人源性基因calsenilin/KChIP3/DREAM的单克隆抗体的制备及鉴定

Calsenilin/KChIP3/DREAM, 是脑中高表达蛋白,最初发现是因其与presenilin 和钙离子结合而得名。作为转录因子抑制因子,该基因在细胞核内具有多种功能。该基因在钙离子作用下细胞核内常常与c-fos、prodynorphin等基因的启动子下游的特异性DRE位点相结合,调节这些基因的表达。另一方面,作为钾离子通道结合蛋白,该基因具有4种isoforms,其中KChIP1广泛存在于各种组织中而KChIP2只在心脏中特异表达,KChIP3和 KChIP4则在脑中显示较高的表达。4种基因在C-端结构非常相象,N-端则显示多样性。除此之外,和许多基因相似,calsenilin经PKC、CKI、PKA等激酶作用可产生多位点的磷酸化,其中主要位点Ser63的磷酸化可以阻止caspase-3对该基因的降解作用。另一方面,Calsenilin作为转录因子激动因子结合于维生素D和视黄酸效应因子启动子上游促进转录的进行。 到目前为止,Calsenilin/KChIP3/DREAM在细胞核内具有双重基因表达调控作用,即当结合于启动子上游时显示正调控而当结合在启动子下游时显示负调控。为了更加深入研究calsenilin的功能及寻找新的受其调控的基因,首先制备可特异性识别的单克隆抗体。利用RT-PCR 技术,从人脑中提取RNA扩增calsenilin全基因,克隆于pGEX-4T-2原核细胞表达载体中,经IPTG诱导表达、Gluthathion Sepharose 4B纯化得到GST-calsenilin/DREAM/KChIP3重组蛋白,并免疫小鼠。通过PEG细胞融合得到单克隆抗体。经细胞免疫染色及Western blotting检测显示说明本实验得到单克隆抗体可以用来进行细胞免疫染色及Western blotting等检测。该抗体的成功制备,为今后对calsenilin/DREAM/KChIP3调控基因表达的更深入研究提供了有效工具,也填补了国内尚无该基因单克隆抗体资源的空白。     

The Potassium Channel Interacting Protein 3 (DREAM/KChIP3) Heterodimerizes with and Regulates Calmodulin Function

Downstream regulatory element antagonistic modulator (DREAM/KChIP3), a neuronal EF-hand protein, modulates pain, potassium channel activity, and binds presenilin 1. Using affinity capture of neuronal proteins by immobilized DREAM/KChIP3 in the presence and absence of calcium (Ca²⁺) followed by mass spectroscopic identification of interacting proteins, we demonstrate that in the presence of Ca²⁺, DREAM/KChIP3 interacts with the EF-hand protein, calmodulin (CaM). The interaction of DREAM/KChIP3 with CaM does not occur in the absence of Ca²⁺. In the absence of Ca²⁺, DREAM/KChIP3 binds the EF-hand protein, calcineurin subunit-B. Ca²⁺-bound DREAM/KChIP3 binds CaM with a dissociation constant of ∼3 μm as assessed by changes in DREAM/KChIP3 intrinsic protein fluorescence in the presence of CaM. Two-dimensional ¹H,¹⁵N heteronuclear single quantum coherence spectra reveal changes in chemical shifts and line broadening upon the addition of CaM to ¹⁵N DREAM/KChIP3. The amino-terminal portion of DREAM/KChIP3 is required for its binding to CaM because a construct of DREAM/KChIP3 lacking the first 94 amino-terminal residues fails to bind CaM as assessed by fluorescence spectroscopy. The addition of Ca²⁺-bound DREAM/KChIP3 increases the activation of calcineurin (CN) by calcium CaM. A DREAM/KChIP3 mutant incapable of binding Ca²⁺ also stimulates calmodulin-dependent CN activity. The shortened form of DREAM/KChIP3 lacking the NH₂-terminal amino acids fails to activate CN in the presence of calcium CaM. Our data demonstrate the interaction of DREAM/KChIP3 with the important EF-hand protein, CaM, and show that the interaction alters CN activity.     

Observations on the binding of lanthanides and calcium to vitamin D-dependent chick intestinal calcium-binding protein. Implications regarding calcium-binding protein function

The binding of calcium and terbium to purified chick vitamin D-dependent intestinal calcium-binding protein was studied by terbium fluorescence, circular dichroism, and intrinsic protein fluorescence techniques. Calcium-binding protein bound, with high affinity, at least 3 mol of terbium/mol of protein; numerous low affinity terbium-binding sites were also noted. The three highest affinity sites were resolved into one very high affinity site (site A) and two other sites (sites B and C) with slightly lower affinity. Resonance energy transfer from tryptophan residues to terbium occurred only with site A. This site was filled before sites B and C. Competition experiments in which calcium was used to displace terbium bound to the protein showed that larger amounts of calcium were needed to displace terbium from site A than from sites B and C. Energy transfer from terbium to holmium indicated that the terbium-binding sites (B and C) were located close to each other (about 7-12 A) but were distant (greater than 12 A) from site A. The addition of EDTA to calcium-binding protein resulted in a 25% decrease in intrinsic protein fluorescence, suggesting a conformational change in the protein. The titration of EDTA-treated calcium-binding protein with calcium resulted in recovery of intrinsic protein fluorescence. A reversible calcium-dependent change in the ellipticity of calcium-binding protein in circular dichroism experiments was also seen. These observed properties suggest that vitamin D-dependent chick intestinal calcium-binding protein behaves in a manner similar to other well-known calcium-binding regulatory proteins.     

Ions binding to S100 proteins. I. Calcium- and zinc-binding properties of bovine brain S100 alpha alpha, S100a (alpha beta), and S100b (beta beta) protein: Zn2+ regulates Ca2+ binding on S100b protein

Flow dialysis measurements of calcium binding to bovine brain S100 alpha alpha, S100a (alpha beta), and S100b (beta beta) proteins in 20 mM Tris-HCl buffer at pH 7.5 and 8.3 revealed that S100 proteins bind specifically 4 Ca2+ eq/mol of protein dimer. The specific calcium-binding sites had, therefore, been assigned to typical amino acid sequences on the alpha and beta subunit. The protein affinity for calcium is much lower in the presence of magnesium and potassium. Potassium strongly antagonizes calcium binding on two calcium-binding sites responsible for most of the Ca2+-induced conformational changes on S100 proteins (probably site II alpha and site II beta). Zinc-binding studies in the absence of divalent cations revealed eight zinc-binding sites/mol of S100b protein dimer that we assumed to correspond to 4 zinc-binding sites/beta subunit. Zinc binding to S100b studied with UV spectroscopy methods showed that the occupation of the four higher affinity sites and the four lower affinity sites on the protein dimer were responsible for different conformational changes in S100b structure. Zinc binding on the higher affinity sites regulates calcium binding to S100b by increasing the protein affinity for calcium and decreasing the antagonistic effect of potassium on calcium binding. Zinc-binding studies on S100a and S100 alpha alpha protein showed that the Trp-containing S100 proteins bind zinc more weakly than S100b protein. Calcium-binding studies on zinc-bound S100a proved that calcium- and zinc-binding sites were distinct although there was no increase in zinc-bound S100a affinity for calcium, as in S100b protein. Finally we provide evidence that discrepancies between previously published results on the optical properties of S100b protein probably result from oxidation of the sulfhydryl groups in the protein.     

DREAM-alphaCREM interaction via leucine-charged domains derepresses downstream regulatory element-dependent transcription

Protein kinase A-dependent derepression of the human prodynorphin gene is regulated by the differential occupancy of the Dyn downstream regulatory element (DRE) site. Here, we show that a direct protein-protein interaction between DREAM and the CREM repressor isoform, alphaCREM, prevents binding of DREAM to the DRE and suggests a mechanism for cyclic AMP-dependent derepression of the prodynorphin gene in human neuroblastoma cells. Phosphorylation in the kinase-inducible domain of alphaCREM is not required for the interaction, but phospho-alphaCREM shows higher affinity for DREAM. The interaction with alphaCREM is independent of the Ca(2+)-binding properties of DREAM and is governed by leucine-charged residue-rich domains located in both alphaCREM and DREAM. Thus, our results propose a new mechanism for DREAM-mediated derepression that can operate independently of changes in nuclear Ca(2+).     

The vanadate complex of the calcium-transport ATPase of the sarcoplasmic reticulum, its formation and dissociation

Vanadate binding to different sarcoplasmic reticulum membrane preparations was determined by measuring bound vanadate colorimetrically and by phosphorylating the vanadate-free enzyme fraction with [gamma-32P] ATP. Colorimetry allowed the study of the dependence of equilibrium vanadate binding on ionized magnesium and the displacing effect of ionized calcium at vanadate concentrations greater than 0.1 mM only. At saturating magnesium concentration the enzyme binds 6-8 nmol vanadate/mg protein and half-maximum saturation is reached at 40 microM. Vanadate is displaced from the enzyme when its high-affinity calcium-binding sites are saturated and conversely calcium is solely displaced from its high-affinity binding sites by vanadate. The phosphorylation procedure allowed the measurement of equilibrium binding as well as the kinetics of vanadate binding and release at vanadate concentrations below 0.1 mM. Half-times of 30s and 3s were observed for vanadate release induced by 0.1 mM and 1 mM calcium respectively. Millimolar concentrations of ATP are required for vanadate displacement. Under equilibrium conditions the enzyme displays an affinity for vanadate of 1.6 X 10(6) M-1. The dependence on the concentration of vanadate of the rate of vanadate binding yielded an affinity of only 1 X 10(4) M-1. Closed vesicles bind vanadate much more slowly than calcium-permeable preparations. The initial rate of calcium-induced vanadate dissociation is accelerated considerably when the vesicles are made calcium permeable. The rate of vanadate dissociation from calcium-permeable vesicles reaches half-maximum values at 1-2 mM calcium indicating that the internal low-affinity calcium-binding sites must first be occupied in order to release bound vanadate. The results suggest that vanadate binding leads to a transition of the external high to internal low-affinity calcium-binding sites.     

Divalent cation-nucleotide complex at the exchangeable nucleotide binding site of tubulin

Tubulin was first treated with alkaline phosphatase-agarose to vacate the exchangeable nucleotide binding site and then tested for manganese binding sites by Mn(II) EPR. Buttlaire et al. ((1980) J. Biol. Chem. 255, 2164-2168) have shown that high affinity manganese binding occurs at a single site normally occupied by magnesium. We report that the number of high affinity manganese binding sites per mol of tubulin depends on the number of occupied exchangeable nucleotide binding sites. Thus, removal of nucleotides results in a loss of high affinity manganese binding sites. The EPR spectra of manganese bound to tubulin and to GTP are found to be qualitatively similar. These data indicate that high affinity manganese binding is the result of the formation of a metal-nucleotide complex at the exchangeable nucleotide binding site. In addition it was found that zinc, cobalt, and magnesium bind with approximately equal affinity to this site whereas calcium binds only weakly.     

Maximal serum stimulation of the c-fos serum response element requires both the serum response factor and a novel binding factor, SRE-binding protein.

We have previously reported on the presence of a CArG motif at -100 in the Rous sarcoma virus long terminal repeat which binds an avian nuclear protein termed enhancer factor III (EFIII) (A. Boulden and L. Sealy, Virology 174:204-216, 1990). By all analyses, EFIII protein appears to be the avian homolog of the serum response factor (SRF). In this study, we identify a second CArG motif (EFIIIB) in the Rous sarcoma virus long terminal repeat enhancer at -162 and show only slightly lower binding affinity of the EFIII/SRF protein for this element in comparison with c-fos serum response element (SRE) and EFIII DNAs. Although all three elements bind the SRF with similar affinities, serum induction mediated by the c-fos SRE greatly exceeds that effected by the EFIII or EFIIIB sequence. We postulated that this difference in serum inducibility might result from binding of factors other than the SRF which occurs on the c-fos SRE but not on EFIII and EFIIIB sequences. Upon closer inspection of nuclear proteins which bind the c-fos SRE in chicken embryo fibroblast and NIH 3T3 nuclear extracts, we discovered another binding factor, SRE-binding protein (SRE BP), which fails to recognize EFIII DNA with high affinity. Competition analyses, methylation interference, and site-directed mutagenesis have determined that the SRE BP binding element overlaps and lies immediately 3' to the CArG box of the c-fos SRE. Mutation of the c-fos SRE so that it no longer binds SRE BP reduces serum inducibility to 33% of the wild-type level. Conversely, mutation of the EFIII sequence so that it binds SRE BP with high affinity results in a 400% increase in serum induction, with maximal stimulation equaling that of the c-fos SRE. We conclude that binding of both SRE BP and SRF is required for maximal serum induction. The SRE BP binding site coincides with the recently reported binding site for rNF-IL6 on the c-fos SRE. Nonetheless, we show that SRE BP is distinct from rNF-IL6, and identification of this novel factor is being pursued.     

Metal-binding studies for a de novo designed calcium-binding protein

To understand the key determinants in calcium-binding affinity, a calcium-binding site with pentagonal bipyramid geometry was designed into a non-calcium-binding protein, domain 1 of CD2. This metal-binding protein has five mutations with a net charge in the coordination sphere of -5 and is termed DEEEE. Fluorescence resonance energy transfer was used to determine the metal-binding affinity of DEEEE to the calcium analog terbium. The addition of protein concentration to Tb(III) solution results in a large enhancement of Tb(III) fluorescence due to energy transfer between terbium ions and aromatic residues in CD2-D1. In addition, both calcium and lanthanum compete with terbium for the same desired metal binding pocket. Our designed protein exhibits a stronger affinity for Tb(III), with a K(d) of 21 microM, than natural calcium-binding proteins with a similar Greek key scaffold.