A deacylase in Rhizobium leguminosarum membranes that cleaves the 3-O-linked beta-hydroxymyristoyl moiety of lipid A precursors.
(9/1703)Lipid A from the nitrogen-fixing bacterium Rhizobium leguminosarum displays many structural differences compared with lipid A of Escherichia coli. R. leguminosarum lipid A lacks the usual 1- and 4'-phosphate groups but is derivatized with a galacturonic acid substituent at position 4'. R. leguminosarum lipid A often contains an aminogluconic acid moiety in place of the proximal glucosamine 1-phosphate unit. Striking differences also exist in the secondary acyl chains attached to E. coli versus R. leguminosarum lipid A, specifically the presence of 27-hydroxyoctacosanoate and the absence of laurate and myristate in R. leguminosarum. Recently, we have found that lipid A isolated by pH 4.5 hydrolysis of R. leguminosarum cells is more heterogeneous than previously reported (Que, N. L. S., Basu, S. S., White, K. A., and Raetz, C. R. H. (1998) FASEB J. 12, A1284 (abstr.)). Lipid A species lacking the 3-O-linked beta-hydroxymyristoyl residue on the proximal unit contribute to this heterogeneity. We now describe a membrane-bound deacylase from R. leguminosarum that removes a single ester-linked beta-hydroxymyristoyl moiety from some lipid A precursors, including lipid X, lipid IVA, and (3-deoxy-D-manno-octulosonic acid)2-lipid IVA. The enzyme does not cleave E. coli lipid A or lipid A precursors containing an acyloxyacyl moiety on the distal glucosamine unit. The enzyme is not present in extracts of E. coli or Rhizobium meliloti, but it is readily demonstrable in membranes of Pseudomonas aeruginosa, which also contains a significant proportion of 3-O-deacylated lipid A species. Optimal reaction rates are seen between pH 5.5 and 6.5. The enzyme requires a nonionic detergent and divalent metal ions for activity. It cleaves the monosaccharide lipid X at about 5% the rate of lipid IVA and (3-deoxy-D-manno-octulosonic acid)2-lipid IVA. 1H NMR spectroscopy of the deacylase reaction product, generated with lipid IVA as the substrate, confirms unequivocally that the enzyme cleaves only the ester-linked beta-hydroxymyristoyl residue at the 3-position of the glucosamine disaccharide. (+info)
Comparison of activation of CPT-11 by rabbit and human carboxylesterases for use in enzyme/prodrug therapy.
(10/1703)Several recent studies have examined the possibility of producing tumor-specific cytotoxicity with various enzyme/ prodrug combinations. The enzymes are targeted to tumor cells either with antibodies (ADEPT, antibody directed enzyme prodrug therapy) or with viruses (VDEPT). The goal of the present study was to identify an appropriate enzyme for use in activating the prodrug 7-ethyl-10-[4-(1-piper-idino)-1-piperidino]carbonyloxycamptothe cin (CPT-11). In this study, we compared the efficiency of CPT-11 metabolism by rabbit and human carboxylesterases in in vitro and in situ assays. Although the rabbit and human enzymes are very similar (81% identical; 86% homologous) and the active site amino acids are 100% identical, the rabbit enzyme was 100-1000-fold more efficient at converting CPT-11 to SN-38 in vitro and was 12-55-fold more efficient in sensitizing transfected cells to CPT-11. In vivo, Rh30 rhabdomyosarcoma cells expressing the rabbit carboxylesterase and grown as xenografts in immune-deprived mice were also more sensitive to CPT-11 than were control xenografts or xenografts expressing the human enzyme. Each of the three types of xenografts regressed when the mice were treated with CPT-11 given i.v. at 2.5 mg of CPT-11/kg/daily for 5 days/week for 2 weeks [(dx5)2] (one cycle of therapy), repeated every 21 days for a total of three cycles. However, following cessation of treatment, recurrent tumors were detected in seven of seven mice bearing control Rh30 xenografts and in two of seven mice bearing Rh30 xenografts that expressed the human enzyme. No tumors recurred in mice bearing xenografts that expressed the rabbit carboxylesterase. We conclude that rabbit carboxylesterase/CPT-11 may be a useful enzyme/prodrug combination. (+info)
Establishment of an activated macrophage cell line, A-THP-1, and its properties.
(11/1703)A new macrophage cell line with activated character and unique morphology was isolated by selecting adherent cells from the human monocytic cell line THP-1. The original THP-1 cells had been cultured for more than 9 years using 25 cm2 flasks, when cells with a different morphology appeared, adhering to the bottoms of the culture flasks. These were selected by discarding floating nonadherent cells at every subculture. Enrichment of adherent THP-1 cells with long processes proceeded during the cultivation. These adherent THP-1 showed remarkable phenotypic changes, not only morphologically, but also functionally. Namely, increased phagocytic activity, HLA-DR expression and MLR stimulator activity were remarkable. This adherent cell line was designated as activated-THP-1 (A-THP-1), since it demonstrated characteristics of activated macrophages continuously without exogenous stimulation. A cloned A-THP-1 cell line (A-THP-1 C1) also showed the same features and contained about 10% multinucleated giant cells probably caused by cell fusion. This A-THP-1 cell line, the first activated macrophage cell line to be established, provides a good model for understanding of activation mechanisms of macrophages and multinucleation. In this paper, morphological, immunological, and biological characters of this cell line are described. (+info)
Targeting proteins to the lumen of endoplasmic reticulum using N-terminal domains of 11beta-hydroxysteroid dehydrogenase and the 50-kDa esterase.
(12/1703)Previous studies identified two intrinsic endoplasmic reticulum (ER) proteins, 11beta-hydroxysteroid dehydrogenase, isozyme 1 (11beta-HSD) and the 50-kDa esterase (E3), sharing some amino acid sequence motifs in their N-terminal transmembrane (TM) domains. Both are type II membrane proteins with the C terminus projecting into the lumen of the ER. This finding implied that the N-terminal TM domains of 11beta-HSD and E3 may constitute a lumenal targeting signal (LTS). To investigate this hypothesis we created chimeric fusions using the putative targeting sequences and the reporter gene, Aequorea victoria green fluorescent protein. Transfected COS cells expressing LTS-green fluorescent protein chimeras were examined by fluorescent microscopy and electron microscopic immunogold labeling. The orientation of expressed chimeras was established by immunocytofluorescent staining of selectively permeabilized COS cells. In addition, protease protection assays of membranes in the presence and absence of detergents was used to confirm lumenal or the cytosolic orientation of the constructed chimeras. To investigate the general applicability of the proposed LTS, we fused the N terminus of E3 to the N terminus of the NADH-cytochrome b5 reductase lacking the myristoyl group and N-terminal 30-residue membrane anchor. The orientation of the cytochrome b5 reductase was reversed, from cytosolic to lumenal projection of the active domain. These observations establish that an amino acid sequence consisting of short basic or neutral residues at the N terminus, followed by a specific array of hydrophobic residues terminating with acidic residues, is sufficient for lumenal targeting of single-pass proteins that are structurally and functionally unrelated. (+info)
A protein phosphatase methylesterase (PME-1) is one of several novel proteins stably associating with two inactive mutants of protein phosphatase 2A.
(13/1703)Carboxymethylation of proteins is a highly conserved means of regulation in eukaryotic cells. The protein phosphatase 2A (PP2A) catalytic (C) subunit is reversibly methylated at its carboxyl terminus by specific methyltransferase and methylesterase enzymes which have been purified, but not cloned. Carboxymethylation affects PP2A activity and varies during the cell cycle. Here, we report that substitution of glutamine for either of two putative active site histidines in the PP2A C subunit results in inactivation of PP2A and formation of stable complexes between PP2A and several cellular proteins. One of these cellular proteins, herein named protein phosphatase methylesterase-1 (PME-1), was purified and microsequenced, and its cDNA was cloned. PME-1 is conserved from yeast to human and contains a motif found in lipases having a catalytic triad-activated serine as their active site nucleophile. Bacterially expressed PME-1 demethylated PP2A C subunit in vitro, and okadaic acid, a known inhibitor of the PP2A methylesterase, inhibited this reaction. To our knowledge, PME-1 represents the first mammalian protein methylesterase to be cloned. Several lines of evidence indicate that, although there appears to be a role for C subunit carboxyl-terminal amino acids in PME-1 binding, amino acids other than those at the extreme carboxyl terminus of the C subunit also play an important role in PME-1 binding to a catalytically inactive mutant. (+info)
A new carboxylesterase from Brevibacterium linens IFO 12171 responsible for the conversion of 1,4-butanediol diacrylate to 4-hydroxybutyl acrylate: purification, characterization, gene cloning, and gene expression in Escherichia coli.
(14/1703)A carboxylesterase that is responsible for conversion of 1,4-butanediol diacrylate (BDA) to 4-hydroxybutyl acrylate (4HBA) was found in Brevibacterium lines IFO 12171, and purified to homogeneity. The purified enzyme was active toward a variety of diesters of ethylene glycol, 1,4-butanediol, and 1,6-hexanediol. The K(m) and kcat of the enzyme for BDA were 3.04 mM and 203,000 s-1, respectively. The reaction with the purified enzyme gave 98 mM 4HBA from 100 mM BDA for 60 min. The enzyme gene was cloned from the chromosomal DNA of the bacterium. The open reading frame encoding the enzyme was 1176 bp long, corresponding to a protein of 393 amino acid residues (molecular mass = 42,569 Da). The deduced amino acid sequence contained the tetra peptide motif sequence, STTK, and the serine residue was confirmed to be the catalytic center of BDA esterase by site-directed mutagenesis for several amino acid residues. The gene was expressed in Escherichia coli under the control of the lac promoter, and the gene product (a fusion protein with 6 amino acid residues from beta-galactosidase) showed the same catalytic properties as the enzyme from the parent strain. (+info)
Effect of pectin methylesterase gene expression on pea root development.
(15/1703)Expression of an inducible gene with sequences common to genes encoding pectin methylesterase (PME) was found to be tightly correlated, both spatially and temporally, with border cell separation in pea root caps. Partial inhibition of the gene's expression by antisense mRNA in transgenic pea hairy roots prevented the normal separation of root border cells from the root tip into the external environment. This phenotype was correlated with an increase in extracellular pH, reduced root elongation, and altered cellular morphology. The translation product of the gene exhibited PME activity in vitro. These results are consistent with the long-standing hypothesis that the demethylation of pectin by PME plays a key role in cell wall metabolism. (+info)
Inactivation and loss of antigenicity of esterase by sugars and a steroid.
(16/1703)Glycation, the non-enzymic reaction of sugars with proteins, has an important role in the complications of diabetes. It has been studied mostly in structural proteins but more recently has been shown to inactivate enzymes. Previous evidence from our laboratory indicated that glycation-induced inactivation and loss of antigenicity of catalase and superoxide dismutase are simultaneous. Esterase, which decreases activity in the lens in senile cataract and diabetes, was measured by a spectrophotometric assay using p-nitrophenyl acetate as the substrate. Here we investigated the inactivation of carboxylesterase (EC 220.127.116.11) by sugars of different glycating power and prednisolone-21-hemisuccinate while simultaneously monitoring the loss of antigenicity. Antigenicity was assessed by immunoprecipitation and by dot-blotting the glycated and non-glycated fractions of enzymes separated by affinity chromatography. Ribose and fructose inactivated more rapidly than glucose and glucose 6-phosphate. The esterase was progressively inactivated by prednisolone-21-hemisuccinate at a lower concentration. Activity and antigenicity were lost simultaneously. The glycated enzyme had entirely lost its antigenicity. These results further support the idea that inactivation of enzyme and loss of antigenicity are simultaneous. (+info)