed together in primary rodent cells, generate an alteration of growth patterns commonly known as cellular transformation. The transformed cells grow with an unlimited life span and when introduced into immunocompromised mice rapidly form tumours. The large T gene product confers an indefinite growth potential on primary cells; however, the middle T gene product has been identified as bringing about the changes which ultimately allow the cell to form tumours. The 55 kDa middle T antigen has been shown to associate with a number of cellular enzymes involved in regulation of growth factor signalling pathways, all of which were identified as being components of the immunocomplexes that can be isolated from transformed cells using middle T antigen specific antibodies. Two-dimensional gels have assisted the search for less prominent species present in these complexes. These methods represents one approach to investigating associating proteins, and as such, select for those interactions that are stable under the conditions used. In order to explore the possibility that middle T antigen could form complexes with other cellular proteins given different conditions, recombinant middle T antigen was used in a series of "filter overlay" experiments.

A role for the dystrophin-glycoprotein complex as a transmembrane linker between laminin and actin

The dystrophin-glycoprotein complex was tested for interaction with several components of the extracellular matrix as well as actin. The 156-kD dystrophin-associated glycoprotein (156-kD dystroglycan) specifically bound laminin in a calcium-dependent manner and was inhibited by NaCl (IC50 = 250 mM) but was not affected by 1,000-fold (wt/wt) excesses of lactose, IKVAV, or YIGSR peptides. Laminin binding was inhibited by heparin (IC50 = 100 micrograms/ml), suggesting that one of the heparin-binding domains of laminin is involved in binding dystroglycan while negatively charged oligosaccharide moieties on dystroglycan were found to be necessary for its laminin-binding activity. No interaction between any component of the dystrophin-glycoprotein complex and fibronectin, collagen I, collagen IV, entactin, or heparan sulfate proteoglycan was detected by 125I-protein overlay and/or extracellular matrix protein-Sepharose precipitation. In addition, laminin-Sepharose quantitatively precipitated purified dystrophin-glycoprotein complex, demonstrating that the laminin-binding site is accessible when dystroglycan is associated with the complex. Dystroglycan of nonmuscle tissues also bound laminin. However, the other proteins of the striated muscle dystrophin-glycoprotein complex appear to be absent, antigenically dissimilar or less tightly associated with dystroglycan in nonmuscle tissues. Finally, we show that the dystrophin-glycoprotein complex cosediments with F-actin but does not bind calcium or calmodulin. Our results support a role for the striated muscle dystrophin-glycoprotein complex in linking the actin-based cytoskeleton with the extracellular matrix. Furthermore, our results suggest that dystrophin and dystroglycan may play substantially different functional roles in nonmuscle tissues.

Immuno-electron microscopic localization of calmodulin and calmodulin-binding proteins in the mouse germ cells during spermatogenesis and maturation

When extracts of mouse testis were Western-blotted against a monoclonal antibody which reacts with calmodulin in the presence of Ca2+, all calmodulin was associated with the macromolecules of molecular weight above 50 kDa. Immuno-electron microscopy of testes using this antibody indicated that calmodulin is localized at higher density in the nucleus and cytoplasm of germ cells during the developmental phase between pachytene and round spermatid, showing the highest level just before meiotic divisions. There was no special association of calmodulin to any organelles in these cells. Extremely low levels of calmodulin occurred in spermatogonia and other testicular tissue cells. Calmodulin decreased dramatically as spermatids underwent metamorphosis, becoming detectable only at the perinuclear space of sperm heads. Further relocation to the postacrosomal region occurred during sperm transit to the cauda epididymis. Immunodetection after the calmodulin overlay on ultrathin sections revealed a sharp increase of calmodulin immunogold deposits in the nuclei of spermatids accompanying their condensation. The results indicate that some calmodulin-binding proteins, but not calmodulin itself, accumulate in the nuclei during the final steps of spermiogenesis.

Modulation of the cGMP-gated channel of rod photoreceptor cells by calmodulin

Photobleaching of rhodopsin in rod photoreceptors activates the visual cascade system leading to a decrease in cyclic GMP and the closure of cGMP-gated channels in the rod outer segment plasma membrane. Calcium plays an important role in the recovery of the rod outer segment to its dark state by regulating the resynthesis of cGMP by guanylate cyclase. Here we report that calmodulin, a Ca(2+)-binding protein present in the rod outer segment, increases the apparent Michaelis constant of the channel for cGMP. This results in a decrease in the rate of cation influx into the rod outer segment by two- to sixfold at low cGMP concentrations and has the effect of increasing the sensitivity of the channel to small changes in cGMP levels during phototransduction. Biochemical studies indicate that calcium-calmodulin binds to a protein of M(r) 240K which is tightly associated with the channel. On the basis of these studies, Ca2+ is suggested to play a central role in photorecovery and light adaptation, not only by regulating guanylate cyclase, possibly through recoverin, but also by modulating the cGMP-gated channel through calmodulin interaction with the 240K protein.

Mapping of the immunoreactive domains of a small nuclear ribonucleoprotein-associated Sm-D autoantigen

The Sm-D(D1) small nuclear ribonucleoprotein (snRNP) polypeptide is a major target of autoantibodies diagnostic for systemic lupus erythematosus. The cDNA encoding the protein from Raji cells was expressed in Escherichia coli as a fusion protein with anthranilate synthase (TrpE-Sm-D). When tested by protein blot, the recombinant polypeptide was strongly immunoreactive under defined blotting conditions, which appear to facilitate the refolding of the polypeptide into a native conformation. Multiple translational fusions between the trpE gene and fragments encompassing the length of the Sm-D coding sequence were constructed for epitope mapping. The results describe two general patterns of anti-Sm reactivity: (i) antibodies that recognize only the full-length antigen and are presumably directed against discontinuous epitopes, and (ii) antibodies that recognize the carboxy terminus of the antigen which embodies an extended/charged structure.

Isolation and localization of a spectrin-like protein from echinoderm sperm

Thyone sperm undergo an explosive acrosome reaction resulting in the extension of a 90 microns long acrosomal process. In unreacted sperm, profilamentous actin is sequestered within the profilactin cup (Tilney: Journal of Cell Biology 69:73-89 1976), which consists of four major polypeptides: actin, profilin, and a 250/235 kDa equimolar doublet (TS 250/235). Dialysis of profilactin preparations into an actin assembly buffer resulted in the formation of acrosomal-like macromolecular aggregates containing actin, TS 250/235, and several other polypeptides as detected by SDS-PAGE. TS 250/235 was purified by subjecting extracts of pH solubilized profilactin cups to DEAE and phosphocellulose ion exchange chromatography. TS 250/235 demonstrated immunocrossreactivity with affinity purified polyclonal antibodies raised against S. purpuratus egg spectrin. As determined by biotinylated-calmodulin overlays, both subunits of TS 250/235 bound calmodulin in a Ca(++)-sensitive manner. Electron microscopy of low angle, rotary shadowed replicas of TS 250/235 revealed an elongate rod-shaped molecule with an average contour length of 203 nm. By indirect immunofluorescence, TS 250/235 was found to be uniformly distributed throughout the profilactin cup of the unreacted sperm. This distribution of TS 250/235 correlated with the location of monomeric actin as determined by localization studies utilizing fluorescent-DNase-1. Upon sperm activation, the cellular distribution of TS 250/235 dramatically changed and was observed both along the length and at the base of the extended acrosomal process.

Tyrosine phosphorylation is a signal for the trafficking of pp85, an 85-kDa phosphorylated polypeptide associated with phosphatidylinositol kinase activity

A family of 85/86-kDa (85K/86K) polypeptides closely linked to phosphatidylinositol kinase activity is found in polyoma middle-sized tumor antigen (MTAg)/pp60c-src complexes. MTAg and the 85-kDa phosphoprotein (pp85) could be reassociated in solution, or on blots, after denaturation with SDS. Results from such experiments focus attention on phosphorylation in controlling intracellular sorting and activation of pp85. Tyrosine phosphorylation seems important for recruitment of pp85 from cytosol to membrane. By blotting, pp85 is substantially cytosolic, whereas that recognized by anti-phosphotyrosine antibody is almost exclusively in membranes. Tyrosine phosphorylation also determined association of pp85 with MTAg. Manipulation of MTAg tyrosine phosphorylation, for example, by expressing MTAg using baculovirus vectors in the absence or presence of pp60c-src, dramatically affects reassociation. Finally, tyrosine phosphorylation appears to be involved in release of pp85 from MTAg, since vanadate increased its rate of dissociation.

Calmodulin-binding proteins and calcium/calmodulin-regulated enzyme activities associated with brain actomyosin

Calcium- and calmodulin-regulated ATPase and protein kinase activities are shown to be strongly associated with brain actomyosin. Similar enzymatic activities and an invariable polypeptide profile on sodium dodecyl sulfate-polyacrylamide gel electrophoresis were obtained for brain actomyosin taken through a solubilization-precipitation cycle (1.0-0.1 M KCl), or precipitated from buffers containing 1% Triton X-100 or 10 mM EDTA and 10 mM EGTA. These data suggest a specific complex of brain actomyosin with a protein kinase similar to calmodulin-dependent kinase II, a 190-kDa calmodulin-binding protein (P190), and a calmodulin-like polypeptide. P190 was the major substrate for endogenous calcium-dependent phosphorylation. 125I-Calmodulin overlay technique revealed four major calmodulin-binding polypeptides associated with brain actomyosin: 50- and 60-kDa subunits of the calmodulin-dependent kinase II, P190, and a high molecular weight polypeptide which is probably fodrin. A fraction enriched in P190 had Ca2(+)- and calmodulin-stimulated MgATPase activity, but not myosin-like K-EDTA ATPase activity. The lack of immunological cross-reactivity between brain myosin heavy chain and P190 confirmed that they are distinct molecules.

Use of two-dimensional gel electrophoresis and autoradiography as a tool in cell biology: the example of the thyroid and the liver

Different applications of two-dimensional gel electrophoresis and the research strategies that this methodology allows, with examples drawn from our own work on thyroid and liver cells, are described.

Cyclical differentiation of Trypanosoma brucei involves changes in the cellular complement of calmodulin-binding proteins

The present study was undertaken to evaluate changes in the complement of calmodulin-binding proteins which accompany cyclical differentiation in Trypanosoma brucei. An [125I]trypanosome calmodulin overlay procedure was used to detect calmodulin-binding proteins with Mr of 126,000 and 106,000 that were present in homogenates of slender bloodstream froms but were absent in procyclic culture forms. Competition assays with unlabeled bovine brain or trypanosome calmodulins indicated that the developmentally regulated proteins associated with calmodulins from either source. Moreover, [125I]bovine brain calmodulin associated with the same proteins as trypanosome calmodulin. Homogenates of T. evansi exhibited the same pattern of calmodulin-binding activity as T. brucei slender bloodstream forms; however, T. cruzi and Leishmania tarentolae contained distinct patterns of calmodulin-binding activity. Mouse serum contained no detectable binding proteins while mouse brain contained predominantly proteins of Mr 210,000, 60,000, and 49,000 which were associated with the trypanosome calmodulin probe. The developmentally regulated calmodulin-binding proteins from T. brucei were in the 10,000g pellet. We conclude that the cellular complement of calmodulin-binding proteins varies during the trypanosome life cycle.

Ca2+/calmodulin-dependent protein phosphatase in bovine parotid gland: purification and characterization

Calmodulin-dependent protein phosphatase (CaM-PPase) was isolated from bovine parotid gland by sequential application of DEAE-52, Affi-gel blue and calmodulin-affinity chromatography followed by gel filtration and high performance liquid chromatography. The enzyme was activated in the simultaneous presence of Ni2+ or Mn2+ and Ca2+ plus calmodulin. Ca2+/calmodulin-dependent activation of CaM-PPase was antagonized by inhibitors of calmodulin action, such as W-7 and trifluoperazine. Tryptophan fluorescence was quenched in the presence of Ni2+. CaM-PPase was a heterodimer. The molecular weights of large subunits which bound calmodulin (CaM) were 68 kD and 58 kD - the 68 kD subunit was predominant. Polyclonal antibodies against bovine calcineurin cross-reacted with both types of larger subunits. Using polyclonal antibodies against bovine calcineurin or the monoclonal antibody against subunit B of bovine calcineurin, the smaller molecular weight subunit (19 kD) was found to be immunologically identical to subunit B of bovine calcineurin. In bovine parotid gland, CaM-PPase was found both in acinar and duct cells.

Protein binding to nitrocellulose, nylon and PVDF membranes in immunoassays and electroblotting

A selection of different membranes commonly used to bind proteins in blotting and dot binding assays were investigated for a range of properties which would influence their performance. Large differences were observed in the membranes' ability to bind increasing amounts of protein, the effect of incubation times on the quantity of protein bound and the loss of proteins from the membranes following their incubation with different detergents or protein blocking agents. These differences could only partially explain the observed performance of the membranes when used as protein adsorbants in immunoassays and when different buffers were used for the electro-transfer of several different proteins to a range of membranes.

The cilia of Paramecium tetraurelia contain both Ca2+-dependent and Ca2+-inhibitable calmodulin-binding proteins

To identify protein targets for calmodulin (CaM) in the cilia of Paramecium tetraurelia, we employed a 125I-CaM blot assay after resolution of ciliary proteins on SDS/polyacrylamide gels. Two distinct types of CaM-binding proteins were detected. One group bound 125I-CaM at free Ca2+ concentrations above 0.5-1 microM and included a major binding activity of 63 kDa (C63) and activities of 126 kDa (C126), 96 kDa (C96), and 36 kDa (C36). CaM bound these proteins with high (nanomolar) affinity and specificity relative to related Ca2+ receptors. The second type of protein bound 125I-CaM only when the free Ca2+ concentration was below 1-2 microM and included polypeptides of 95 kDa (E95) and 105 kDa (E105). E105 may also contain Ca2+-dependent binding sites for CaM. Both E95 and E105 exhibited strong specificity for Paramecium CaM over bovine CaM. Ciliary subfractionation experiments suggested that C63, C126, C96, E95, and E105 are bound to the axoneme, whereas C36 is a soluble and/or membrane-associated protein. Additional Ca2+-dependent CaM-binding proteins of 63, 70, and 120 kDa were found associated with ciliary membrane vesicles. In support of these results, filtration binding assays also indicated high-affinity binding sites for CaM on isolated intact axonemes and suggested the presence of both Ca2+-dependent and Ca2+-inhibitable targets. Like E95 and E105, the Ca2+-inhibitable CaM-binding sites showed strong preference for Paramecium CaM over vertebrate CaM and troponin C. Together, these results suggest that CaM has multiple targets in the cilium and hence may regulate ciliary motility in a complex and pleiotropic fashion.

Calcium-dependent calmodulin-binding proteins associated with mammalian DNA polymerase alpha

Complex, multiprotein forms of bovine (calf thymus), hamster (Chinese hamster ovary cell), and human (HeLa) cell DNA polymerase alpha (Pol alpha) were analyzed for their content of calmodulin-binding proteins. The approach used an established autoradiographic technique employing 125I-labeled calmodulin to probe proteins in denaturing SDS-polyacrylamide gel electropherograms. All three Pol alpha enzymes were associated with discrete, Ca2+-dependent calmodulin-binding proteins. Conventionally purified calf thymus Pol alpha holoenzyme contained three prominent, trifluoperazine-sensitive species with apparent molecular masses of approx. 120, 80 and 48 kDa. The 120 and 48 kDa species remained associated with the polymerase.primase core of the calf enzyme during immunopurification with monoclonal antibodies directed specifically against the polymerase subunit. The patterns of the calmodulin-binding proteins displayed by conventionally purified preparations of hamster and human Pol alpha enzymes were similar to each other and distinctly different from the pattern of comparable preparations of calf thymus Pol alpha. Immunopurified preparations of the human and hamster Pol alphas retained significant calmodulin-binding activity of apparent molecular masses of approx. 55, 80 and 150-200 kDa.

Calmodulin-binding proteins in chromaffin cell plasma membranes

Calmodulin-binding proteins present in chromaffin cell plasma membranes were isolated and directly compared with calmodulin-binding proteins present in chromaffin granule membranes. Chromaffin cell plasma membranes were prepared using Cytodex 1 microcarriers. Marker enzyme studies on this preparation showed a nine- to 10-fold plasma membrane enrichment over cell homogenates and a low contamination of these plasma membranes by subcellular organelles. Plasma membranes prepared in this manner were solubilized with Triton X-100 and applied to a calmodulin-affinity column in the presence of calcium. Several major calmodulin-binding proteins (240, 105, and 65 kilodaltons) were eluted by an EGTA-containing buffer. 125I-Calmodulin overlay experiments on nitrocellulose sheets containing both chromaffin plasma and granule membranes showed that these two membranes have several calmodulin-binding proteins in common (65, 60, 53, and 50 kilodaltons), as well as unique calmodulin-binding proteins (34 kilodaltons in granule membranes and 240 and 160 kilodaltons in plasma membranes). The 65-kilodalton calmodulin-binding protein present in both membrane types was shown to consist of two isoforms (pI 6.0 and 6.2) by two-dimensional gel electrophoresis. Previous experiments from our laboratory, using two monoclonal antibodies (mAb 30 and mAb 48) specific for a rat brain synaptic vesicle membrane protein (p65), showed that the monoclonal antibodies reacted with a 65-kilodalton calmodulin-binding protein present in at least three neurosecretory vesicles (chromaffin granules, neurohypophyseal granules, and rat brain synaptic vesicles). When these monoclonal antibodies were tested on chromaffin cell plasma membranes and calmodulin-binding proteins isolated from these membranes, they recognized a 65-kilodalton protein. These results indicate that an immunologically identical calmodulin-binding protein is expressed in both chromaffin granule membranes (as well as other secretory vesicle membranes) and chromaffin cell plasma membranes, thus suggesting a possible role for this protein in granule/plasma membrane interaction.

Restoration of antibody binding to blotted meningococcal outer membrane proteins using various detergents

Restoration of IgG antibody binding to heat-denatured meningococcal outer membrane proteins has been studied on immunoblots with a series of 14 detergents. Nitrocellulose strips with the blotted proteins were incubated with the detergents and sera from human volunteers vaccinated with meningococcal membrane proteins. Zwitterionic and ionic detergents, containing substituted quarternary ammonium or amino groups with a minimum of 10 C atoms in the alkyl chain, restored the antigenicity of the serotype-specific class 2 porin protein. The concentrations of the Zwittergent detergents necessary for activation decreased with increasing alkyl chain length of the homologues. Only zwitterionic detergents renatured the class 1 protein. Both proteins were weakly antigenic in the presence of the nonionic detergents Triton X-100 and Tween 20. Meningococcal lipopolysaccharide restored antibody binding to the porin, but not to the class 1 protein. Similar concentrations of lipopolysaccharides from two other gram-negative bacteria had no effect.

Expression of brush border calmodulin-binding proteins during human small and large bowel differentiation

The expression and immunocytochemical localization of three brush border cytoskeletal calmodulin-binding proteins, caldesmon, fodrin, and the 110 kDa subunit of the 110 kDa calmodulin complex, have been studied in human intestinal epithelial cells as a function of their ontogenic differentiation. At immature stages (fetal week 8), caldesmon and fodrin were present in undifferentiated intestinal epithelial cells. However, no 110 kDa protein was detectable except a 135 kDa immunoreactive species. The 110 kDa form appeared at week 12, when microvilli differentiate, and became prominent at week 14 simultaneously with the disappearance of the 135 kDa species. Finally at week 14, the calmodulin-binding protein pattern was identical to that found in adults. Immunocytochemical experiments revealed that at week 8, antibodies to caldesmon and fodrin gave a fluorescence lining at the periphery of the cells, whereas the 110 kDa immunoreactive species was hardly detectable. Then, as early as week 12 of gestation, with the three antisera, a bright fluorescence lined the apex of the cells, as in adults. In the colon, the events were delayed. This study demonstrates that the developmental pattern of the three calmodulin-binding proteins investigated, caldesmon, fodrin and the 110 kDa subunit, parallels the temporal differentiation of human intestinal brush borders and the proximo-distal morphological intestinal maturation.

Calmodulin in normal and cystic fibrosis human intestine at different developmental stages

Calmodulin concentrations and localisation have been analysed as a function of development in human intestinal epithelial cells from normal and cystic fibrosis individuals. In normal fetuses up to eight weeks of gestation intestinal epithelial cells which were still undifferentiated were not immunoreactive and their calmodulin content was low. From eight weeks onwards there was a significant overall increase in calmodulin content concomitant with its segregation to the apical side of epithelial cells. At 14 weeks of gestation calmodulin concentrations and localisation closely resembled those of adults. The developmental pattern of calmodulin appeared to parallel the morphological and functional maturation of brush borders which occurs during the first trimester of pregnancy. In the intestinal epithelial cells from a 19 weeks cystic fibrosis fetus and a cystic fibrosis newborn infant neither calmodulin concentration, nor its localisation were affected. Similarly, brush border calmodulin binding proteins and enzymatic activities were similar in normal subjects and the cystic fibrosis intestine.

Calmodulin-dependent multifunctional protein kinase in Aspergillus nidulans

A Ca2+/calmodulin (CaM)-dependent multifunctional protein kinase has been isolated from Aspergillus nidulans and purified to homogeneity. Unlike any CaM-dependent multifunctional protein kinase described previously, the native enzyme from Aspergillus behaves as a monomer. The calculated molecular weight is 41,200. NaDodSO4/PAGE reveals a single protein band with an apparent Mr of 51,000. Two-dimensional isoelectric focusing/NaDodSO4/PAGE of the purified enzyme showed one major and one minor more acidic Coomassie blue-stained spot, both of which bind 125I-labeled calmodulin in a calcium-dependent manner. The kinase is autophosphorylated in a calcium- and CaM-dependent manner, yielding an increase in the amount and number of more acidic forms of the enzyme. The Aspergillus kinase catalyzes the Ca2+/CaM-dependent phosphorylation of known substrates of type II Ca2+/CaM-dependent protein kinases, including glycogen synthase, microtubule-associated protein 2, synapsin, tubulin, gizzard myosin light chain, and casein. Cross-reactivity between antiserum raised against native rat brain protein kinase II and 125I-labeled Aspergillus kinase has been detected. Two forms of CaM have been isolated from Aspergillus nidulans, both of which activate the Aspergillus kinase at lower concentrations than that required for activation by bovine brain CaM.

Characterization of calmodulin-binding components in the pituitary gonadotrope

We have used an 125I-calmodulin gel overlayer assay to identify calmodulin-binding component in the rat pituitary. Tissue-specific and Ca2+ -dependent patterns of 125I-calmodulin binding were observed, with five major Ca2+-dependent 125I-calmodulin-labeled components of subunit Mr greater than 205,000, 200,000, 135,000, 60,000, and 52,000. Ca2+-dependent binding was defined as that which was abolished in the presence of 1 mM EGTA. Calmodulin binding was inhibited by calmodulin antagonists such as penfluridol (1 microM) or pimozide (1 microM). Some Ca2+-independent binding was observed and appears to be due to (nonspecific) hydrophobic interaction of calmodulin with acid-soluble proteins, principally histones. Subcellular fractionation revealed that the Ca2+-dependent calmodulin-binding components are localized primarily in the cytosolic fraction. Separation of dispersed anterior pituitary cells by a linear metrizamide gradient yielded gonadotrope-enriched fractions; these contained all five 125I-calmodulin-binding components corresponding to the major bands in the pituitary homogenate. Studies with ovariectomized and steroid-replaced animals indicated that the tissue content of calmodulin-binding components, like those of calmodulin itself, did not appear to be differentially regulated by steroids. A comparison of rat and bovine pituitary tissue homogenates revealed that binding components migrating at the same apparent Mrs were found for four of the components (the largest component is lacking in the bovine system).

Spectrin and calmodulin in spreading mouse blastomeres

The role of spectrin and its association with calmodulin in spreading mouse blastomeres was investigated. Embryonic spectrin binds 125I-calmodulin in a calcium-dependent fashion in the blot overlay technique. Double-labeling experiments show coordinate redistribution of spectrin and calmodulin in blastomeres preparing to undergo active spreading movement. At this stage cortical spectrin staining is lost from the region of cell-substrate contact and spectrin and calmodulin become concentrated in two structures closely associated with the contacted region: a group of spherical bodies located on the cytoplasmic side of the cortical layer and a subcortical ring that marks the perimeter of the contacted region. The localization pattern of spectrin and calmodulin is also coordinated with that of actin and myosin. The results suggest that spectrin plays a role in the spreading of blastomeres and that this function may involve linkage of spectrin, calmodulin, and the cortical contractile apparatus.

Developmental pattern of calmodulin-binding proteins in rat jejunal epithelial cells

Calmodulin-binding proteins have been studied in presumptive rat jejunal epithelial cells and in purified rat brush borders during development. Incubation of nitrocellulose replicas with [125I] calmodulin revealed that, at immature stages (13-15 days of fetal life), only two calmodulin-binding bands were detectable with molecular masses of approximately 145,000 and 135,000 daltons. By fetal day 19, additional calmodulin-binding proteins of 240,000 and 110,000 daltons were observed. The 145,000- and 240,000-dalton calmodulin-binding bands contained polypeptides that were immunologically similar to caldesmon and to the alpha-subunit of the non-erythroid spectrin (fodrin) respectively. Antisera reactive with the 110K subunit of the microvillus 110K-calmodulin complex labelled a 135,000-dalton band which comigrated with one of the calmodulin-binding proteins. This 135,000-dalton immunoreactive polypeptide persisted until birth but was absent in brush borders isolated from adult intestine. In addition, the 110K antisera reacted with an approximately 110,000-dalton subunit by fetal day 19. At birth, numerous lower-molecular-mass 110K immunoreactive bands were also detectable. Immunocytochemical localization of the three calmodulin-binding proteins revealed that, at fetal day 14, caldesmon and fodrin displayed fluorescence lining the periphery of the epithelial cells, whereas staining with the 110K antisera was very weak. At fetal day 19, staining with the three antisera resulted in bright fluorescence localized in the apical part of the epithelial cells, in parallel to the differentiation of brush borders. At this stage, the apical staining of the calmodulin-binding proteins was similar to that of the adult.(ABSTRACT TRUNCATED AT 250 WORDS)

Drosophilia spectrin. I. Characterization of the purified protein

We purified a protein from Drosophila S3 tissue culture cells that has many of the diagnostic features of spectrin from vertebrate organisms: (a) The protein consists of two equimolar subunits (Mr = 234 and 226 kD) that can be reversibly cross-linked into a complex composed of equal amounts of the two subunits. (b) Electron microscopy of the native molecule reveals two intertwined, elongated strands with a contour length of 180 nm. (c) Antibodies directed against vertebrate spectrin react with the Drosophila protein and, similarly, antibodies to the Drosophila protein react with vertebrate spectrins. One monoclonal antibody has been found to react with both of the Drosophila subunits and with both subunits of vertebrate brain spectrin. (d) The Drosophila protein exhibits both actin-binding and calcium-dependent calmodulin-binding activities. Based on the above criteria, this protein appears to be a bona fide member of the spectrin family of proteins.

Reaction of monoclonal antibodies with plasma membrane proteins after binding on nitrocellulose: renaturation of antigenic sites and reduction of nonspecific antibody binding

The immunochemical reaction of monoclonal antibodies directed against native membrane proteins was investigated after their separation in sodium dodecyl sulfate polyacrylamide gels and electrotransfer to nitrocellulose. Nonspecific binding of antibodies to membrane proteins, which was increased by beta-mercaptoethanol treatment or heat denaturation of the antibodies, could be significantly reduced if 1 M D-glucose plus 10% (v/v) glycerol was added during the incubation with the antibodies. It was found that specific antibody binding was drastically reduced by SDS treatment of the membrane proteins. During the electrotransfer to nitrocellulose and the simultaneous removal of SDS, some increase in antibody binding was observed. Considerable renaturation of antigenic sites in the blotted proteins could be induced if the nitrocellulose blots were incubated for 16 h at 37 degrees C in phosphate-buffered saline. With the introduction of both modifications, the renaturation step, and the addition of D-glucose and glycerol to reduce nonspecific antibody binding, the immunoblot technique may be successfully applied to detect conformational antibodies against membrane proteins.

Identification of a fodrin-like protein in rat liver basolateral membranes

A 240 KDa calmodulin- and actin-binding protein has been identified in the plasma membrane of rat liver. This protein is mainly associated with subplasmamembrane fractions enriched in the basolateral domain and very little of it is found in the canalicular membrane fraction. An 80 KDa actin-binding protein is found only in the canalicular fraction.

Bordetella pertussis adenylate cyclase: isolation and purification by calmodulin-sepharose 4B chromatography

Purified preparations of adenylate cyclase were obtained from crude urea extracts of Bordetella pertussis by a one-step calmodulin affinity chromatography technique. Diluted extract was loaded onto the column and washed, and adenylate cyclase was eluted with 10mM EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]. A 104-fold purification was accomplished in one step. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the affinity-purified adenylate cyclase was dissociated into one major protein band with an apparent molecular weight of 60,000 and a minor band at 200,000. The affinity-purified adenylate cyclase was observed to have adenylate cyclase enzymatic activity which was activated by calmodulin, to bind 125I-calmodulin, and to be free of pertussis toxin as determined by in vivo and in vitro assays.

Activation of the multifunctional Ca2+/calmodulin-dependent protein kinase by autophosphorylation: ATP modulates production of an autonomous enzyme

The multifunctional Ca2+/calmodulin-dependent protein kinase purified from rat brain cytosol undergoes an intramolecular self-phosphorylation or autophosphorylation. Autophosphorylation produces two strikingly different effects on kinase activity that are dependent on the level of ATP used in the reaction. At low but saturating levels of ATP (5 microM), autophosphorylation causes a 75% reduction in kinase activity, with the residual activity still retaining a dependence on Ca2+ and calmodulin. By contrast, at high but physiological levels of ATP (500 microM), the kinase is converted by autophosphorylation to a form that is autonomous of Ca2+ and calmodulin, with no accompanying reduction in activity. The extent of phosphate incorporation does not determine whether the kinase becomes inhibited or autonomous. Autophosphorylated kinase shows the functional change characteristic of the ATP concentration used during the reaction--inhibited at low ATP and autonomous at high ATP--even when compared at the same level of incorporated phosphate. ATP appears to regulate the site(s) phosphorylated during activation of the kinase and thereby modulates the dual effects of autophosphorylation. Events triggered by transient elevations of cellular Ca2+ may be potentiated and retained by generation of the Ca2+/calmodulin-independent protein kinase activity.

Enhancement of immunoblot sensitivity by heating of hydrated filters

Immunoblots of either dot or Western type were exposed to heat before reaction with antibody. Dramatic increases in immunoblot sensitivity were seen for certain antigen-antibody pairs after heating of either dry or hydrated nitrocellulose filters at or above 100 degrees C. Heating of filters in the hydrated state improved the linearity of immunodetection and produced the highest signal-to-noise ratio. This treatment greatly increased immunoblot sensitivity with several peptide-generated antibodies, whereas decreased sensitivity was seen with antibodies against native proteins. Heating of hydrated filters after antigen immobilization is thus a potentially powerful way to increase the sensitivity of immunoblot analysis for antibodies that preferentially recognize epitopes in denatured proteins.

Sequential immunostaining (gold/silver) and complete protein staining (AuroDye) on Western blots

A double staining method is described which combines immunodetection with sensitive staining of the complete electropherogram on the same membrane. The method is based on the use of Tween 20 as blocking agent, and uses immunogold/silver staining of specific antigens and gold staining of the overall protein pattern with AuroDye. This double staining makes possible the exact location of an immunodetected band within a complex protein pattern.

Analysis of serum insulin-like growth factor binding proteins using western blotting: use of the method for titration of the binding proteins and competitive binding studies

A nitrocellulose gel transfer technique has been adapted to study the insulin-like growth factor (IGF) binding proteins of human serum. Normal and hypopituitary sera were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by electroblotting to nitrocellulose or nylon membrane. Nonidet-P40 (3%) and Tween 20 (0.1%) were required for quenching and to allow detection of the IGF binding proteins by autoradiography after overlay with either 125I-labeled IGF I or IGF II. Several forms of IGF binding protein have been identified with molecular weights of 41,500, 38,500, 34,000, 30,000, and 24,000. Titration and competitive binding studies with IGF were performed on the transferred IGF binding proteins, indicating that binding proteins isolated by this technique can be characterized.

The interaction of calmodulin with rat liver plasma membrane

Rat liver plasma membranes contain relatively high amounts of EGTA-insensitive calmodulin which seems to interact with cytoskeletal proteins. Calmodulin is particularly enriched in a subplasmamembrane fraction containing basolateral membranes. Two calmodulin-binding proteins with apparent Mr of 240 KDa and 145 KDa have been found associated with the purified plasmamembranes.

Autophosphorylation of calmodulin kinase II: functional aspects

Autophosphorylation of purified calmodulin kinase II dramatically inhibited protein kinase activity and enhanced substrate selectivity. Inhibition was observed over a wide range of calmodulin concentrations but calmodulin binding was unaffected. Autophosphorylation of calmodulin kinase II may be a mechanism for limiting phosphorylation to physiological substrates and terminating some of calcium's actions in synaptic events.