A case of myasthenia gravis proven by ultrastructural study

Although light microscopic features of muscle are not pathognomonic in most cases of myasthenia gravis (MG), careful examination of neuromuscular junction by electron microscopy (EM) can reveal important clues for this disease. We report here a case of MG confirmed by EM study to emphasize that tissue diagnosis is still the best adjuvant to confirm the diagnosis. An 18-year-old female visited our hospital complaining of progressive muscle weakness for 3 years. She had difficulty in running, going upstairs and doing routine activities. Symptoms were aggravated with continuous work and resolved after rest. She had weakness of bilateral masseter and facial muscles and proximal portions of extremities without definite diurnal variation. Electromyography showed myopathic changes in proximal muscles of extremities. MG was considered but tensilon test was equivocal. Repetitive nerve stimulation tests revealed 20-30 percent decrease in responses to low and high rate stimulation. Muscle biopsy revealed selective type 2 atrophy. Ultrastructurally, abnormalities of neuromuscular junctions, i.e., wide primary synaptic cleft, and wide and shallow secondary synaptic clefts with mild myopathic features were present. These findings were pathognomonic for MG. Later, her symptoms were improved completely 3 months after thymectomy. The histologic finding of thymus was follicular hyperplasia.

Synchronization of evoked secretion of quanta of mediator as a mechanism facilitating the action of sympathomimetics

Experiments on frog neuromuscular junction preparations with extracellular recording of nerve terminal action potentials and single-quantum end-plate currents (EPC) were used to assess the time course of evoked quantum secretion of mediator by analyzing histograms of the distribution of true synaptic delays. These studies showed that noradrenaline, isoproterenol, and dobutamine change the kinetics of secretion of quanta, leading to synchronization of the process of mediator release; substances blocking beta-adrenoceptors (atenolol, propranolol) blocked this effect. Clonidine and phenylephrine, which activate alpha-receptors, had no effect on the kinetics of secretion, while the alpha-blocker phentolamine had no effect on the synchronizing action of noradrenaline. Reconstruction of multiquantum EPC from changes in the level of synchronization in the release of individual quanta, showed that EPC amplitude increased in response to noradrenaline by 17%, and that this was due only to alterations in the time course of secretion. These data led to the conclusion that there is a special presynaptic mechanism which facilitates the action of sympathomimetics, acting via beta-adrenoceptors.

Identification of a brain specific protein that associates with a refsum disease gene product, phytanoyl-CoA alpha-hydroxylase

Refsum disease is an autosomal recessive neurologic disorder of the lipid metabolism. Major diagnostic clinical findings include retinitis pigmentosa, peripheral polyneuropathy, cerebellar ataxia, increased cerebrospinal fluid protein without pleocytosis, nerve deafness, and cardiac involvement. We have identified a novel protein (PAHX-AP #1) associated with phytanoyl-CoA alpha-hydroxylase (PAHX), a Refsum disease gene product, using the yeast-based two-hybrid assay. The middle portion (amino acids 83-264) of PAHX was used as a bait and a mouse brain cDNA library was searched. The ability of PAHX-AP #1 to interact with PAHX was confirmed using immunoprecipitation and Western blot studies in NIH3T3 cells which stably expressed both PAHX and PAHX-AP #1. Northern and Western blot analyses demonstrated a unique pattern of developmental PAHX-AP #1 expression which was targeted to the adult brain, but ubiquitous expressions of PAHX were observed in all examined tissues. In situ hybridization analyses of the brain showed specific localization of PAHX-AP #1 to the supragranular layer in the cerebral cortex, dentate gyrus, hippocampus, Purkinje cell layer, deep cerebellar nucleus, trigeminal nucleus, abducent nucleus, facial nucleus, cochlear and vestibular nucleus, ganglion cell and nuclear layer of the retina. These data indicate that localization of PAHX-AP #1 in the brain is correlated with central neurologic symptoms of Refsum disease such as retinitis pigmentosa, cerebellar ataxia, nerve deafness and suggest that PAHX-AP #1 may be involved in the development of the central neurologic deficits of Refsum disease.

Isolation and identification of antifungal N-butylbenzenesulphonamide produced by Pseudomonas sp. AB2

An antifungal bacterial strain, isolated from a greenhouse soil sample, inhibits growth of microflora nearby. It was selected for further studies of bacterial antifungal properties. This isolate was identified as a Pseudomonas sp. based on carbohydrate utilization, and other biochemical and physiological tests. Petri plate assay revealed that the Pseudomonas sp. exhibited antifungal activity against the plant pathogens, Pythium ultimum, Rhizoctonia solani, Phytophthora capsici, Botrytis cinerea and Fusarium oxysporum. Using direct inhibition bioassay on TLC plates after ethyl acetate extraction of the culture filtrate, we correlated antifungal activity with production of antifungal compounds. An antifungal antibiotic was isolated from the culture filtrate and was identified as N-butylbenzenesulphonamide. ED50, values of the N-butylbenzenesulphonamide against P. ultimum, P. capsici, R. solani, and B. cinerea were 73, 41, 33 and 102 ppm, respectively.

Crystal structure of a fibrillarin homologue from Methanococcus jannaschii, a hyperthermophile, at 1.6 A resolution

Fibrillarin is a phylogenetically conserved protein essential for efficient processing of pre-rRNA through its association with a class of small nucleolar RNAs during ribosomal biogenesis. The protein is the antigen for the autoimmune disease scleroderma. Here we report the crystal structure of the fibrillarin homologue from Methanococcus jannaschii, a hyperthermophile, at 1.6 A resolution. The structure consists of two domains, with a novel fold in the N-terminal region and a methyltransferase-like domain in the C-terminal region. Mapping temperature-sensitive mutations found in yeast fibrillarin Nop1 to the Methanococcus homologue structure reveals that many of the mutations cluster in the core of the methyltransferase-like domain.

Crystallization and preliminary crystallographic studies of ribosome recycling factor from Escherichia coli

Ribosome recycling factor (RRF) catalyzes the disassembly of a termination complex during the final stage of protein synthesis. RRF from Escherichia coli has been crystallized with PEG 400 as precipitant at 287 K. The crystal belongs to the trigonal space group P3(1)21 (or P3(2)21), with unit-cell parameters a = b = 48.08, c = 141.67 A. Native data were collected from a frozen crystal to a resolution of 3.0 A on a Cu Kalpha rotating-anode X-ray source.

Prognostic factors in anterior temporal lobe resections for mesial temporal lobe epilepsy: multivariate analysis

PURPOSE

Even though there have been several studies on the prognostic factors of temporal lobe epilepsy (TLE) after lobectomy, no studies have been performed for homogeneous mesial TLE. Furthermore, most studies on the predictors of outcome of epileptic surgery were based on univariate analyses and did not consider modern epileptic surgery investigation modalities such as brain magnetic resonance imaging (MRI) and positron emission tomography (PET). We attempted to identify the prognostic factors in anterior temporal lobectomy (ATL) for mesial TLE with multivariate analysis.

METHODS

Ninety-three patients with mesial TLE (54 men and 39 women, mean age at surgery, 28.3 +/- 8.2 years) were included in the study. The primary outcome variable was the status of patients in the second postoperative year, classified as either seizure free (except aura), or not seizure free. Clinical, electroencephalographic, MRI, PET, Wada test, and pathological data were considered.

RESULTS

Seventy-eight (84.0%) patients had remission of seizures. With univariate analysis, age at surgery (p < 0.001), epilepsy duration before surgery (p = 0.04), and ipsilateral hippocampal sclerosis on MRI (p = 0.02) were found to be significant. By using multivariate analysis, age at surgery (p = 0.001) and ipsilateral hippocampal sclerosis on MRI (p = 0.03) were found to be the most significant prognostic factors.

CONCLUSIONS

Age at surgery and hippocampal sclerosis are independent prognostic factors for ATL in mesial TLE. These findings suggest that mesial TLE may be a progressive disorder, and surgical outcome is better when early ATL is performed.

Increase in extracellular glutatione peroxidase in plasma and lungs of mice exposed to hyperoxia

Extracellular glutathione peroxidase (E-GPx) is a selenium-dependent enzyme that can reduce hydrogen peroxide and phospholipid hydroperoxides. E-GPx is found in plasma and extracellular fluids such as bronchoalveolar lavage fluid. Because lung is one of the tissues that is capable of synthesizing and secreting E-GPx, the effect of exposure to hyperoxia on E-GPx in plasma and lung were studied in an injury model of hyperoxia exposure in adult mice. Exposure to 100% oxygen for 72 h resulted in an increase of 55% in plasma GPx activity and an increase of 50% in the amount of E-GPx protein in the plasma. Exposure to hyperoxia was also associated with an increase in the amount of E-GPx protein in lungs. The 7-fold increase in the amount of E-GPx protein in lungs was not due to plasma contamination of lungs from mice exposed to hyperoxia. E-GPx in the lung is calculated to account for 10% of lung GPx activity in control mice. However, E-GPx is calculated to account for 45% of lung GPx activity in the lungs of mice exposed to hyperoxia for 72 h. Further studies are needed to determine whether the increase in lung E-GPx is due to changes in translation or stability of E-GPx. The role of E-GPx in protecting the lung from oxidative damage warrants further study.

Four-helical-bundle structure of the cytoplasmic domain of a serine chemotaxis receptor

The bacterial chemotaxis receptors are transmembrane receptors with a simple signalling pathway which has elements relevant to the general understanding of signal recognition and transduction across membranes, how signals are relayed between molecules in a pathway, and how adaptation to a persistent signal is achieved. In contrast to many mammalian receptors which signal by oligomerizing upon ligand binding, the chemotaxis receptors are dimeric even in the absence of their ligands, and their signalling does not depend on a monomer-dimer equilibrium. Bacterial chemotaxis receptors are composed of a ligand-binding domain, a transmembrane domain consisting of two helices TM1 and TM2, and a cytoplasmic domain. All known bacterial chemotaxis receptors have a highly conserved cytoplasmic domain, which unites signals from different ligand domains into a single signalling pathway to flagella motors. Here we report the crystal structure of the cytoplasmic domain of a serine chemotaxis receptor of Escherichia coli, which reveals a 200 A-long coiled-coil of two antiparallel helices connected by a 'U-turn'. Two of these domains form a long, supercoiled, four-helical bundle in the cytoplasmic portion of the receptor.

Molecular cloning and characterization of splice variants of human RAD50 gene

In this report, splice variants of human RAD50 (hRAD50) were cloned and characterized. A Northern blot survey identified two transcripts that hybridized to a hRAD50 cDNA clone, an upper faint band (5.9kb) and lower dense band (4.6kb). cDNA clones (hRAD50-2, 4.6kb) encompassing the entire hRAD50 transcript but having a shorter 3'-untranslated region (3'UTR) than the previously reported hRAD50-1 cDNA (5.9kb; Dolganov, G.M., Maser, R.S., Novikov, A., Tosto, L., Chong, S., Bressan, D.A., Petrini, J.H.J., 1996. Human Rad50 is physically associated with human Mre11: Identification of a conserved multiprotein complex implicated in recombinational DNA repair. Mol. Cell. Biol. 16, 4832-4841.) were isolated. The presence of AU-rich sequences in the 3'UTR of hRAD50-1, which define mRNA instability and Northern results, suggest that hRAD50-2 is the major transcript of hRAD50. A third alternative splice variant that lacks the ATP-binding domain was also identified (hRAD50-3, approximately 4.5kb). Expression of hRAD50-3 transcript was detected in all tissues examined by RT-PCR (reverse transcriptase-polymerase chain reaction) and nested DNA-PCR analyses. Expression of hRAD50 partially rescued the MMS (methyl methanesulfonate)-sensitive phenotype in rad50 mutant yeast, whereas hRAD50-3 did not show complementation. These data suggest that the hRAD50-3 does not repair DNA double-strand breaks most likely due to its inability to bind ATP, and to bind damaged DNA. The existence of these alternative splice forms is potentially important in regulation of the biological activity of the DNA recombinational repair gene, hRAD50.

Button battery impaction in nasal cavity

A button battery inserted in the nose of children is an unusual foreign body which is capable of causing extensive tissue damage, resulting from electrical and chemical burns. We report a case of button battery in the nose of a 4-year-old boy presenting with unilateral nasal discharge, and necrosis in the septum and turbinate of the right nasal cavity. Mercury level in concentrated urine was within normal limit. Microscopic examination disclosed extensive liquefaction necrosis with calcification and fibrosis. Numerous dark brown to black granules were noted in the elastic and collagen fibers and interstitium. Dark-field examination of the section revealed brilliantly refractile granules. Polarized microscopy failed to show the granules. Most brown pigments reacted to prussian blue. Tissue mercury analysis yielded a mercury content of 8.01 ppm. We report this case to emphasize the hazards of button battery impaction and to draw attention to the significance of the problem through histopathologic examination.

Ileal obstruction caused by idiopathic sclerosing encapsulating peritonitis

A 26-year-old woman presented with epigastric pain, vomiting, and a palpable mass in the right lower abdomen. Ultrasonography showed a high echogenic mass associated with a small amount of ascites in the right lower abdomen. Computed tomography demonstrated entrapped ileal loops within a thin-walled fibrous capsule. A thin fibrous sac encasing the terminal ileum was detected on laparotomy and confirmed as idiopathic sclerosing encapsulating peritonitis.

Structure-based assignment of the biochemical function of a hypothetical protein: a test case of structural genomics

Many small bacterial, archaebacterial, and eukaryotic genomes have been sequenced, and the larger eukaryotic genomes are predicted to be completely sequenced within the next decade. In all genomes sequenced to date, a large portion of these organisms' predicted protein coding regions encode polypeptides of unknown biochemical, biophysical, and/or cellular functions. Three-dimensional structures of these proteins may suggest biochemical or biophysical functions. Here we report the crystal structure of one such protein, MJ0577, from a hyperthermophile, Methanococcus jannaschii, at 1.7-A resolution. The structure contains a bound ATP, suggesting MJ0577 is an ATPase or an ATP-mediated molecular switch, which we confirm by biochemical experiments. Furthermore, the structure reveals different ATP binding motifs that are shared among many homologous hypothetical proteins in this family. This result indicates that structure-based assignment of molecular function is a viable approach for the large-scale biochemical assignment of proteins and for discovering new motifs, a basic premise of structural genomics.

Expression of extracellular glutathione peroxidase in human and mouse gastrointestinal tract

Extracellular glutathione peroxidase (EGPx) is a glycosylated selenoprotein capable of reducing hydrogen peroxide, organic hydroperoxides, free fatty acid hydroperoxides, and phosphatidylcholine hydroperoxides. We found that human large intestinal explant cultures synthesize EGPx and cellular glutathione peroxidase (CGPx) and secrete EGPx. The level of EGPx mRNA expression relative to alpha-tubulin was similar throughout the mouse gastrointestinal tract. EGPx mRNA transcripts have been localized to mature absorptive epithelial cells in human and mouse large intestine. Western blot analysis of mouse intestinal protein has demonstrated the presence of EGPx protein in the small intestine, cecum, and large intestine, with the highest protein levels found in the cecum. Immunohistochemistry studies of human large intestine and mouse small and large intestine sections demonstrated the presence of EGPx protein within mature absorptive epithelial cells. In human large intestine and mouse small intestine, EGPx protein is also present in the extracellular milieu. These results suggest a role for EGPx in protection of the intestinal tract from peroxidative damage and/or in intercellular metabolism of peroxides.

Development and evaluation of the Osteoporosis Self-Efficacy Scale

The Osteoporosis Self-Efficacy Scale was developed as a measure of self-efficacy, or confidence, for behaviors related to physical activity and calcium intake. An item pool of 21 statements, responded to on a visual analog self-report format, was reviewed by a panel of expert judges. The revised item stems were tested with a sample of 201 women, ages 35 to 95. Concurrent data on sport, leisure, and exercise activity and calcium in diet and dietary supplements were collected from the respondents. Factor analysis of responses to the self-efficacy items revealed a logical, theoretically meaningful two-factor structure, one for physical activity and one for calcium intake. Internal consistency estimates for each of the two factors were in the .90s. Convergent and discriminant validity analyses as well as hierarchical regression analyses to explain self-reports of physical activity and calcium intake were supportive. The final version of the brief, psychometrically sound scale contains items reflecting initiation, maintenance, and persistence at osteoporosis preventive behaviors; thus, the Osteoporosis Self-Efficacy Scale is a potentially beneficial research instrument.

Crystal structures of eukaryotic translation initiation factor 5A from Methanococcus jannaschii at 1.8 A resolution

Eukaryotic translation initiation factor 5A (eIF-5A) is a ubiquitous protein found in all eukaryotic cells. The protein is closely associated with cell proliferation in the G1-S stage of the cell cycle. Recent findings show that the eIF-5A proteins are highly expressed in tumor cells and act as a cofactor of the Rev protein in HIV-1-infected cells. The mature eIF is the only protein known to have the unusual amino acid hypusine, a post-translationally modified lysine. The crystal structure of eIF-5A from Methanococcus jannaschii (MJ eIF-5A) has been determined at 1.9 A and 1.8 A resolution in two crystal forms by using the multiple isomorphous replacement method and the multiwavelength anomalous diffraction method for the first crystal form and the molecular replacement method for the second crystal form. The structure consists of two folding domains, one of which is similar to the oligonucleotide-binding domain found in the prokaryotic cold shock protein and the translation initiation factor IF1 despite the absence of any significant sequence similarities. The 12 highly conserved amino acid residues found among eIF-5As include the hypusine site and form a long protruding loop at one end of the elongated molecule.

Crystal structure of a small heat-shock protein

The principal heat-shock proteins that have chaperone activity (that is, they protect newly made proteins from misfolding) belong to five conserved classes: HSP100, HSP90, HSP70, HSP60 and the small heat-shock proteins (sHSPs). The sHSPs can form large multimeric structures and have a wide range of cellular functions, including endowing cells with thermotolerance in vivo and being able to act as molecular chaperones in vitro; sHSPs do this by forming stable complexes with folding intermediates of their protein substrates. However, there is little information available about these structures or the mechanism by which substrates are protected from thermal denaturation by sHSPs. Here we report the crystal structure of a small heat-shock protein from Methanococcus jannaschii, a hyperthermophilic archaeon. The monomeric folding unit is a composite beta-sandwich in which one of the beta-strands comes from a neighbouring molecule. Twenty-four monomers form a hollow spherical complex of octahedral symmetry, with eight trigonal and six square 'windows'. The sphere has an outer diameter of 120 A and an inner diameter of 65 A.

Small heat shock protein of Methanococcus jannaschii, a hyperthermophile

Small heat shock proteins (sHSPs) belong to a family of 12- to 43-kDa proteins that are ubiquitous and are conserved in amino acid sequence among all organisms. A sHSP homologue of Methanococcus jannaschii, a hyperthermophilic Archaeon, forms a homogeneous multimer comprised of 24 monomers with a molecular mass of 400 kDa in contrast to other sHSPs that show heterogeneous oligomeric complexes. Electron microscopy analysis revealed a spherically shaped oligomeric structure approximately 15-20 nm in diameter. The protein confers thermal protection of other proteins in vitro as found in other sHSPs. Escherichia coli cell extracts containing the protein were protected from heat-denatured precipitation when heated up to 100 degreesC, whereas extracts from cells not expressing the protein were heat-sensitive at 60 degreesC. Similar results were obtained when purified sHSP protein was added to an E. coli cell lysate. The protein also prevented the aggregation of two purified proteins: single-chain monellin (SCM) at 80 degreesC and citrate synthase at 40 degreesC.

HSP70 and ER expression in cervical intraepithelial neoplasia and cervical cancer

Heat shock protein (HSP) is thought to play important roles in the cell cycle and various process of carcinogenesis. This study was performed to evaluate the expression of heat shock protein (HSP70) and estrogen receptor (ER) and Ki-67 and to assess relationship between them in cervical squamous cell neoplasia. The materials were 50 cervical squamous cell lesions, consisted of 30 cervical intraepithelial neoplasia (CIN) (6 moderate dysplasia, 11 severe dysplasia, 13 carcinoma in situ), and 20 invasive squamous cell carcinoma (ISCC) cases. These specimens were immunohistochemically stained for HSP70, ER and Ki-67. The score of HSP70 was significantly higher in ISCC than CIN. Expression rate of the ER was not significantly higher in CIN than in ISCC. Ki-67 labelling index was significantly higher in the ISCC and high HSP70 positive staining group. These results suggested that HSP70 may play an important role in tumor cell proliferation and is related with ISCC than CIN, but ER may be not related with tumor cell proliferation and differentiation. HSP70 may be a useful prognostic factor in cervical dysplasia and cancer.

TR1, a new member of the tumor necrosis factor receptor superfamily, induces fibroblast proliferation and inhibits osteoclastogenesis and bone resorption

A newly identified member of the tumor necrosis factor receptor (TNFR) superfamily shows activities associated with osteoclastogenesis inhibition and fibroblast proliferation. This new member, called TR1, was identified from a search of an expressed sequence tag database, and encodes 401 amino acids with a 21-residue signal sequence. Unlike other members of TNFR, TR1 does not contain a transmembrane domain and is secreted as a 62 kDa glycoprotein. TR1 gene maps to chromosome 8q23-24.1 and its mRNA is abundantly expressed on primary osteoblasts, osteogenic sarcoma cell lines, and primary fibroblasts. The receptors for TR1 were detected on a monocytic cell line (THP-1) and in human fibroblasts. Scatchard analyses indicated two classes of high and medium-high affinity receptors with a kD of approximately 45 and 320 pM, respectively. Recombinant TR1 induced proliferation of human foreskin fibroblasts and potentiated TNF-induced proliferation in these cells. In a coculture system of osteoblasts and bone marrow cells, recombinant TR1 completely inhibited the differentiation of osteoclast-like multinucleated cell formation in the presence of several bone-resorbing factors. TR1 also strongly inhibited bone-resorbing function on dentine slices by mature osteoclasts and decreased 45Ca release in fetal long-bone organ cultures. Anti-TR1 monoclonal antibody promoted the formation of osteoclasts in mouse marrow culture assays. These results indicate that TR1 has broad biological activities in fibroblast growth and in osteoclast differentiation and its functions.

Electron transfer by domain movement in cytochrome bc1

The cytochrome bc1 is one of the three major respiratory enzyme complexes residing in the inner mitochondrial membrane. Cytochrome bc1 transfers electrons from ubiquinol to cytochrome c and uses the energy thus released to form an electrochemical gradient across the inner membrane. Our X-ray crystal structures of the complex from chicken, cow and rabbit in both the presence and absence of inhibitors of quinone oxidation, reveal two different locations for the extrinsic domain of one component of the enzyme, an iron-sulphur protein. One location is close enough to the supposed quinol oxidation site to allow reduction of the Fe-S protein by ubiquinol. The other site is close enough to cytochrome c1 to allow oxidation of the Fe-S protein by the cytochrome. As neither location will allow both reactions to proceed at a suitable rate, the reaction mechanism must involve movement of the extrinsic domain of the Fe-S component in order to shuttle electrons from ubiquinol to cytochrome c1. Such a mechanism has not previously been observed in redox protein complexes.

Reduction in transforming growth factor beta receptor I expression and transcription factor CBFa1 on bone cells by glucocorticoid

Glucocorticoid in excess suppresses bone formation in vivo and disrupts bone matrix protein synthesis by osteoblasts in vitro. In contrast, transforming growth factor beta (TGF-beta) potently enhances bone matrix apposition. The rat TGF-beta type I receptor gene promoter contains cis-acting elements for transcription factor CBFa1, which increases in parallel with osteoblast differentiation. Here we present molecular data linking these events. We show that previously unexplained effects of glucocorticoid on bone loss may be mediated in part by suppression of CBFa1, with a resultant decrease in the expression and activity of the TGF-beta type I receptor on matrix-producing bone cells.

Purification, crystallization, and preliminary X-ray crystallographic data analysis of small heat shock protein homolog from Methanococcus jannaschii, a hyperthermophile

A gene coding for a small heat shock protein homolog from the hyperthermophilic methanogenic Archaeon Methanococcus jannaschii was cloned. This gene was overexpressed in Escherichia coli harboring rare codon tRNAs and its protein purified and crystallized. Crystals displayed the space group R3 with unit cell dimensions a = b = 171.46 A and c = 102.13 A in a hexagonal axis setting. These crystals grew in one week and diffracted to 3.2 A resolution. The presence of eight molecules in the asymmetric unit gives a Vm value of 2.2 A3/Da and a solvent content of 44% by volume. The 24-molecule complex is generated from a subunit by a combination of crystallographic threefold symmetry and three types of noncrystallographic symmetries (a two-, a three-, and a fourfold).

Crystal structure of carboxylesterase from Pseudomonas fluorescens, an alpha/beta hydrolase with broad substrate specificity

BACKGROUND

A group of esterases, classified as carboxylesterases, hydrolyze carboxylic ester bonds with relatively broad substrate specificity and are useful for stereospecific synthesis and hydrolysis of esters. One such carboxylesterase from Pseudomonas fluorescens is a homodimeric enzyme, consisting of 218-residue subunits. It shows a limited sequence similarity to some members of the alpha/beta hydrolase superfamily. Although crystal structures of a number of serine esterases and lipases have been reported, structural information on carboxylesterases is very limited. This study was undertaken in order to provide such information and to understand a structural basis for the substrate specificity of this carboxylesterase.

RESULTS

In this study, the crystal structure of carboxylesterase from P. fluorescens has been determined by the isomorphous replacement method and refined to 1.8 A resolution. Each subunit consists of a central seven-stranded beta sheet flanked by six alpha helices. The structure reveals the catalytic triad as Ser 114-His 199-Asp 168. The structure of the enzyme in complex with the inhibitor phenylmethylsulfonyl fluoride has also been determined and refined to 2.5 . The inhibitor is covalently attached to Ser 114 of both subunits, with the aromatic ring occupying a hydrophobic site defined by the aliphatic sidechains of Leu23, Ile58, Ile70, Met73 and Val170. No large structural changes are observed between the free and inhibitor-bound structures.

CONCLUSIONS

Carboxylesterase from P. fluorescens has the alpha/beta hydrolase fold and the Ser-His-Asp catalytic triad. The active-site cleft in each subunit is formed by the six loops covering the catalytic serine residue. Three of the active-site loops in each subunit are involved in a head-to-head subunit interaction to form a dimer; it may be these extra structural elements, not seen in other esterases, that account for the inability of carboxylesterase to hydrolyze long chain fatty acids. As a result of dimerization, the active-site clefts from the two subunits merge to form holes in the dimer. The active-site clefts are relatively open and thus the catalytic residues are exposed to the solvent. An oxyanion hole, formed by nitrogen atoms of Leu23 and Gln115, is present in both the free and inhibitor-bound structures. An open active site, as well as a large binding pocket for the acid part of substrates, in P. fluorescens carboxylesterase may contribute to its relatively broad substrate specificity.

Molecular cloning of leukotactin-1: a novel human beta-chemokine, a chemoattractant for neutrophils, monocytes, and lymphocytes, and a potent agonist at CC chemokine receptors 1 and 3

A new member of human beta-chemokine cDNA was isolated and named leukotactin-1 (Lkn-1). Lkn-1, along with murine macrophage inflammatory protein-related protein-1 and -2, defines a subgroup of beta-chemokines based on two conserved cysteines in addition to the four others conserved in all beta-chemokines. The putative mature Lkn-1 is composed of 92 amino acids with a calculated m.w. of 10,162. The Lkn-1 gene was mapped to human chromosome 17, region q12. Recombinant Lkn-1 was a potent chemoattractant for neutrophils, monocytes, and lymphocytes and induced calcium flux in these cells. Lkn-1 specifically induced calcium flux in CCR1- and CCR3-expressing HOS cell lines. Lkn-1 suppressed colony formation by human granulocyte-macrophage, erythroid, and multipotential progenitor cells stimulated by combinations of growth factors. Hence, we have isolated and characterized a human C6 beta-chemokine that is a potent agonist at CCR1 and CCR3 and shows broad biologic activities, including leukocyte chemoattraction.