Isolation and characterization of recoverin-like Ca(2+)-binding protein from rat brain

Recoverin antibody-associated late-onset ataxia without retinopathy

Acquired cerebellar ataxia is a rare, in many cases immune-modulated and paraneoplastic illness. Acute and slowly progredient processes are possible. An early treatment is important for a good clinical outcome. Here we present the case of female patient in her 60s with an antirecoverin associated cerebellitis without retinopathia and neoplasia. After an immunosuppressive therapy with steroids and rituximab the symptoms improved, and the progression could be stopped.

Cloning and expression of the gene for a novel protein from Mycobacterium smegmatis with functional similarity to eukaryotic calmodulin

A calmodulin-like protein (CAMLP) from Mycobacterium smegmatis was purified to homogeneity and partially sequenced; these data were used to produce a full-length clone, whose DNA sequence contained a 55-amino-acid open reading frame. M. smegmatis CAMLP, expressed in Escherichia coli, exhibited properties characteristic of eukaryotic calmodulin: calcium-dependent stimulation of eukaryotic phosphodiesterase, which was inhibited by the calmodulin antagonist trifluoperazine, and reaction with anti-bovine brain calmodulin antibodies. Consistent with the presence of nine acidic amino acids (16%) in M. smegmatis CAMLP, there is one putative calcium-binding domain in this CAMLP, compared to four such domains for eukaryotic calmodulin, reflecting the smaller molecular size (approximately 6 kDa) of M. smegmatis CAMLP. Ultracentrifugation and mass spectral studies excluded the possibility that calcium promotes oligomerization of purified M. smegmatis CAMLP.

Calcium-regulated DNA binding and oligomerization of the neuronal calcium-sensing protein, calsenilin/DREAM/KChIP3

Calsenilin/DREAM/KChIP3, a member of the recoverin branch of the EF-hand superfamily, interacts with presenilins, serves as a calcium-regulated transcriptional repressor, and interacts with A-type potassium channels. Here we report physicochemical characterization of calcium binding, oligomerization, and DNA binding of human calsenilin/DREAM/KChIP3. Equilibrium Ca(2+) binding measurements indicate that the protein binds 3 Ca(2+) with a dissociation constant of 14 microM and a Hill coefficient of 0.7. Dynamic light scattering and size exclusion chromatography show that the Ca(2+)-bound protein exists as a dimer at protein concentrations lower than 150 microM and forms a tetramer at concentrations above 200 microM. The Ca(2+)-free protein is a tetramer in the concentration range 20-450 microM. Isothermal titration calorimetry and dynamic light scattering indicate that the Ca(2+)-free protein tetramer binds endothermically (DeltaH = +25 kcal/mol) to four molecules of DNA derived from the downstream regulatory element (DRE) of either the prodynorphin or c-fos genes. One DRE molecule binds tightly to the protein with a dissociation constant (K(d)) of 75 nM, and the other three bind more weakly (K(d) = 640 nM). No significant DNA binding was observed for the Ca(2+)-bound protein. The N-terminal protein fragment (residues 1-70) binds nonspecifically to DRE in a Ca(2+)-independent manner, whereas a C-terminal fragment containing the four EF-hands (residues 65-256) binds DRE (K(d) = 200 nM) in a Ca(2+)-regulated and sequence-specific fashion. The C-terminal fragment is a tetramer in the Ca(2+)-free state and dissociates into dimers at saturating Ca(2+) levels.

Age-related changes in expression of hippocalcin and NVP2 in rat brain

Expression of hippocalcin and neural visinin-like calcium-binding protein 2 (NVP2) in aging rat brain was investigated by immunoblot and immunohistochemical analyses. In 3-month old rats, hippocalcin and NVP2 were present at high concentrations in hippocampal and cerebral pyramidal cells and dentate granule cells, with hippocalcin protein levels being five to ten times higher than NVP2 levels. Hippocalcin levels in hippocampus and cerebral cortex decreased by approximately 20% at 24 months. While the number of hippocalcin-positive cells in CA3, dentate gyrus and cerebral cortex were preserved, staining intensity decreased. In contrast, the number and staining intensity of hippocalcin-positive cells in CA1 were maintained. NVP2 levels in hippocampus and cerebral cortex decreased by approximately 30% at 24 months. In cerebral cortex, the number and intensity of NVP2-positive cells decreased. In CA1 through CA3 and in dentate gyrus, NVP2-positive cell numbers were preserved, but staining intensity decreased. In summary, the loss of hippocalcin and NVP2 in aging rat brain may be associated with age-related impairment of postsynaptic functions.

The development of neural visinin-like Ca(2+)-binding protein 2 immunoreactivity in the rat neocortex and hippocampus

Neural visinin-like Ca(2+)-binding protein 2 (NVP2) immunoreactivity in the rat neocortex and hippocampus was barely detectable by immunoblot analysis on postnatal day 1 (P1), but increased during postnatal weeks 2-3, reaching a plateau on P28. Immunohistochemical analysis revealed moderate immunoreactivity firstly on P7 in some subsets of the hippocampal interneurons and in the hippocampal pyramidal cells and dentate granule cells. Immunoreactivity of the interneurons decreased during postnatal weeks 2-3 and disappeared by P28. In contrast, immunoreactivity of the cortical and hippocampal pyramidal cells and dentate granule cells abruptly increased during postnatal week 2. The distinctly immunoreactive cells were distributed throughout the neocortex, especially in the cortical plate, and the stratum pyramidale of Ammon's horn and granular layer of the dentate gyrus on P14. Immunoreactivity was homogeneously concentrated in the cell bodies and proximal dendrites at this stage, whereas thereafter immunoreactivity in the neuropil gradually increased, and underwent a relative decrease in the cell bodies. By P28, the higher and granular immunoreactivity in the neuropil covered whole layers of the neocortex, Ammon's horn and the dentate gyrus, the same as in adults. Differential expression of NVP2 in different neuron populations may reflect the differential functional consequences for neuronal development.

Distribution pattern of three neural calcium-binding proteins (NCS-1, VILIP and recoverin) in chicken, bovine and rat retina

Neural Ca(2+)-binding proteins (NCaPs) constitute a subfamily of 4-EF-hand proteins, and display a histological and structural dichotomy: the A-type NCaPs are selectively expressed by the retina and pineal organ and display two canonical EF-hands, whereas the B-type NCaPs are found in the entire brain and present three regular EF-hands. In this study, antisera were raised against the A-type NCaP recoverin (26 kDa) and the B-type NCaPs VILIP and NCS-1 (22 kDa). Since the sequence identity among NCaPs is high, specific polyclonal antibodies were purified by double cross-immunoaffinity chromatography; both ELISA and immunoblot analyses determined that the resulting antibodies showed selectivity ratios inferior to 1/363 for the two other related NCaPs. Besides, the anti-VILIP antibodies displayed some affinity toward neurocalcin delta, and the antirecoverin antibodies recognized a 24 kDa protein, which is most likely visinin. Thus, immunohistochemical studies on the chicken, rat and cow retina revealed that anti-recoverin antibodies recognized the vertebrate photoreceptors and a small number of mammalian bipolar cells. Anti-VILIP antibodies exclusively labelled the inner retina, i.e. the amacrine and ganglion cells. NCS-1 was mainly present in the photoreceptor inner segments, the inner plexiform layer and the ganglion cells. NCS-1 showed the highest species disparity. The retinal localization of NCS-1 and VILIP offered an important morphological basis for the understanding of their function. Furthermore, specific antibodies against the NCaPs may enable the identification of cell populations in more complex neural tissues, such as the brain.

Expression of hippocalcin in the developing rat brain

Expression of hippocalcin in the developing rat brain was investigated by a combination of Northern blot, in situ hybridization, immunoblot and immunohistochemical methods. In the hippocampus, hippocalcin mRNA and immunoreactivity first appeared in the CA3 pyramidal cells on embryonic day 19 (E19) and postnatal day 1 (P1), respectively, and extended throughout Ammon's horn. After P14, the hippocampal pyramidal cells, especially in the CA1 region, maintained the highest expression level among the brain regions. The dentate granule cells expressed a small amount of hippocalcin mRNA and immunoreactivity from P7 and maintained a low level through the developmental stages. In the cerebral cortex, hippocalcin mRNA and immunoreactivity appeared in the pyramidal cells of the piriform cortex from P1 and P4, respectively. Their expression extended throughout the cerebral cortex and reached the maximum level on P14, and then declined gradually with age to half of the maximum level by adults. In the cerebellum, a few Purkinje cells expressed a small amount of hippocalcin mRNA and immunoreactivity on P7. Their expression became evident in most of the Purkinje cells on P14 and increased gradually by P28. Then, their expression declined with age; however, the immunoreactivity was concentrated in the cell bodies and proximal segments of the dendrites in adults. These results suggest that the expression of hippocalcin mRNA and protein is strictly controlled by both the cell type and the developmental process and that hippocalcin plays a role in neuronal differentiation in the early stages of development and may relate to other neuronal function in the adult brain.

Immunohistochemical localization of neural visinin-like Ca(2+)-binding protein 2 in adult rat brain

The distribution of neural visinin-like Ca(2+)-binding protein 2 (NVP2) in adult rat brain was analyzed by immunoblot and immunohistochemical methods. NVP2 immunoreactivity was expressed intensely in the pyramidal cells of the CA1 and 2 regions of Ammon's horn, the granule cells of the dentate gyrus and the pyramidal cells of the cerebral cortex layers II to VI, moderately in the pyramidal-shaped cells of the anterior olfactory nucleus and large spindle-shaped cells of the globus pallidus, and weakly in neurons in the nucleus accumbens and the anterior and dorsomedial thalamus. In most cell types, NVP2 immunoreactivity was located in the cytoplasm and plasma membrane of the cell bodies and dendrites.

Hippocalcin: a calcium-binding protein of the EF-hand superfamily dominantly expressed in the hippocampus

Hippocalcin is a recently identified Ca(2+)-binding protein with three EF-hand structures, dominantly expressed in the hippocampal pyramidal layer. The complete amino acid sequence of hippocalcin deduced from the cDNA is composed of 195 residues, has a calculated molecular mass of 22,574 daltons, and has a striking sequence homology to those of visinin, recoverin, S-modulin, neurocalcins and neural visinin-like proteins. Hippocalcin binds 3 mol of Ca2+ per mol of protein at submicromolar Ca2+ levels, and associates the plasma membrane in a Ca(2+)-dependent manner. Hippocalcin is myristoylated at its NH2-terminal glycine residue, and this modification is a key event in terms of its membrane-association property.

Molecular cloning of two additional members of the neural visinin-like Ca(2+)-binding protein gene family

We have isolated a rat cDNA clone encoding a neural visinin-like Ca(2+)-binding protein (NVP), which we designate NVP-1. To identify additional molecular forms of NVP, a rat brain cDNA library was screened for their presence using an NVP-1 cDNA probe under low-stringency hybridization conditions. Two types of cDNA clones encoding structurally related proteins, designated NVP-2 and NVP-3, have been isolated. The deduced amino acid sequences of NVP-2 and NVP-3 are 89.0% and 68.6% identical to that of NVP-1, respectively, and contain consensus sequences for EF-hand Ca(2+)-binding sites. Northern blot analysis shows that NVP-1, NVP-2, and NVP-3 mRNAs are most highly expressed in brain and are differentially expressed in various regions of rat brain. These results suggest that NVP-2 and NVP-3 are additional members of the NVP gene family.

Distribution of hippocalcin mRNA and immunoreactivity in rat brain

Distribution of hippocalcin in rat brain was analysed by in situ hybridization and immunohistochemical methods. Hippocalcin mRNA and immunoreactivity were expressed more intensely in the pyramidal cells of the hippocampus, intensely in the Purkinje cells of the cerebellum, moderately in the dentate granule cells and pyramidal cells of cerebral cortex layers II-VI and weakly in the large neuronal cells of the caudate-putamen. Some discrepancies in the localization of hippocalcin mRNA and immunoreactivity were noted in the mamillary nuclei, anterior part of the thalamus and the septal nuclei. In most cell types, hippocalcin immunoreactivity was localized in the cytoplasm and plasma membrane of cell bodies and dendrites.

The effect of recoverin-like calcium-binding proteins on the photoresponse of retinal rods

The rod photoresponse is triggered by an enzyme cascade that stimulates cGMP hydrolysis. The resulting fall in cGMP leads to a decrease in Ca2+, which promotes photoresponse recovery by activating guanylate cyclase, causing cGMP resynthesis. In vitro biochemical studies suggest that Ca2+ activation of guanylate cyclase is medicated by recoverin, a 26 kd Ca(2+)-binding protein. To evaluate this, exogenous bovine recoverin and two other homologous Ca(2+)-binding proteins from chicken and Gecko retina were dialyzed into functionally intact Gecko rods using whole-cell recording. All three proteins prolonged the rising phase of the photoresponse without affecting the kinetics of response recovery. These results suggest that recoverin-like proteins affect termination of the transduction cascade, rather than mediate Ca(2+)-sensitive activation of guanylate cyclase.

Neurocalcin family: a novel calcium-binding protein abundant in bovine central nervous system

We purified and sequenced from bovine brain a novel calcium-binding protein. This protein which we named neurocalcin has 3 putative EF hand motifs and a close homology with recoverin which activates guanylate cyclase Ca2+ dependently. Neurocalcin has at least 6 isoforms and is expressed in the central nervous system (CNS), retina and adrenal gland. Considering unique distribution of neurocalcin, this protein may an important physiological role which differs from that of visinin or recoverin.

Calcium-myristoyl protein switch

Recoverin, a recently discovered member of the EF-hand superfamily of Ca(2+)-binding proteins, serves as a Ca2+ sensor in vision. The amino terminus of the protein from retinal rod cells contains a covalently attached myristoyl or related N-acyl group. We report here studies of unmyristoylated and myristoylated recombinant recoverin designed to delineate the biological role of this hydrophobic unit. Ca2+ induces the binding of both the unmyristoylated and myristoylated proteins to phenyl-agarose, a hydrophobic support. Binding was half-maximal at 1.1 and 1.0 microM Ca2+, respectively. The Hill coefficients of 1.8 and 1.7, respectively, indicate that binding was cooperative. In contrast, Ca2+ induced the binding of myristoylated but not of unmyristoylated recoverin to rod outer segment membranes. Binding to these membranes was half-maximal at 2.1 microM Ca2+, and the Hill coefficient was 2.4. Likewise, myristoylated but not unmyristoylated recoverin exhibited Ca(2+)-induced binding to phosphatidylcholine vesicles. These findings suggest that the binding of Ca2+ to recoverin has two effects: (i) hydrophobic surfaces are exposed, allowing the protein to interact with complementary nonpolar sites, such as the aromatic rings of phenyl-agarose; and (ii) the myristoyl group is extruded, enabling recoverin to insert into a lipid bilayer membrane. The myristoyl group is likely to be an active participant in Ca2+ signaling by recoverin and related EF-hand proteins such as visinin and neurocalcin.

Molecular cloning of hippocalcin, a novel calcium-binding protein of the recoverin family exclusively expressed in hippocampus

We have isolated a cDNA clone encoding a novel calcium-binding protein of the recoverin family from rat brain cDNA library. This clone (PCB11) has 588 nucleotides in the open reading frame including the termination codon, 174 nucleotides of the 5' leader and 800 nucleotides of the 3' noncoding region. The complete amino acid sequence deduced from the cDNA is composed of 195 residues, has a calculated molecular mass of 22,574 Daltons, and contains three putative calcium-binding domains of the EF-hand structure. The deduced amino acid sequence has a striking sequence homology to those of the retinal recoverin family (recoverin, visinin, P26, 23kD protein, S-modulin) and the brain-derived recoverin family (P23k, 21-kDa CaBP and neurocalcin). Northern blot, in situ hybridization, immunoblot and immunohistochemical analyses revealed that the protein is exclusively expressed in pyramidal layer of the hippocampus. The protein was therefore designated hippocalcin.