Local Peroxynitrite Impairs Endothelial Transient Receptor Potential Vanilloid 4 Channels and Elevates Blood Pressure in Obesity

BACKGROUND

Impaired endothelium-dependent vasodilation is a hallmark of obesity-induced hypertension. The recognition that Ca2+ signaling in endothelial cells promotes vasodilation has led to the hypothesis that endothelial Ca2+ signaling is compromised during obesity, but the underlying abnormality is unknown. In this regard, transient receptor potential vanilloid 4 (TRPV4) ion channels are a major Ca2+ influx pathway in endothelial cells, and regulatory protein AKAP150 (A-kinase anchoring protein 150) enhances the activity of TRPV4 channels.

METHODS

We used endothelium-specific knockout mice and high-fat diet-fed mice to assess the role of endothelial AKAP150-TRPV4 signaling in blood pressure regulation under normal and obese conditions. We further determined the role of peroxynitrite, an oxidant molecule generated from the reaction between nitric oxide and superoxide radicals, in impairing endothelial AKAP150-TRPV4 signaling in obesity and assessed the effectiveness of peroxynitrite inhibition in rescuing endothelial AKAP150-TRPV4 signaling in obesity. The clinical relevance of our findings was evaluated in arteries from nonobese and obese individuals.

RESULTS

We show that Ca2+ influx through TRPV4 channels at myoendothelial projections to smooth muscle cells decreases resting blood pressure in nonobese mice, a response that is diminished in obese mice. Counterintuitively, release of the vasodilator molecule nitric oxide attenuated endothelial TRPV4 channel activity and vasodilation in obese animals. Increased activities of inducible nitric oxide synthase and NADPH oxidase 1 enzymes at myoendothelial projections in obese mice generated higher levels of nitric oxide and superoxide radicals, resulting in increased local peroxynitrite formation and subsequent oxidation of the regulatory protein AKAP150 at cysteine 36, to impair AKAP150-TRPV4 channel signaling at myoendothelial projections. Strategies that lowered peroxynitrite levels prevented cysteine 36 oxidation of AKAP150 and rescued endothelial AKAP150-TRPV4 signaling, vasodilation, and blood pressure in obesity. Peroxynitrite-dependent impairment of endothelial TRPV4 channel activity and vasodilation was also observed in the arteries from obese patients.

CONCLUSIONS

These data suggest that a spatially restricted impairment of endothelial TRPV4 channels contributes to obesity-induced hypertension and imply that inhibiting peroxynitrite might represent a strategy for normalizing endothelial TRPV4 channel activity, vasodilation, and blood pressure in obesity.

Interferon-alpha receptor 1 mRNA expression in peripheral blood mononuclear cells is associated with response to interferon-alpha therapy of patients with chronic hepatitis C

Interferon (IFN)-alpha receptor mRNA expression in liver of patients with chronic hepatitis C has been shown to be a response to IFN-alpha therapy. The objective of the present study was to determine whether the expression of mRNA for subunit 1 of the IFN-alpha receptor (IFNAR1) in peripheral blood mononuclear cells (PBMC) is associated with the response to IFN-alpha in patients with chronic hepatitis C. Thirty patients with positive anti-HCV and HCV-RNA, and abnormal levels of alanine aminotransferase in serum were selected and treated with IFN-alpha 2b for one year. Those with HBV or HIV infection, or using alcohol were not included. Thirteen discontinued the treatment and were not evaluated. The IFN-alpha response was monitored on the basis of alanine aminotransferase level and positivity for HCV-RNA in serum. IFNAR1-mRNA expression in PBMC was measured by reverse transcription-polymerase chain reaction before and during the first three months of therapy. The results are reported as IFNAR1-mRNA/beta-actin-mRNA ratio (mean +/- SD). Before treatment, responder patients had significantly higher IFNAR1-mRNA expression in PBMC (0.67 +/- 0.15; N = 5; P < 0.05) compared to non-responders (0.35 +/- 0.17; N = 12) and controls (0.30 +/- 0.16; N = 9). Moreover, IFNAR1-mRNA levels were significantly reduced after 3 months of treatment in responders, whereas there were no differences in IFNAR1 expression in non-responders during IFN-alpha therapy. Basal IFNAR1-mRNA expression was not correlated with the serum level of alanine and aspartate aminotransferases or the presence of cirrhosis. The present results suggest that IFNAR1-mRNA expression in PBMC is associated with IFN-alpha response to hepatitis C and may be useful for monitoring therapy in patients with chronic hepatitis C.

Peptide nucleic acid probe detection of mutations in Mycobacterium tuberculosis genes associated with drug resistance

The emergence of drug-resistant strains of Mycobacterium tuberculosis is a serious public health problem. Many of the specific gene mutations that cause drug resistance in M. tuberculosis are point mutations. We are developing a PCR-peptide nucleic acid (PNA)-based ELISA as a diagnostic method to recognize point mutations in genes associated with isoniazid and rifampin resistance in M. tuberculosis. Specific point mutation-containing sequences and wild-type sequences of cloned mycobacterial genes were PCR-amplified, denatured, and hybridized with PNA probes bound to microplate wells. Using 15-base PNA probes, we established the hybridization temperatures (50 degrees C-55 degrees C) and other experimental conditions suitable for detecting clinically relevant point mutations in the katG and rpoB genes. Hybridization of PCR-amplified sequences that contained these point mutations with complementary mutation-specific PNAs resulted in significant increases in ELISA response compared with hybridization using wild-type-specific PNAs. Conversely, PCR-amplified wild-type sequences hybridized much more efficiently with wild-type PNAs than with the mutation-specific PNAs. Using the M. tuberculosis cloned genes and PCR-PNA-ELISA format developed here, M. tuberculosis sequences containing point mutations associated with drug resistance can be identified in less than 24 h.

Mapping the binding site of colchicinoids on beta -tubulin. 2-Chloroacetyl-2-demethylthiocolchicine covalently reacts predominantly with cysteine 239 and secondarily with cysteine 354

2-Chloroacetyl-2-demethylthiocolchicine (2CTC) and 3-chloroacetyl-3-demethylthiocolchicine (3CTC) resemble colchicine in binding to tubulin and react covalently with beta-tubulin, forming adducts with cysteine residues 239 and 354. The adducts at Cys-239 are less stable than those at Cys-354 during formic acid digestion. Extrapolating to zero time, the Cys-239 to Cys-354 adduct ratio is 77:23 for 2CTC and 27:73 for 3CTC. Using energy minimization modeling to dock colchicinoids into the electron crystallographic model of beta-tubulin in protofilaments (Nogales, E. , Wolf, S. G., and Downing, K. H. (1998) Nature 391, 199-203), we found two potential binding sites. At one, entirely encompassed within beta-tubulin, the C2- and C3-oxygen atoms of 2CTC and 3CTC overlapped poorly with those of colchicine and thiocolchicine, but distances from the reactive carbon atoms of the analogs to the sulfur atoms of the cysteine residues were qualitatively consistent with reactivity. The other potential binding site was located at the alpha/beta interface. Here, the oxygen atoms of the analogs overlapped well with those of colchicine, but relative distances of the reactive carbons to the cysteine sulfur atoms did not correlate with the observed reactivity. A significant conformational change must occur in the colchicine binding site of tubulin in the transition from the unpolymerized to the polymerized state.

Expression and biological activity of two recombinant polypeptides related to subunit 1 of the interferon-alpha receptor

Abnormal production of interferon alpha (IFN-alpha) has been found in certain autoimmune diseases and can be also observed after prolonged therapy with IFN-alpha. IFN-alpha can contribute to the pathogenesis of allograft rejection in bone marrow transplants. Therefore, the development of IFN-alpha inhibitors as a soluble receptor protein may be valuable for the therapeutic control of these diseases. We have expressed two polypeptides encoding amino acids 93-260 (P1) and 261-410 (P2) of the extracellular domain of subunit 1 of the interferon-alpha receptor (IFNAR 1-EC) in E. coli. The activities of the recombinant polypeptides and of their respective antibodies were evaluated using antiproliferative and antiviral assays. Expression of P1 and P2 polypeptides was achieved by transformation of cloned plasmid pRSET A into E. coli BL21(DE3)pLysS and by IPTG induction. P1 and P2 were purified by serial sonication steps and by gel filtration chromatography with 8 M urea and refolded by dialysis. Under reducing SDS-PAGE conditions, the molecular weight of P1 and P2 was 22 and 17 kDa, respectively. Polyclonal anti-P1 and anti-P2 antibodies were produced in mice. P1 and P2 and their respective polyclonal antibodies were able to block the antiproliferative activity of 6.25 nM IFN-alphaB on Daudi cells, but did not block IFN-alphaB activity at higher concentrations (>6. 25 nM). On the other hand, the polypeptides and their respective antibodies did not inhibit the antiviral activity of IFN-alphaB on Hep 2/c cells challenged with encephalomyocarditis virus.

Detection of apolipoprotein B mRNA editing by peptide nucleic acid mediated PCR clamping

Apolipoprotein B (apoB) mRNA editing leads to a single base change in its mRNA and the production of apoB-48. Currently, the degree of apoB mRNA editing is analyzed by the RT-PCR primer extension method. While this method is quantitative, it is labor intensive, utilizes radioactivity for labeling and may not be sensitive enough to discriminate between low levels of editing and inherent assay background levels. Peptide nucleic acid (PNA) oligonucletides have been used in single point mutation detection through PCR clamping. In the present work, we developed a PCR based assay which can detect the single base change responsible for the apoB-48 production. We found that as low as 0.5% of the edited form can be clearly detected by PNA mediated PCR clamping. When combined with the primer extension assay, an approximately 180-fold enrichment of the edited percentage is observed, reflecting selected PCR amplification of templates containing the edited base.

Direct photoaffinity labeling of cysteine 211 or a nearby amino acid residue of beta-tubulin by guanosine 5'-diphosphate bound in the exchangeable site

Tubulin with [8-14C]GDP bound in the exchangeable site was exposed to ultraviolet light, and radiolabel was cross-linked to two peptide regions of the beta-subunit. Following enrichment for peptides cross-linked to guanosine by boronate chromatography, we confirmed that the cysteine 12 residue was the major site of cross-linking. However, significant radiolabel was also incorporated into a peptide containing amino acid residues 206 through 224. Although every amino acid in this peptide except cysteine 211 was identified by sequential Edman degradation, implying that this was the amino acid residue cross-linked to guanosine, radiolabel at C-8 was usually lost during peptide processing (probably during chromatography at pH 10). Consequently, the radiolabeled amino acid could not be unambiguously identified.

Mutant analysis of Prevotella sp. plaA-lacZ fusion protein expression in Escherichia coli: support for an essential role of the stem-loop

This study investigated the involvement of RNA folding in the synthesis of a fusion protein with beta-galactosidase activity. The coding gap region of the Prevotella loescheii adhesin gene plaA was fused in-frame with the Escherichia coli lacZ gene on plasmid pSK105. N-Terminal sequencing of the expressed plaA-lacZ protein indicated that it resulted from translational initiation at a fortuitous ribosomal-binding site within the plaA sequence at nt 570. Specific mutations were introduced in the stem-loop region that precedes the gap sequence. Analysis of stem-loop mutants, together with the introduction of compensatory mutations that restored activity, supports a requirement for stem-loop formation within the plaA sequence preceding the translational initiation site. A mutation reducing the predicted size of the loop, but preserving the stem structure, inactivated fusion protein synthesis. A suppressor mutation predicted to restore the size of the loop restored efficient fusion protein synthesis. In addition, the sequence preceding the translational start site of the plaA-lacZ fusion has several similarities to sequences that function as translational enhancers in prokaryotes. These include a stem-loop structure, an A-U rich region preceding the initiation codon, and a region of homology to 16S rRNA.

The translational hop junction and the 5' transcriptional start site for the Prevotella loescheii adhesin encoded by plaA

The Prevotella loescheii adhesin gene, plaA, contains a coding gap between a small open reading frame (ORF-1) and a large open reading frame (ORF-2). Translation of the plaA mRNA requires bypassing this 29-nt coding gap on the plaA transcript. We have determined the N-terminal peptide sequence of the SO34 adhesin beyond the gap sequence. This sequence shows that the peptide junction between ORF-1 and ORF-2 is continuous in the adhesin and supports the conclusion that synthesis of the SO34 adhesin occurs by a ribosomal hop mechanism. To elucidate upstream signals, we used the 5' RACE (rapid amplification of cDNA ends) technique to map the start point of the plaA mRNA. DNA sequencing of plasmids with the 5' RACE products placed the 5' end of plaA mRNA 270 nt upstream from the plaA start codon. A region corresponding to a Bacteroides fragilis promoter consensus sequence precedes this start site.

Direct photoaffinity labeling of cysteine-295 of alpha-tubulin by guanosine 5'-triphosphate bound in the nonexchangeable site

The alphabeta-tubulin heterodimer has two high affinity guanosine 5'-triphosphate binding sites, so that purified tubulin usually contains two molecules of bound guanosine nucleotide. Half this nucleotide is freely exchangeable with exogenous guanine nucleotide, and its binding site has been readily localized to the beta-subunit. The remaining nonexchangeable guanosine 5'-triphosphate can only be released from tubulin by denaturing the protein. We replaced the exchangeable site nucleotide of tubulin with 2'-deoxyguanosine 5'-diphosphate, exposed the resulting tubulin to ultraviolet light, degraded the protein, and isolated ribose-containing peptide derived from the nonexchangeable site. A large cyanogen bromide peptide was recovered, and its further degradation with endoproteinase Glu-C established that cysteine-295 of alpha-tubulin was the major reactive amino acid cross-linked to guanosine by ultraviolet irradiation.

Regulation of the receptor specificity and function of the chemokine RANTES (regulated on activation, normal T cell expressed and secreted) by dipeptidyl peptidase IV (CD26)-mediated cleavage

CD26 is a leukocyte activation marker that possesses dipeptidyl peptidase IV activity but whose natural substrates and immunological functions have not been clearly defined. Several chemo-kines, including RANTES (regulated on activation, normal T cell expressed and secreted), have now been shown to be substrates for recombinant soluble human CD26. The truncated RANTES(3-68) lacked the ability of native RANTES(1-68) to increase the cytosolic calcium concentration in human monocytes, but still induced this response in macrophages activated with macrophage colony-stimulating factor. Analysis of chemokine receptor messenger RNAs and patterns of desensitization of chemokine responses showed that the differential activity of the truncated molecule results from an altered receptor specificity. RANTES(3-68) showed a reduced activity, relative to that of RANTES(1-68), with cells expressing the recombinant CCR1 chemokine receptor, but retained the ability to stimulate CCR5 receptors and to inhibit the cytopathic effects of HIV-1. Our results indicate that CD26-mediated processing together with cell activation-induced changes in receptor expression provides an integrated mechanism for differential cell recruitment and for the regulation of target cell specificity of RANTES, and possibly other chemokines.

Evidence for cell-surface association between fusin and the CD4-gp120 complex in human cell lines

Accessory cell-surface molecules involved in the entry of human immunodeficiency virus-type 1 into cells have recently been identified and shown to belong to the family of chemokine receptors. Treatment of human cell lines with soluble monomeric gp120 at 37 degrees C induced an association between the surface CD4-gp120 complex and a 45-kilodalton protein, which can be down-modulated by the phorbol ester phorbol 12-myristate 13-acetate. The three proteins were coprecipitated from the cell membranes with antibodies to CD4 or to gp120. The 45-kilodalton protein comigrated with fusin on sodium dodecyl sulfate gels and reacted with rabbit antisera to fusin in protein immunoblots. No 45-kilodalton protein could be coprecipitated from similarly treated nonhuman cells. However, infection of 3T3.CD4.401 cells with vaccinia-fusin recombinant virus (vCBYF1), followed by gp120 treatment, resulted in coprecipitation of fusin and CD4.401 molecules from their membranes. Together these data provide evidence for physical association between fusin and the CD4-gp120 complex on cell membranes.

Human interferon-alpha receptor: identification of the region involved in binding to interferon-alpha B

Three polypeptides comprising amino acids 1-102, 93-260, and 261-410 of the extracellular domain of the human interferon-alpha receptor HuIFN-alpha R (Uzé, G., Lutfalla, G., and Gresser, I. Cell 1990; 60:225-234) have been expressed in Escherichia coli. The polypeptides were sequestered within bacterial inclusion bodies. Inclusion body material was solubilized by 8 M urea, and the polypeptides were purified by gel filtration or histidine tag-based affinity chromatography. Overall recovery of each purified and refolded polypeptide was approximately 0.5-0.8 mg/liter of cell culture. The polypeptides migrated as homogeneous monomers of 12 kDa, 22 kDa, and 17 kDa, respectively on reduced sodium dodecylsulfate polyacrylamide gel electrophoresis. The polypeptide fragments corresponding to amino acids 1-102, and 93-260 of the extracellular domain of HuIFN-alpha R lacked the ability to bind to IFN-alpha B and to inhibit its biologic activities. The polypeptide fragment corresponding to amino acids 261-410 of the receptor molecule inhibited the antiproliferative activity of IFN-alpha B and competed with the Daudi cell surface receptor for binding to this IFN-alpha species.

Isolation of a biologically active soluble human interferon-alpha receptor-GST fusion protein expressed in Escherichia coli

The cDNA encoding the extracellular domain of the human interferon-alpha (IFN-alpha) receptor (Uzé, G., Lutfalla, G., and Gresser, I. Cell 1990;60:225-234) lacking the signal peptide has been expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The fusion protein represented 12% of total bacterial proteins and was found exclusively within cytoplasmic inclusion bodies. Inclusion body material was completely solubilized by 8 M urea; 20% solubilization was achieved by cell lysis in the presence of 0.45% cholamidopropyl dimethylammoniol-propane sulfonate and 1% Triton X-100. The soluble fusion protein was purified by gel filtration and affinity chromatography. Overall recovery of affinity purified fusion protein was approximately 100-200 micrograms/liter of cell culture. The affinity purified and refolded fusion protein exhibited the expected amino terminal sequence and M(r) of 68,000 on reduced sodium dodecylsulfate gel electrophoresis. The protein reacted with antibodies specific for the cloned IFN-alpha receptor and inhibited the antiviral and antiproliferative activities of recombinant IFN-alpha B. We have demonstrated that the fusion protein binds to IFN-alpha B and competes with the cell surface receptor for binding to this IFN-alpha species.

Identification of cysteine 354 of beta-tubulin as part of the binding site for the A ring of colchicine

The colchicine analog 3-chloroacetyl-3-demthylthio-colchicine (3CTC) is a competitive inhibitor of colchicine binding to tubulin, binds to tubulin at 37 degrees C, but not at 0 degree C, and covalently reacts with beta-tubulin at 37 degree C, but not at 0 degree C, in a reaction inhibited by colchicine site drugs. The approximate intramolecular distance between the oxygen at position C-3 in 3CTC and the chlorine atom of the 3-chloroacetyl group is 3 A. using decylagarose chromatography, we purified beta-tubulin that had reacted with 3-(chloromethyl-[14C] Carbonyl)-3- demethylthiocolchicine ([14C]3CTC). This beta-tubulin that had reacted with 3-(chloromethyl-[14C]carbonyl)- 3-demethythiocolchicine ([14C]3CTC). This beta-tubulin was digested with formic acid, cyanogen bromide, endoproteinase Glu-C, or endoproteinase Lys-C, and the radio-labeled peptide(s) were isolated. The sequences of these peptides indicated that as much as 90% of the covalent reaction between the [14C]3CTC and beta-tubulin occurred at cysteine 354. This finding indicates that the C-3 oxygen atom of colchicinoids is within 3 A of the sulfur atom of the Cys-354 residue, suggests that the colchicine A ring lies between Cys-354 and Cys-239, based on the known 9 A distance between these residues, and may indicate that the tropolone C ring lies between the peptide region containing Cys-239 and the amino-terminal beta-tubulin sequence, based on the labeling pattern observed following direct photoactivation of tubulin-bound colchicine.

Purification from Fusobacterium mortiferum ATCC 25557 of a 6-phosphoryl-O-alpha-D-glucopyranosyl:6-phosphoglucohydrolase that hydrolyzes maltose 6-phosphate and related phospho-alpha-D-glucosides

6-Phosphoryl-O-alpha-D-glucopyranosyl:6-phosphoglucohydrolase (6-phospho-alpha-glucosidase) has been purified from Fusobacterium mortiferum ATCC 25557. p-Nitrophenyl-alpha-D-glucopyranoside 6-phosphate (pNP alpha Glc6P) served as the chromogenic substrate for detection and assay of enzyme activity. The O2-sensitive, metal-dependent phospho-alpha-glucosidase was stabilized during purification by inclusion of dithiothreitol and Mn2+ ion in chromatography buffers. Various 6-phosphoryl-O-alpha-linked glucosides, including maltose 6-phosphate, pNP alpha Glc6P, trehalose 6-phosphate, and sucrose 6-phosphate, were hydrolyzed by the enzyme to yield D-glucose 6-phosphate and aglycone moieties in a 1:1 molar ratio. 6-Phospho-alpha-glucosidase (M(r) of approximately 49,000; pI of approximately 4.9) is activated by Fe2+, Mn2+, Co2+, and Ni2+, and the maximum rate of pNP alpha Glc6P hydrolysis occurs at 40 degrees C within the pH range 7.0 to 7.5. The sequence of the first 32 amino acids of 6-phospho-alpha-glucosidase exhibits 67% identity (90% similarity) to that deduced for the N terminus of a putative phospho-beta-glucosidase (designated ORF f212) encoded by glvG in Escherichia coli. Western blots involving highly specific polyclonal antibody against 6-phospho-alpha-glucosidase and spectrophotometric analyses with pNP alpha Glc6P revealed only low levels of the enzyme in glucose-, mannose-, or fructose-grown cells of F. mortiferum. Synthesis of 6-phospho-alpha-glucosidase increased dramatically during growth of the organism on alpha-glucosides, such as maltose, alpha-methylglucoside, trehalose, turanose, and palatinose.

The Lactococcus lactis triosephosphate isomerase gene, tpi, is monocistronic

Triosephosphate isomerase (EC 5.3.1.1) from Lactococcus lactis was purified to electrophoretic homogeneity. Approximately 3 mg purified enzyme (specific activity 3300 U mg-1) was obtained from 70 g (wet wt) cells. In solution, triosephosphate isomerase (pI 4.0-4.4) was observed to exist as a homodimer (M(r) 57,000) of noncovalently linked subunits. The sequence of the first 37 amino acid residues from the NH2-terminus were determined by step-wise Edman degradation. This sequence, and that of a region conserved in all known bacterial triosephosphate isomerases, was used to design oligonucleotide primers for the synthesis of a lactococcal tpi probe by PCR. The probe was used to isolate a molecular clone of tpi from a lambda GEM11 library of L. lactis LM0230 DNA. The nucleotide sequence of tpi predicted a protein of 252 amino acids with the same NH2-terminal sequence as that determined for the purified enzyme and a subunit M(r) of 26,802 after removal of the NH2-terminal methionine. Escherichia coli cells harbouring a plasmid containing tpi had 15-fold higher triosephosphate isomerase activity than isogenic plasmid-free cells, confirming the identity of the cloned gene. Northern analysis of L. lactis LM0230 RNA showed that a 900 base transcript hybridized with tpi. The 5' end of the transcript was determined by primer extension analysis to be a G located 65 bp upstream from the tpi start codon. These transcript analyses indicated that in L. lactis, tpi is expressed on a monocistronic transcript. Nucleotide sequencing indicated that the DNA adjacent to tpi did not encode another Embden-Meyerhoff-Parnas pathway enzyme. The location of tpi on the L. lactis DL11 chromosome map was determined to be between map coordinates 1.818 and 1.978.

Crystallization and preliminary X-ray diffraction studies of dogfish C-reactive protein

Crystals of dogfish (Mustelus canis) C-reactive protein were obtained through vapor phase equilibration using the sitting drop rod technique with ammonium sulfate as the precipitating agent. The space group was determined to be P1 (triclinic lattice) with unit cell dimensions of a = 82.91, b = 92.25 and c = 103.40 A; alpha = 83.36 degrees, beta = 89.76 degrees, and gamma = 81.30 degrees. These crystals diffract to about 2.6 A resolution and contain two hexamers in the asymmetric unit.

Isolation, cDNA cloning, and characterization of an 18-kDa hemagglutinin and amebocyte aggregation factor from Limulus polyphemus

An 18-kDa hemagglutinin which possesses the property of inducing both aggregation of amebocytes and agglutination of erythrocytes has been isolated from Limulus polyphemus amebocytes and purified by ion exchange chromatography. This nonglycosylated, single chain polypeptide with an M(r) of 18,506 and isoelectric point of 8.3 is stored exclusively in the large secretory granules of amebocytes. Based on the partial N-terminal amino acid sequence of 63 residues, DNA probes have been synthesized for screening a pBR322 cDNA library constructed from Limulus amebocytes. The cDNA coding for this protein reveals the presence of a 19-residue signal peptide preceding the 153-residue open reading frame. Northern blot analysis indicates the presence of a single mRNA species. The primary structure derived from the corresponding cDNA sequence reveals an internal homology consisting of two consensus sequences, Val-Asn-Asp/Ser-Trp-Asp and Glu-Asp-Arg-Arg-Trp. The formation of 5 disulfide bonds between 10 half-cysteines divides the molecule into three looped domains each containing the Glu-Asp-Arg-Arg-Trp repeating unit. One of the novel features of this protein is that it shares 37% identity with a 22-kDa mammalian extracellular matrix protein isolated from fetal bovine skin (Neame, P.J., Choi, H.U., and Rosenberg, L.C. (1989) J. Biol. Chem. 264, 5474-5479). The two proteins exhibit a similar pattern of looped domains, each domain containing a homologous consensus sequence (i.e. Glu-Asp-Arg-Arg-Trp). The overall structure of both proteins seems to be highly related, with the exception of an N-terminal tyrosine-rich region present only in the mammalian extracellular matrix protein. The functional properties of the two proteins are similar in that the Limulus 18-kDa protein agglutinates horse erythrocytes and aggregates Limulus amebocytes, and the mammalian 22-kDa protein is an effective adhesion promoter for dermal fibroblasts. On the basis of these unique properties, the newly characterized hemagglutinin has been termed Limulus 18K agglutination-aggregation factor (18K-LAF).

Purification and characterization of multiple components of human lymphoblastoid interferon-alpha

Twenty-two components of human interferon-alpha (IFN-alpha) derived from Sendai virus-induced Namalwa cells were purified by sequential immunoadsorbent affinity chromatography using four monoclonal antibody affinity columns followed by ultrafiltration and reversed-phase high-performance liquid chromatography. The specific activity ranged from 0.2 to 2.6 x 10(8) IU/mg protein on Madin-Darby bovine kidney cells, 0.3 to 4.6 x 10(8) IU/mg protein on human WISH cells, and 10(4) to 7 x 10(5) units/mg protein on mouse L929 cells. The apparent molecular weights of the components ranged from 17,500 to 23,300 using nonreducing sodium dodecyl polyacrylamide-gel electrophoresis and 17,500 to 27,600 using reducing sodium dodecyl polyacrylamide-gel electrophoresis. The amino-terminal amino acid sequences were similar among the components as well as to those reported for the cloned human IFN-alpha genes (Pestka, S. (1986) Methods Enzymol. 119, 3-14). However, four components, f, i, l, and m, have amino-terminal amino acid sequences which appear to be unique when compared to those predicted from the cDNA clones. One component, pre-a, has a potential N-linked glycosylation site on the Asn of residues 2 through 4, Asn-Leu-Ser.

Sucrose fermentation by Fusobacterium mortiferum ATCC 25557: transport, catabolism, and products

Studies of sucrose utilization by Fusobacterium mortiferum ATCC 25557 have provided the first definitive evidence for phosphoenolpyruvate-dependent sugar:phosphotransferase activity in the family Bacteroidaceae. The phosphoenolpyruvate-dependent sucrose:phosphotransferase system and the two enzymes required for the dissimilation of sucrose 6-phosphate are induced specifically by growth of F. mortiferum on the disaccharide. Monomeric sucrose 6-phosphate hydrolase (M(r), 52,000) and a dimeric ATP-dependent fructokinase (subunit M(r), 32,000) have been purified to electrophoretic homogeneity. The physicochemical and catalytic properties of these enzymes have been examined, and the N-terminal amino acid sequences for both proteins are reported. The characteristics of sucrose 6-phosphate hydrolase and fructokinase from F. mortiferum are compared with the same enzymes from both gram-positive and gram-negative species. Butyric, acetic, and D-lactic acids are the end products of sucrose fermentation by F. mortiferum. A pathway is proposed for the translocation, phosphorylation, and metabolism of sucrose by this anaerobic pathogen.

Transposon-encoded sucrose metabolism in Lactococcus lactis. Purification of sucrose-6-phosphate hydrolase and genetic linkage to N5-(L-1-carboxyethyl)-L-ornithine synthase in strain K1

Sucrose-6-phosphate hydrolase from Lactococcus lactis subsp. lactis K1-23 (formerly Streptococcus lactis K1-23) has been purified 600-fold to electrophoretic homogeneity. Purification of the enzyme was achieved by DEAE-Sephacel, phosphocellulose P-11, and gel exclusion (Ultrogel AcA 54) chromatography. The purified enzyme (specific activity 31 units/mg) catalyzed the hydrolysis of both 6-O-phosphoryl-alpha-D-glucopyranosyl-1,2-beta-D-fructofuranoside (sucrose 6-phosphate) and sucrose (Km = 0.1 and 100 mM, respectively). Ultracentrifugal analysis of sucrose-6-phosphate hydrolase indicated an Mr = 52,200. The purified enzyme migrated as a single protein during sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr = 52,000). However, four distinct polypeptides were detected by analytical electrofocusing, and all four species hydrolyzed sucrose and sucrose 6-phosphate. The amino acid composition of sucrose-6-phosphate hydrolase, and the sequence of the first 12 amino acids from the NH2 terminus, have been determined. Hybridization studies with oligonucleotide probes show that the genes for sucrose-6-phosphate hydrolase (scrB), Enzyme IIScr of the phosphoenolypyruvate-dependent sucrose:phosphotransferase system (scrA), and N5-(carboxyethyl)ornithine synthase (ceo) are encoded by the same approximately 20-kilobase EcoRI fragment. This fragment is part of a large transposon Tn5306 that also encodes the nisin precursor gene, spaN, and IS904. In L. lactis ATCC 11454, spaN, IS904, scrA, and scrB (but not ceo) are encoded on a related transposon, Tn5307.

Cloning and sequencing of the structural gene for the porin protein of Bordetella pertussis

Bordetella pertussis produces a porin protein which is a prominent outer membrane component found in both virulent and avirulent strains. N-terminal amino acid analysis of purified B. pertussis porin was performed and this amino acid sequence was used to design an oligonucleotide that was then utilized to screen a lambda gt11 library containing randomly sheared fragments of DNA from B. pertussis strain 347. One clone, lambda BpPor, was identified and subcloned into pUC18. A portion of the DNA insert in this subclone, pBpPor1, was sequenced and shown to contain the N-terminal region of the structural porin gene. This truncated gene sequence was used to design an additional oligonucleotide that was used to identify a clone, pBpPor2, which overlapped with pBpPor1 and contained a termination codon. The structural gene deduced from this sequence would encode a 365-amino-acid polypeptide with a predicted mass of 39,103 daltons. The predicted product also contains a signal sequence of 20 residues that is similar to that found in other porin genes. The predicted B. pertussis porin protein sequence contains regions that are homologous to regions found in porins expressed by Neisseria species and Escherichia coli, including the presence of phenylalanine as the carboxy-terminal amino acid. DNA hybridization studies indicated that both virulent and avirulent strains of B. pertussis contain only one copy of this gene and that Bordetella bronchiseptica and Bordetella parapertussis contain a similar gene.

Identification of the cysteine residue of beta-tubulin alkylated by the antimitotic agent 2,4-dichlorobenzyl thiocyanate, facilitated by separation of the protein subunits of tubulin by hydrophobic column chromatography

The mechanism of action of the antimitotic drug 2,4-dichlorobenzyl thiocyanate (DCBT) has been examined in detail. Shown in previous studies to inhibit tubulin polymerization [Abraham, I., Dion, R. L., Duanmu, C., Gottesman, M. M., & Hamel, E. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 6839-6843] and to form a covalent bond preferentially with beta-tubulin [Bai, R., Duanmu, C., & Hamel, E. (1989) Biochim. Biophys. Acta 994, 12-20], DCBT has now been documented to interact at low concentrations with a high degree of specificity at cysteine residue 239 of beta-tubulin. These low DCBT concentrations also result in the partial inhibition of tubulin polymerization. Such findings strongly indicate that cysteine-239 of beta-tubulin is essential for microtubule assembly. Although alpha-tubulin is alkylated almost as well as beta-tubulin when the drug:tubulin ratio = 5:1 (Bai et al., 1989), beta-tubulin is alkylated about 25 times as extensively as alpha-tubulin, almost exclusively at Cys-239, when the drug:tubulin ratio = 1:5. In addition, we find that low concentrations of DCBT do not affect the binding of colchicine to tubulin but that colchicine and related compounds do reduce the alkylation of tubulin by DCBT. This suggests that Cys-239 of beta-tubulin is not involved in the binding of colchicine to tubulin but that this amino acid residue is at least partially masked by the drug when it is bound to the protein. We also describe a column chromatography procedure (hydrophobic chromatography on decylagarose) useful for the preparative resolution of unalkylated, although denatured, alpha- and beta-tubulin.

Reproducible high yield sequencing of proteins electrophoretically separated and transferred to an inert support

A method allowing initial sequencing yields of 60-85% to be consistently obtained from samples prepared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretic transfer is described in detail. Conducting electrophoresis at a pH near neutrality is the single most important of the modifications made to earlier procedures, but pre-electrophoresis in the presence of glutathione or sodium thioglycolate and use of Immobilon polyvinylidene difluoride membranes all contribute to the success of the technique. When tryptophan was the NH2 terminus of a protein, the phenylthiohydantoin (PTH)-derivative recovered appeared to be an irreversible oxidation product if pre-electrophoresis was not performed. Following pre-electrophoresis, the PTH-derivative recovered co-migrated with that of unmodified tryptophan, and the recovery was higher. Recovery of methionine as its PTH-derivative was not affected by pre-electrophoresis suggesting that thioglycolate in the electrophoresis buffer during sample separation prevented or reversed oxidation of methionine sulfur but did not protect tryptophan.

Isolation and characterization of Limulus C-reactive protein genes

Three homologous genes coding for Limulus C-reactive protein (CRP) have been isolated and characterized from a lambda phage EMBL-3 library containing genomic DNA sequences from Limulus amebocytes. The genes have a typical promoter region with a CAAT (nucleotides 50-53) and a TATAA (nucleotides 77-81) box located, respectively, 178 and 149 base pairs 5' upstream from the initiation codon ATG. The polyadenylation site AATAAA is situated within 300 base pairs downstream from the stop codon TAG. Nucleotide sequence analysis reveals a 24-residue signal peptide preceding a coding region of 218 amino acids. Significant differences were found between the genes coding for human and Limulus CRPs. In the human CRP gene there is an intron separating the signal peptide and the coding region. In Limulus this intervening sequence is missing. The Drosophila heat shock consensus sequence CTnGAAnnTTnAG (Simon, J. A., Sutton, C. A., Lobell, R. B., Glaser, R. L., and Lis, J. T. (1985) Cell 40, 805-817), found in the genes of human (Woo, P., Korenberg, J. R., and Whitehead, A. S. (1985) J. Biol. Chem. 260, 13384-13388) and rabbit (Syin, C., Gotschlich, E. C., and Liu, T.-Y. (1986) J. Biol. Chem. 261, 5473-5479) CRP at the 5' end, is not found in the Limulus CRP genes. Whereas a single CRP gene was found in the human, multiple genes were found for the Limulus CRPs. All CRPs exhibit calcium-dependent phosphorylcholine ligand binding properties. The coding regions of the Limulus and human CRP genes share approximately 25% identity and two stretches of highly conserved regions, one of which falls in the region proposed as the phosphorylcholine binding site, while the other site is very similar to the consensus sequence required for calcium binding in calmodulin and related proteins. The nucleotide sequence analysis provides convincing evidence to support the evolutionary relatedness of the human and Limulus CRPs.

The amino acid sequence of Limulus C-reactive protein. Evidence of polymorphism

The amino acid sequence, the positions of the disulfide bonds, and the site of glycosylation for the three subunits of Limulus C-reactive proteins (CRPs) 1.1, 1.4, and 3.3 have been established. The three subunits were shown to exist approximately in equimolar amount and are tightly associated. The hexagonal structure of Limulus CRP, as revealed by electron microscopic studies of Fernandez-Moran et al. (Fernandez-Moran, H., Marchalonis, J., and Edelman, G. M. (1968) J. Mol. Biol. 32, 467-469) might consist of two each of the subunits. The three subunits share an identical amino-terminal sequence of 44 residues and a carboxyl-terminal sequence from residues 206 to 218. Microheterogeneity exists to the extent of 10 to 11% for the entire protein. The positions of 6 half-cystines that form the three disulfide bonds and the site of glycosylation are constant in all subunits. Sequence analyses of peptides derived from enzymatic and chemical cleavages of affinity purified Limulus CRP indicate that subunits other than the three mentioned above exist in the hemolymph. Limulus CRP is therefore polymorphic. Topological analyses of Limulus CRPs, human CRP, rabbit CRP, human amyloid P-component, and Syrian hamster female protein indicate that the seven proteins may originate from the same ancestral gene. Using the topological data generated from the amino acid sequences of the proteins, we calculate that human and Limulus CRPs diverged about 500 million years ago. This figure is in general agreement with the evolutionary distance postulated by anthropological estimation of 400-500 million years.

Isolation and characterization of monkey interphotoreceptor retinoid-binding protein, a unique extracellular matrix component of the retina

The interphotoreceptor retinoid-binding protein (IRBP) has been isolated from monkey interphotoreceptor matrix (IPM). Following gentle washing of the IPM from the retinal surface, the protein was purified to homogeneity by concanavalin A-Sepharose affinity chromatography, ion-exchange high-performance liquid chromatography (HPLC), and size-exclusion HPLC. Bovine IRBP was purified similarly and compared with the monkey protein. Sedimentation equilibrium analysis yielded a molecular weight of 106 000 +/- 2900 for the native monkey protein. Sedimentation velocity analysis gave a sedimentation coefficient of 5.4 +/- 0.3 S and a frictional ratio of 1.59, indicating an asymmetrical molecular shape. IRBP contains neutral sugar, including fucose, and sialic acid; the glycoprotein nature of the proteins probably accounts for the microheterogeneity observed in the electrofocusing pattern of both bovine and monkey IRBP. Both IRBPs have isoelectric points between 6.0 and 7.0. The fluorescence emission lambda max of the bound ligand was 470 nm with excitation at 340 nm, while the excitation lambda max was 333 nm with emission at 470 nm, for monkey IRBP incubated with exogenous all-trans-retinol. The amino acid compositions of the monkey and bovine proteins are similar; nonpolar amino acids account for over 50% of the residues, which may explain the apparent hydrophobic nature of the isolated proteins. The amino-terminal analyses indicated considerable homology between the monkey and bovine IRBPs in this region and verified the purity of the isolated proteins. IRBP thus appears to be a unique, conserved glycoprotein of the retinal extracellular matrix that could serve as a retinoid-transport vehicle.

Protein composition of plasmin preparation "homolysin"

A commercial preparation of human plasmin (Homolysin), capable of catalyzing the transformation of human growth hormone (hGH) into biologically activated species, was analyzed by electrophoresis and electrofocusing on polyacrylamide gel. Each major component of the preparation was characterized with regard to molecular size (retardation coefficient, KR), molecular net charge (y-intercept on the Ferguson plot, Y0), apparent isoelectric point (PI') and enzyme activity. The multiple components of Homolysin revealed by staining corresponded to various aggregation states of plasmin and exhibited full serine protease activity. Polyacrylamide gel electrophoresis of Homolysin in the presence of sodium dodecylsulfate (SDS) yielded 2 subunits which corresponded in molecular weight to the known plasmin subunits.

Isolation of human growth hormone isohormones D and E in milligram amounts (II), using isoelectric focusing on polyacrylamide gel

Human growth hormone (hGH) isohormones D and E were prepared from a partial enzymatic hydrolyzate catalyzed by plasmin, using isoelectric focusing on polyacrylamide gel to fractionate the digest. Separation between the two isohormones species was optimized by employing a maximally flattened pH gradient between pH's 4.3 and 5.6. Gel slices containing isohormones D and E were extracted and concentrated by Steady-State Stacking on polyacrylamide gel. The extract was purified by gel filtration and lyophilized. Overall yields of lyophilized isohormones D and E were 10.9 mg and represented a recovery of 51% relative to the densitometrically estimated isohormone concentrations in the hGH digest. Purity of the products, based on Lowry analysis, U.V. absorbance and radioimmunoassay (RIA) was 60-70%. The isolated isohormone species were active in the rat tibia-line assay and in the specific RIA for hGH.

Isolation of human growth hormone isohormones D and E in milligram amounts (I), using isotachophoresis on polyacrylamide gel

Human growth hormone (hGH) isohormones D and E were isolated from a plasmin digest of 150 mg hGH. Isotachophoresis on a cylindrical polyacrylamide gel of 18 mm diameter served to separate the various isohormone species. The "extended stack" was sliced, and slices containing hGH-D and -E were extracted by Steady-State Stacking on 1% agarose gel and collected in a 1 ml volume. The extract was purified on gel chromatography and lyophilized. The overall yield was approximately 19 mg of hGH (D + E) and 16 mg of hGH-(D, minor E). This represents a 62% recovery of the amount of hGH-D and -E in the digest estimated densitometrically. The purity of the product, based on Lowry analysis, specific RIA or UV-absorbance, was 91%. The isolated hGH-(D+E) exhibited an enhanced bioactivity in the rat tibia line assay.

A three-step method for isolating a few to several hundred milligrams of protein

An operationally simple general protein isolation method was devised from three previously available separation tools, and was tested by application to two demanding fractionation problems and for yield. One test system was the isolation by gel electrofocusing of two model proteins with pI values of 4.6 and 4.8, bovine serum albumin and ovalbumin, with a load of 220 mg each. The other test was the isolation of 10 mg of human growth hormone isohormone B from a mixture of closely migrating other isohormones. The three-step procedure comprises of: (1) separation into zones of homogeneous protein by gel electrofocusing; (2) excision of the zones of homogeneous protein from the gel followed by concentration of the protein to a small volume of solution by means of Steady-State Stacking; (3) purification from polyacrylamide-like contaminants and non-volatile buffers by gel filtration followed by lyophilization. The average overall recovery was 70--80%.