Tyrosine nitration of voltage-dependent anion channels in cardiac ischemia-reperfusion: reduction by peroxynitrite scavenging

Excess superoxide (O(2)(-)) and nitric oxide (NO) forms peroxynitrite (ONOO(-)) during cardiac ischemia reperfusion (IR) injury, which in turn induces protein tyrosine nitration (tyr-N). Mitochondria are both a source of and target for ONOO(-). Our aim was to identify specific mitochondrial proteins that display enhanced tyr-N after cardiac IR injury, and to explore whether inhibiting O(2)(-)/ONOO(-) during IR decreases mitochondrial protein tyr-N and consequently improves cardiac function. We show here that IR increased tyr-N of 35 and 15kDa mitochondrial proteins using Western blot analysis with 3-nitrotyrosine antibody. Immunoprecipitation (IP) followed by LC-MS/MS identified 13 protein candidates for tyr-N. IP and Western blot identified and confirmed that the 35kDa tyr-N protein is the voltage-dependent anion channel (VDAC). Tyr-N of native cardiac VDAC with IR was verified on recombinant (r) VDAC with exogenous ONOO(-). We also found that ONOO(-) directly enhanced rVDAC channel activity, and rVDAC tyr-N induced by ONOO(-) formed oligomers. Resveratrol (RES), a scavenger of O(2)(-)/ONOO(-), reduced the tyr-N levels of both native and recombinant VDAC, while L-NAME, which inhibits NO generation, only reduced tyr-N levels of native VDAC. O(2)(-) and ONOO(-) levels were reduced in perfused hearts during IR by RES and L-NAME and this was accompanied by improved cardiac function. These results identify tyr-N of VDAC and show that reducing ONOO(-) during cardiac IR injury can attenuate tyr-N of VDAC and improve cardiac function.

Proteomic analysis of articular cartilage vesicles from normal and osteoarthritic cartilage

OBJECTIVE

Articular cartilage vesicles (ACVs) are extracellular organelles found in normal articular cartilage. While they were initially defined by their ability to generate pathologic calcium crystals in cartilage of osteoarthritis (OA) patients, they can also alter the phenotype of normal chondrocytes through the transfer of RNA and protein. The purpose of this study was to analyze the proteome of ACVs from normal and OA human cartilage.

METHODS

ACVs were isolated from cartilage samples from 10 normal controls and 10 OA patients. We identified the ACV proteomes using in-gel trypsin digestion, nanospray liquid chromatography tandem mass spectrometry analysis of tryptic peptides, followed by searching an appropriate subset of the Uniprot database. We further differentiated between normal and OA ACVs by Holm-Sidak analysis for multiple comparison testing.

RESULTS

More than 1,700 proteins were identified in ACVs. Approximately 170 proteins satisfied our stringent criteria of having >1 representative peptide per protein present, and a false discovery rate of ≤5%. These proteins included extracellular matrix components, phospholipid binding proteins, enzymes, and cytoskeletal components, including actin. While few proteins were seen exclusively in normal or OA ACVs, immunoglobulins and complement components were present only in OA ACVs. Compared to normal ACVs, OA ACVs displayed decreases in matrix proteoglycans and increases in transforming growth factor β-induced protein βig-H3, DEL-1, vitronectin, and serine protease HtrA1 (P < 0.01).

CONCLUSION

These findings lend support to the concept of ACVs as physiologic structures in articular cartilage. Changes in OA ACVs are largely quantitative and reflect an altered matrix and the presence of inflammation, rather than revealing fundamental changes in composition.

Identification of differentially expressed proteins in the aqueous humor of primary congenital glaucoma

Primary Congenital Glaucoma (PCG) is an autosomal recessive disease caused by an abnormal development of the anterior chamber angle. Although, PCG has been linked to several genetic loci, the role that the genes at these loci or their encoded proteins play in the pathophysiology of PCG and development of the anterior chamber is not known. To identify proteins that may be altered in PCG and that may help in understanding the underlying pathophysiology of the disease, we took a global proteomics approach. Tryptic digests of the complex mixtures of proteins in aqueous humor were analyzed using Liquid Chromatography/Mass Spectrometry (LC-MS/MS). Proteins were identified by searching the data against the human subset of the UniProt database. The proteomes of aqueous humor in PCG (n = 7) and patients undergoing cataract surgery as control (n = 4) were compared based on the scan counts of comparable proteins. Using stringent filtering criteria, Apolipoprotein A-IV (APOA-IV), Albumin and Antithrombin 3 (ANT3) were detected at significantly higher levels in PCG AH compared to control, whereas Transthyretin (TTR), Prostaglandin-H2 D-isomerase (PTGDS), Opticin (OPT) and Interphotoreceptor Retinoid Binding Protein (IRBP) were detected at significantly lower levels. Many of these proteins play a role in retinoic acid (RA) binding/transport and have been implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's (AD). It is possible that similar to AD, the pathologic changes in PCG during development could be influenced by the availability of RA in the anterior chamber.

Abstract 44: STAT1-dependent expression of genes and proteins involved in energy metabolism links tumor growth and radioresistance to the Warburg effect and predicts poor prognosis in cancer patients

Signal Transducer and Activator of Transcription 1 (STAT1) has traditionally been regarded as a transmitter of interferon signaling and a pro-apoptotic tumor suppressor. Recent data have identified new functions of STAT1 associated with tumorigenesis and resistance to genotoxic stress, including ionizing radiation (IR) and chemotherapy. To investigate the mechanisms contributing to the tumorigenic functions of STAT1, we performed a combined transcriptomic-proteomic expressional analysis of tumor xenografts with stable Stat1 knock-down (KD) relative to tumors with wild type (wt) Stat1. We also compared previously described SCC61 and nu61 isologous tumors, where SCC61 is radiosensitive and nu61 is radioresistant counterparts with different expression of IFN/Stat1 pathway. Transcriptional profiling was based on Affymetrix Human GeneChip® Gene 1.0 ST microarrays. Proteomes were determined from the MS/MS data by searching against the human subset of the UniProt database. Knockdown of STAT1 led to significant growth suppression in untreated tumors and radiosensitization of irradiated tumors. These changes were accompanied by alterations in the expression of genes and proteins of glycolysis/gluconeogenesis (GG), the citrate cycle (CC), and oxidative phosphorylation (OP). Of these pathways, GG had the most concordant changes in gene and protein expression and demonstrated a STAT1-dependent expression of genes and proteins consistent with tumor-specific glycolysis. IR drastically suppressed the GG pathway in STAT1 KD tumors without significant change in STAT1 WT tumors. Using 18F-FDG-PET we observed significantly higher glucose uptake in nu61 compared to SCC61 post-irradiation (6Gy). The STAT1 and glycolytic pathways were co-expressed in human breast tumors, and expression of STAT1-linked glycolytic genes was highly predictive of poor prognosis. Our results identify a previously uncharacterized function of STAT1 in tumors: expressional regulation of genes and enzymes involved in glycolysis, the citrate cycle, and mitochondrial oxidative phosphorylation, with predominant regulation of glycolysis. STAT1-dependent transcriptional and translational regulation of glycolysis suggests a potential role for STAT1 as a transcriptional modulator of genes responsible for the Warburg effect.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 44.

The urine proteome for radiation biodosimetry: effect of total body vs. local kidney irradiation

Victims of nuclear accidents or radiological terrorism are likely to receive varying doses of ionizing radiation inhomogeneously distributed over the body. Early biomarkers may be useful in determining organ-specific doses due to total body irradiation (TBI) or partial body irradiation. The authors used liquid chromatography and mass spectrometry to compare the effect of TBI and local kidney irradiation (LKI) on the rat urine proteome using a single 10-Gy dose of x-rays. Both TBI and LKI altered the urinary protein profile within 24 h with noticeable differences in gene ontology categories. Some proteins, including fetuin-B, tissue kallikrein, beta-glucuronidase, vitamin D-dependent calcium binding protein and chondroitin sulfate proteoglycan NG2, were detected only in the TBI group. Some other proteins, including major urinary protein-1, RNA binding protein 19, neuron navigator, Dapper homolog 3, WD repeat and FYVE domain containing protein 3, sorting nexin-8, ankycorbin and aquaporin were detected only in the LKI group. Protease inhibitors and kidney proteins were more abundant (fraction of total scans) in the LKI group. Urine protein (Up) and creatinine (Uc) (Up/Uc) ratios and urinary albumin abundance decreased in both TBI and LKI groups. Several markers of acute kidney injury were not detectable in either irradiated group. Present data indicate that abundance and number of proteins may follow opposite trends. These novel findings demonstrate intriguing differences between TBI and LKI, and suggest that urine proteome may be useful in determining organ-specific changes caused by partial body irradiation.

STAT1-dependent expression of energy metabolic pathways links tumour growth and radioresistance to the Warburg effect

BACKGROUND

The Signal Transducer and Activator of Transcription 1 (STAT1) has traditionally been regarded as a transmitter of interferon signaling and a pro-apoptotic tumour suppressor. Recent data have identified new functions of STAT1 associated with tumourigenesis and resistance to genotoxic stress, including ionizing radiation (IR) and chemotherapy. To investigate the mechanisms contributing to the tumourigenic functions of STAT1, we performed a combined transcriptomic-proteomic expressional analysis and found that STAT1 is associated with regulation of energy metabolism with potential implication in the Warburg effect.

METHODS

We generated a stable knockdown of STAT1 in the SCC61 human squamous cell carcinoma cell line, established tumour xenografts in athymic mice, and compared transcriptomic and proteomic profiles of STAT1 wild-type (WT) and knockdown (KD) untreated or irradiated (IR) tumours. Transcriptional profiling was based on Affymetrix Human GeneChip(R) Gene 1.0 ST microarrays. Proteomes were determined from the tandem mass spectrometry (MS/MS) data by searching against the human subset of the UniProt database. Data were analysed using Significance Analysis of Microarrays for ribonucleic acid and Visualize software for proteins. Functional analysis was performed with Ingenuity Pathway Analysis with statistical significance measured by Fisher's exact test.

RESULTS

Knockdown of STAT1 led to significant growth suppression in untreated tumours and radio sensitization of irradiated tumours. These changes were accompanied by alterations in the expression of genes and proteins of glycolysis/gluconeogenesis (GG), the citrate cycle (CC) and oxidative phosphorylation (OP). Of these pathways, GG had the most concordant changes in gene and protein expression and demonstrated a STAT1-dependent expression of genes and proteins consistent with tumour-specific glycolysis. In addition, IR drastically suppressed the GG pathway in STAT1 KD tumours without significant change in STAT1 WT tumours.

CONCLUSION

Our results identify a previously uncharacterized function of STAT1 in tumours: expressional regulation of genes encoding proteins involved in glycolysis, the citrate cycle and mitochondrial oxidative phosphorylation, with predominant regulation of glycolytic genes. STAT1-dependent expressional regulation of glycolysis suggests a potential role for STAT1 as a transcriptional modulator of genes responsible for the Warburg effect.

Comparative proteomic analysis of PAI-1 and TNF-alpha-derived endothelial microparticles

Endothelium-derived microparticles (EMPs) are small vesicles released from endothelial cells in response to cell injury, apoptosis, or activation. Elevated concentrations of EMPs have been associated with many inflammatory and vascular diseases. EMPs also mediate long range signaling and alter downstream cell function. Unfortunately, the molecular and cellular basis of microparticle production and downstream cell function is poorly understood. We hypothesize that EMPs generated by different agonists will produce distinct populations of EMPs with unique protein compositions. To test this hypothesis, different EMP populations were generated from human umbilical vein endothelial cells by stimulation with plasminogen activator inhibitor type 1 (PAI-1) or tumor necrosis factor-alpha (TNF-alpha) and subjected to proteomic analysis by LC/MS. We identified 432 common proteins in all EMP populations studied. Also identified were 231 proteins unique to control EMPs, 104 proteins unique to PAI-1 EMPs and 70 proteins unique to TNF-alpha EMPs. Interestingly, variations in protein abundance were found among many of the common EMP proteins, suggesting that differences exist between EMPs on a relative scale. Finally, gene ontology (GO) and KEGG pathway analysis revealed many functional similarities and few differences between the EMP populations studied. In summary, our results clearly indicate that EMPs generated by PAI-1 and TNF-alpha produce EMPs with overlapping but distinct protein compositions. These observations provide fundamental insight into the mechanisms regulating the production of these particles and their physiological role in numerous diseases.

The Urine Proteome as a Biomarker of Radiation Injury: Submitted to Proteomics- Clinical Applications Special Issue: "Renal and Urinary Proteomics (Thongboonkerd)"

Terrorist attacks or nuclear accidents could expose large numbers of people to ionizing radiation, and early biomarkers of radiation injury would be critical for triage, treatment and follow-up of such individuals. However, no such biomarkers have yet been proven to exist. We tested the potential of high throughput proteomics to identify protein biomarkers of radiation injury after total body X-ray irradiation in a rat model. Subtle functional changes in the kidney are suggested by an increased glomerular permeability for macromolecules measured within 24 hours after TBI. Ultrastructural changes in glomerular podocytes include partial loss of the interdigitating organization of foot processes. Analysis of urine by LC-MS/MS and 2D-GE showed significant changes in the urine proteome within 24 hours after TBI. Tissue kallikrein 1-related peptidase, cysteine proteinase inhibitor cystatin C and oxidized histidine were found to be increased while a number of proteinase inhibitors including kallikrein-binding protein and albumin were found to be decreased post-irradiation. Thus, TBI causes immediately detectable changes in renal structure and function and in the urinary protein profile. This suggests that both systemic and renal changes are induced by radiation and it may be possible to identify a set of biomarkers unique to radiation injury.

Pseudomonas aeruginosa ExoS ADP-ribosyltransferase inhibits ERM phosphorylation

Pseudomonas aeruginosa causes life-threatening infections in compromised and cystic fibrosis patients. Pathogenesis stems from a number of virulence factors, including four type III translocated cytotoxins: ExoS, ExoT, ExoY and ExoU. ExoS is a bifunctional toxin: the N terminus (amino acids 96-219) encodes a Rho GTPase Activating Protein (GAP) domain. The C terminus (amino acids 234-453) encodes a 14-3-3-dependent ADP-ribosyltransferase domain which transfers ADP-ribose from NAD onto substrates such as the Ras GTPases and vimentin. Ezrin/radixin/moesin (ERM) proteins have recently been identified as high-affinity substrates for ADP-ribosylation by ExoS. Expression of ExoS in HeLa cells led to a loss of phosphorylation of ERM proteins that was dependent upon the expression of ADP-ribosyltransferase activity. MALDI-MS and site-directed mutagenesis studies determined that ExoS ADP-ribosylated moesin at three C-terminal arginines (Arg553, Arg560 and Arg563), which cluster Thr558, the site of phosphorylation by protein kinase C and Rho kinase. ADP-ribosylated-moesin was a poor target for phosphorylation by protein kinase C and Rho kinase, which showed that ADP-ribosylation directly inhibited ERM phosphorylation. Expression of dominant active-moesin inhibited cell rounding elicited by ExoS, indicating that moesin is a physiological target in cultured cells. This is the first demonstration that a bacterial toxin inhibits the phosphorylation of a mammalian protein through ADP-ribosylation. These data explain how the expression of the ADP-ribosylation of ExoS modifies the actin cytoskeleton and indicate that ExoS possesses redundant enzymatic activities to depolymerize the actin cytoskeleton.

The serine protease inhibitor trappin-2 is present in cartilage and synovial fluid in osteoarthritis

OBJECTIVE

Trappins are small serine protease inhibitors bound to extracellular matrix (ECM) through the actions of transglutaminase (TGase) enzymes. Trappin-2 is present in many tissues and is upregulated at sites of injury. In osteoarthritis (OA), serine proteases contribute to articular cartilage destruction, and TGase activity is increased. Yet little is known about matrix-bound serine protease inhibitors or TGase substrates in articular cartilage. Our purpose was to determine if trappin-2 was present in OA cartilage and synovial fluid (SF).

METHODS

OA knee articular cartilage and SF were assayed for trappin-2 protein by Western blotting, ELISA, and immunohistochemistry. Trappin-2 mRNA was detected with RT-PCR. The ECM components bound to trappin-2 were identified by 2-D gel electrophoresis and peptide fingerprinting.

RESULTS

Trappin-2 was detectable in OA articular cartilage extracts, cultured chondrocytes, conditioned media, and SF by Western blotting. OA cartilage protein extracts contained significantly higher quantities of trappin-2 than normal cartilage protein extracts (22.98 +/- 1.28 ng/mg wet weight vs 14.97 +/- 1.92 ng/mg wet weight; p < 0.01). RT-PCR confirmed the presence of trappin-2 mRNA in OA chondrocytes. Immunohistochemical studies of OA cartilage revealed trappin-2 protein in chondrocytes. Peptide mapping of trappin-2 binding partners showed that fibromodulin was bound to trappin-2 in cartilage.

CONCLUSION

We confirmed the presence of trappin-2 in OA cartilage and SF. Elevated levels of TGase activity in OA cartilage may increase levels of this serine protease inhibitor in response to injury.

Stimulation of a Ca(2+)-calmodulin-activated histone 3 arginine kinase in quiescent rat heart endothelial cells compared to actively dividing cells

A Ca(2+)-calmodulin-activated histone 3 kinase was partially purified from nuclear extracts of dividing and quiescent rat heart endothelial cells. The histone 3 phosphorylating activity was 20-100-fold higher in quiescent than in dividing cells. Base hydrolysis followed by amino acid analysis revealed that histone 3 was phosphorylated on arginine. Further investigations were conducted to determine whether phosphorylation of histone 3 also occurred in vivo. Cells were incubated for 3 h in a phosphate-free medium supplemented with [32P]phosphoric acid. It was observed that the nuclear content of arginine-phosphorylated histone 3 was considerably higher in quiescent than in dividing rat heart endothelial cells. The histone 3 arginine kinase is a component of a complex containing a Ca(2+)-dependent calmodulin-binding protein of apparent molecular mass of 85 kDa. Using polyclonal antibodies to an 85-kDa protein, also the major Ca(2+)-dependent calmodulin-binding component of the histone 3 arginine kinase from calf thymus, an immunoreactive protein of identical apparent molecular mass was found to be present in equal amounts both in dividing and quiescent cells. We propose that the 85-kDa protein is either the histone 3 arginine kinase or one of its subunits and that phosphorylation of histone 3 is involved with cell cycle exit in eukaryotes.

Ca(2+)-calmodulin-dependent phosphorylation of arginine in histone 3 by a nuclear kinase from mouse leukemia cells

A Ca(2+)-calmodulin dependent histone 3 kinase was partially purified from a low salt (150 mM NaCl) nuclear extract of mouse leukemia cells by calmodulin-Sepharose affinity chromatography. In vitro, the kinase activity transferred gamma-phosphate from ATP to histone 3 to form an acid-labile and alkaline-stable linkage. Under the assay conditions 1.8 mol of phosphate are incorporated per mol of histone 3. Upon modification of arginine residues with phenylglyoxal prior to phosphorylation, a considerable decrease in the amount of phosphate transferred to histone 3 was observed. Amino acid analysis revealed that H3 was phosphorylated on arginine residues. To identify the phosphorylated peptide(s), histone 3 was cleaved with cyanogen bromide prior to phosphorylation. The phosphorylated mixture was then separated by gel filtration high-performance liquid chromatography under denaturing conditions. Fragments I (N-terminal 10.3-kDa peptide) and III (C-terminal 1.7-kDa peptide) were both phosphorylated. Amino acid sequencing further revealed that the molar yields of 3 of the 4 arginines present in the phosphorylated cyanogen bromide fragment III were reduced by a factor of about 10 compared with the corresponding arginines from the unphosphorylated fragment. In the case of fragment I, 25 cycles of Edman degradation revealed that the recovery of only arginine 2 was reduced by a factor of 20. The putative phosphorylation sites are arginines 2, 128, 129, and 131. The sequence information offered an indirect evidence that these arginines were the sites of phosphorylation. The kinase described in this report represents a first member of a potentially important new class of kinases which are Ca(2+)-calmodulin dependent and which phosphorylate arginine.

Asparaginyl deamidation-methylation of rat ventricular myosin light chains

Spontaneous asparaginyl deamidation can produce damage to cytoskeletal proteins, and may lead to their targeting for subsequent rapid intracellular breakdown or repair. To test if myofibrillar proteins are subject to spontaneous deamidation damage in vitro, purified rat ventricular myosin light chain 1 (MLC1v) and phosphorylatable myosin light chain 2 (MPLC2v) were incubated (37 degrees C, 4 h, pH 2-11), and tested as substrates for human erythrocyte and rat cardiac protein carboxyl methyltransferase (PCMT). PCMT catalyzes the transfer of a methyl group from [3H-methyl] S-adenosyl methionine to deamidated asparaginyl residues and altered aspartyl residues on damaged proteins. MLC1v and MPLC2v underwent extensive incubation damage at neutral and alkaline pH. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography revealed 3H-incorporation into MLC1v, MPLC2v, and a Mr = 14,000 polypeptide. 3H-methylated, CNBr-cleavage fragments of PCMT-methylated light chains were then separated by reverse-phase high performance liquid chromatography, and sequenced by automated Edman degradation. The major 3H-labeled peptide of the Mr = 14,000 protein proved homologous to residues 84 to 104 of rat MPLC2v, with a proposed deamidation site at Asn99-Ala100. The major 3H-labeled peptide from MLC1v proved homologous to residues 73 to 111 of rat cardiac MLC1v, with a proposed deamidation site at Asn108-Ser109. These results indicate that both myofibrillar protein subunits undergo selective non-enzymatic degradation at neutral and alkaline pH, resulting in the formation of methyl acceptor sites for human erythrocyte and rat cardiac PCMT. PCMT-catalyzed methylation of ventricular myosin light chains may be important in the repair, or subsequent proteolysis of these long-lived structural proteins of the myofibril.

In vivo collagen turnover during development of thyroxine-induced left ventricular hypertrophy

Cardiac fibroblasts synthesize large amounts of procollagens, yet only a small fraction of mature collagens accumulate in the extracellular matrix. To determine the roles of intracellular degradation of newly synthesized procollagens and extracellular degradation of mature collagens during normal growth and during thyroxine-induced left ventricular hypertrophy, in vivo left ventricular procollagen synthetic rates were assessed in control rats and rats treated with L-thyroxine for 1, 2, 4, and 8 wk (1 mg.kg-1.day-1). A modification of the flooding infusion method was developed using measurements of cardiac prolyl-tRNA, and tissue-free and protein-bound hydroxyproline specific radioactivities 60 min after intravenous administration of a massive dose of [3H]proline. Degradative rates of newly synthesized procollagens and mature collagens were then derived as the difference between rates of procollagen synthesis and collagen accumulation. Left ventricular procollagen synthetic rates were markedly increased after 1 wk of hormone administration (256 +/- 16 and 166 +/- 13 micrograms/day per left ventricle for thyroxine-treated and control animals, respectively; P less than 0.01). An even greater increase in procollagen synthetic rates was observed after 8 wk (438 +/- 46 and 202 +/- 18 micrograms/day for thyroxine-treated and control animals, respectively; P less than 0.01). Despite increased procollagen synthesis, disproportionate accumulation of fibrillar collagens (assessed as the relative concentration of protein-bound hydroxyproline in left ventricular tissue) did not occur. Derived left ventricular degradative rates for newly synthesized procollagens as well as for mature collagens were increased in thyroxine-treated animals. Increased procollagen synthesis, enhanced flux of newly synthesized procollagens through intracellular degradative pathways, and extensive extracellular matrix remodeling without disproportionate collagen accumulation are characteristics of this form of "physiological" left ventricular hypertrophy.

Identification and partial purification of a chromatin bound calmodulin activated histone 3 kinase from calf thymus

A calcium-calmodulin (Ca2(+)-CaM) stimulated histone H3 phosphorylating activity was identified as a component of a nuclear protein complex purified from a 150 mM NaCl extract of calf thymus chromatin. This activity bound to a CaM-Sepharose affinity column in a Ca2+ dependent manner and was eluted off the column in the presence of EGTA. Equilibrium centrifugation of the EGTA eluate on a sucrose density gradient revealed that the activity is a component of a larger complex identified at 25% sucrose. This complex consisted of two major proteins, having Mr of 65 and 75 kDa. Using [125I] CaM and the gel overlay technique it was shown that the 75 kDa protein is the major CaM binding protein in the complex.

Identification and characterization of the calmodulin-binding domain of neuromodulin, a neurospecific calmodulin-binding protein

Neuromodulin (formerly designated P-57) is an abundant, neural specific, calmodulin-binding protein which exhibits higher affinity for calmodulin in the absence of free Ca2+ than in the presence of free Ca2+. In this study a series of proteolytic fragments of neuromodulin were systematically screened for calmodulin-Sepharose binding activity. A 9-amino acid fragment, designated M1-C1 and having the sequence RGHITRKKL, was identified as the putative CaM-binding domain of neuromodulin. Two heptadecapeptides, designated FP57-Phe and FP57-Trp, were synthesized, each containing the M1-C1 sequence and the four flanking amino acids from each site. The FP57-Trp peptide contained a tryptophan residue in place of the native phenylalanine. Anti-FP57-Phe antibody binding to neuromodulin was inhibited by preincubation of antibodies with excess FP57-Phe. 125I-CaM gel overlay of neuromodulin was inhibited by anti-FP57-Phe antibodies. Addition of CaM to FP57-Trp increased peptide tryptophanyl fluorescence. In the presence of Ca2+, the stoichiometry of the FP57-Trp.CaM complex was 1:1, FP57-Trp binding to CaM was competitive with neuromodulin. The Ca2+-independent dissociation constant of the FP57-Phe.CaM complex was 0.41 microM. The Ca2+-dependent affinity of the complex could not be measured directly but appeared to be significantly greater than the Ca2+-independent affinity.

Amino acid sequence of P-57, a neurospecific calmodulin-binding protein

The amino acid sequence was determined for bovine brain P-57, a neurospecific, membrane-associated, calmodulin-binding protein. It consists of a single 239-residue polypeptide chain blocked at its amino terminus and containing an unusually hydrophilic amino acid composition. Seventy percent of the molecule is composed of Glu/Gln, Ala, Lys, Asp/Asn, and Pro; there is only one aromatic residue. A lack of favorable cleavage sites required that a particularly wide variety of digests and subdigests be performed to obtain appropriate sets of overlapping peptides. This protein is clearly homologous with the cDNA-derived sequence of mouse brain P-57, although the bovine protein is 12 amino acid residues longer; the homology is less obvious in the middle sections of the two sequences. Bovine brain P-57 lacks homology with any other protein in an updated sequence database. A segment reported to interact with calmodulin (Arg-Gly-His-Ile-Thr-Arg-Lys-Lys-Leu) is placed at residues 43-51 within the only extended segment of P-57 that carries the net positive charge that would favor that interaction. There is no hydrophobic segment characteristic of many proteins that interact with membranes.

Characterization of murine cDNAs encoding P-57, a neural-specific calmodulin-binding protein

Polyclonal antibodies raised against bovine brain P-57, a neural-specific calmodulin-binding protein, were used to isolate murine cDNAs encoding P-57 from murine brain cDNA libraries in the expression vector lambda gt 11. Two of the overlapping clones contained an open reading frame encoding a polypeptide of 227 amino acid residues (predicted Mr, 23,635), a 163-nucleotide 5'-untranslated sequence, and a 403-nucleotide 3'-untranslated sequence. Hydrophobicity analysis of the predicted polypeptide indicated the lack of any considerable stretch of hydrophobic residues that may span the membrane. This is consistent with prior data suggesting that P-57 exists in a soluble, as well as a membrane-associated, form. The predicted amino acid composition of P-57 is rather unusual in that it is highly enriched in alanine, glutamic acid, and lysine residues, and relatively enriched with proline residues. This amino acid composition accounts for the very low helical content of the predicted polypeptide. A search of the GenBank and EMBL sequence data banks (GenBank Inc., release 44.0 (August, 1986); European Molecular Biology Library, release 8.0 (April, 1986] indicated that the P-57 nucleotide sequence shows no significant homology to any reported sequences. RNA blot analysis of brain, heart, liver, and testes RNA revealed that cDNAs detect P-57 transcripts of 1.5 kilobases in brain, but not in other tissues. Genome blot analysis was consistent with P-57 being encoded by a single or small number of genes. These data demonstrate that the accumulation of this novel calmodulin-binding polypeptide in neural tissue is controlled primarily at the level of RNA abundance.

Physicochemical and hydrodynamic characterization of P-57, a neurospecific calmodulin binding protein

P-57 is a neurospecific calmodulin binding protein that was discovered by virtue of its unusual interactions with calmodulin-Sepharose [Andreasen, T. J., Luetje, C. W., Heideman, W., & Storm, D. R. (1983) Biochemistry 22, 4615-4618; Cimler, B. M., Andreasen, T. J., Andreasen, K. I., & Storm, D. R. (1985) J. Biol. Chem. 260, 10784-10788]. In contrast to other calmodulin binding proteins, P-57 has higher affinity for calmodulin-Sepharose in the absence of calcium compared to that in the presence of calcium. In this study, we report the chemical and physical properties of P-57 purified from detergent-solubilized bovine brain membranes. The amino acid composition of P-57 is distinctive in that it contains a single phenylalanine residue with no other aromatic amino acids and a relatively high percentage of proline and alanine. In the presence of 0.05% Lubrol PX, its predicted secondary structure from circular dichroism spectroscopy is 1% alpha-helix, 21% beta-sheet, and 78% random coil. The hydrodynamic characteristics of the protein-detergent complex and the molecular weight of the protein were determined by gel filtration and sucrose density gradient sedimentation in the presence and absence of calmodulin. The P-57-detergent complex has an apparent Stokes radius (Rs) of 4.58 nm and a sedimentation coefficient (S20,w) of 1.44 S while the Stokes radius and S20,w for the P-57-calmodulin-detergent complex are 5.33 nm and 2.32 S, respectively. Perrin analysis of a 5-[[[(iodoacetyl)amino]ethyl]amino]-1-naphthalenesulfonic acid (AEDANS) derivative of P-57 confirmed the Stokes radius determined by gel filtration.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane association of the carbon monoxide oxidation system in Rhodopseudomonas gelatinosa

A comparison of the distribution of CO oxidation activity between soluble and particulate protein fractions obtained after disruption of CO-grown Rhodopseudomonas gelatinosa 1 by French pressure cell breakage and osmotic lysis of spheroplasts suggested that, in situ, the enzyme complex was associated with the cell membrane. An improved, strictly anaerobic method is given for spectrophotometric measurement of CO oxidation activity based on the carbon monoxide:methyl viologen oxidoreductase reaction.