Identification of proteins associated with adhesive prints from Holothuria dofleinii Cuvierian tubules

Cuvierian tubules are expelled as a defence mechanism against predators by various species within the family Holothuridae. When the tubules are expelled, they become sticky almost immediately and ensnare the predator. The mechanism of this rapid adhesion is not clear, but proteins on the surface of the expelled tubules are widely believed to be involved. This study has examined such proteins from Holothuria dofleinii, sourced from adhesive prints left on glass after the removal of adhered tubules. Gel electrophoresis showed that seven strongly staining protein bands were consistently present in all samples, with molecular masses ranging from 89 to 17 kDa. N-terminal sequence data was obtained from two bands, while others seemed blocked. Tandem mass spectrometry-based sequencing of tryptic peptides derived from individual protein bands indicated that the proteins were unlikely to be homopolymers. PCR primers designed using the peptide sequences enabled us to amplify, clone and sequence cDNA segments relating to four gel bands; for each, the predicted translation product contained other peptide sequences observed for that band that had not been used in primer design. Database searches using the peptide and cDNA-encoded sequences suggest that two of the seven proteins are novel and one is a C-type lectin, while-surprisingly-at least three of the other four are closely related to enzymes associated with the pentose phosphate cycle and glycolysis. We discuss precedents in which lectins and metabolic enzymes are involved in attachment and adhesion phenomena.

Unprecedented conformational flexibility revealed in the ligand-binding domains of theBovicola ovisecdysone receptor (EcR) and ultraspiracle (USP) subunits

The heterodimeric ligand-binding region of theBovicola ovisecdysone receptor has been crystallized either in the presence of an ecdysteroid or a synthetic methylene lactam insecticide. Two X-ray crystallographic structures, determined at 2.7 Å resolution, show that the ligand-binding domains of both subunits of this receptor, like those of other nuclear receptors, can display significant conformational flexibility. Thermal melt experiments show that while ponasterone A stabilizes the higher order structure of the heterodimer in solution, the methylene lactam destabilizes it. The conformations of the EcR and USP subunits observed in the structure crystallized in the presence of the methylene lactam have not been seen previously in any ecdysone receptor structure and represent a new level of conformational flexibility for these important receptors. Interestingly, the new USP conformation presents an open, unoccupied ligand-binding pocket.

CAHM, a long non-coding RNA gene hypermethylated in colorectal neoplasia

The CAHM gene (Colorectal Adenocarcinoma HyperMethylated), previously LOC100526820, is located on chromosome 6, hg19 chr6:163 834 097–163 834 982. It lacks introns, encodes a long non-coding RNA (lncRNA) and is located adjacent to the gene QKI, which encodes an RNA binding protein. Deep bisulphite sequencing of ten colorectal cancer (CRC) and matched normal tissues demonstrated frequent hypermethylation within the CAHM gene in cancer. A quantitative methylation-specific PCR (qMSP) was used to characterize additional tissue samples. With a threshold of 5% methylation, the CAHM assay was positive in 2/26 normal colorectal tissues (8%), 17/21 adenomas (81%), and 56/79 CRC samples (71%). A reverse transcriptase-qPCR assay showed that CAHM RNA levels correlated negatively with CAHM % methylation, and therefore CAHM gene expression is typically decreased in CRC. The CAHM qMSP assay was applied to DNA isolated from plasma specimens from 220 colonoscopy-examined patients. Using a threshold of 3 pg methylated genomic DNA per mL plasma, methylated CAHM sequences were detected in the plasma DNA of 40/73 (55%) of CRC patients compared with 3/73 (4%) from subjects with adenomas and 5/74 (7%) from subjects without neoplasia. Both the frequency of detection and the amount of methylated CAHM DNA released into plasma increased with increasing cancer stage. Methylated CAHM DNA shows promise as a plasma biomarker for use in screening for CRC.

CRNDE, a long non-coding RNA responsive to insulin/IGF signaling, regulates genes involved in central metabolism

Colorectal neoplasia differentially expressed (CRNDE) is a novel gene that is activated early in colorectal cancer but whose regulation and functions are unknown. CRNDE transcripts are recognized as long non-coding RNAs (lncRNAs), which potentially interact with chromatin-modifying complexes to regulate gene expression via epigenetic changes. Complex alternative splicing results in numerous transcripts from this gene, and we have identified novel transcripts containing a highly-conserved sequence within intron 4 ("gVC-In4"). In colorectal cancer cells, we demonstrate that treatment with insulin and insulin-like growth factors (IGF) repressed CRNDE nuclear transcripts, including those encompassing gVC-In4. These repressive effects were negated by use of inhibitors against either the PI3K/Akt/mTOR pathway or Raf/MAPK pathway, suggesting CRNDE is a downstream target of both signaling cascades. Expression array analyses revealed that siRNA-mediated knockdown of gVC-In4 transcripts affected the expression of many genes, which showed correlation with insulin/IGF signaling pathway components and responses, including glucose and lipid metabolism. Some of the genes are identical to those affected by insulin treatment in the same cell line. The results suggest that CRNDE expression promotes the metabolic changes by which cancer cells switch to aerobic glycolysis (Warburg effect). This is the first report of a lncRNA regulated by insulin/IGFs, and our findings indicate a role for CRNDE nuclear transcripts in regulating cellular metabolism which may correlate with their upregulation in colorectal cancer.

The adhesive skin exudate of Notaden bennetti frogs (Anura: Limnodynastidae) has similarities to the prey capture glue of Euperipatoides sp. velvet worms (Onychophora: Peripatopsidae)

The dorsal adhesive secretion of the frog Notaden bennetti and the prey-capture "slime" ejected by Euperipatoides sp. velvet worms look and handle similarly. Both consist largely of protein (55-60% of dry weight), which provides the structural scaffold. The major protein of the onychophoran glue (Er_P1 for Euperipatoides rowelli) and the dominant frog glue protein (Nb-1R) are both very large (260-500 kDa), and both give oddly "turbulent" electrophoresis bands. Both major proteins, which are rich in Gly (16-17 mol%) and Pro (7-12 mol%) and contain 4-hydroxyproline (Hyp, 4 mol%), have the composition of intrinsically unstructured proteins. Their propensities for elastomeric or amyloid structures are discussed in light of Er_P1's large content of intrinsically disordered long tandem repeats. The low carbohydrate content of both glues is consistent with conventional protein glycosylation, which in the N. bennetti adhesive was explored by 2D PAGE. The N-linked sugars of Nb-1R appear to prevent inappropriate self-aggregation. Some peptide sequences from Nb-1R are presented. Overall, there are enough similarities between the frog and the velvet worm glues to suspect that they employ related mechanisms for setting and adhesion. A common paradigm is proposed for amphibian and onychophoran adhesives, which, if correct, points to convergent evolution.

CRNDE: A Long Non-Coding RNA Involved in CanceR, Neurobiology, and DEvelopment

CRNDE is the gene symbol for Colorectal Neoplasia Differentially Expressed (non-protein-coding), a long non-coding RNA (lncRNA) gene that expresses multiple splice variants and displays a very tissue-specific pattern of expression. CRNDE was initially identified as a lncRNA whose expression is highly elevated in colorectal cancer, but it is also upregulated in many other solid tumors and in leukemias. Indeed, CRNDE is the most upregulated lncRNA in gliomas and here, as in other cancers, it is associated with a "stemness" signature. CRNDE is expressed in specific regions within the human and mouse brain; the mouse ortholog is high in induced pluripotent stem cells and increases further during neuronal differentiation. We suggest that CRNDE is a multifunctional lncRNA whose different splice forms provide specific functional scaffolds for regulatory complexes, such as the polycomb repressive complex 2 (PRC2) and CoREST chromatin-modifying complexes, which CRNDE helps pilot to target genes.

Ecdysone receptors: from the Ashburner model to structural biology

In 1974, Ashburner and colleagues postulated a model to explain the control of the puffing sequence on Drosophila polytene chromosomes initiated by the molting hormone 20-hydroxyecdysone. This model inspired a generation of molecular biologists to clone and characterize elements of the model, thereby providing insights into the control of gene networks by steroids, diatomic gases, and other small molecules. It led to the first cloning of the EcR subunit of the heterodimeric EcR-USP ecdysone receptor. X-ray diffraction studies of the ligand-binding domain of the receptor are elucidating the specificity of receptor-ecdysteroid interactions, the selectivity of some environmentally friendly insecticides, the evolution of the EcR-USP heterodimer, and indeed Ashburner's classical biochemical evidence for the central role of the ecdysone receptor in his model.

Colorectal Neoplasia Differentially Expressed (CRNDE), a Novel Gene with Elevated Expression in Colorectal Adenomas and Adenocarcinomas

An uncharacterized gene locus (Chr16:hCG_1815491), now named colorectal neoplasia differentially expressed (gene symbol CRNDE), is activated early in colorectal neoplasia. The locus is unrelated to any known protein-coding gene. Microarray analysis of 454 tissue specimens (discovery) and 68 previously untested specimens (validation) showed elevated expression of CRNDE in >90% of colorectal adenomas and adenocarcinomas. These findings were confirmed and extended by exon microarray studies and RT-PCR assays. CRNDE transcription start sites were identified in CaCo2 and HCT116 cells by 5'-RACE. The major transcript isoforms in colorectal cancer (CRC) cell lines and colorectal tissue are CRNDE-a, -b, -d, -e, -f, -h, and -j. Except for CRNDE-d, the known CRNDE splice variants are upregulated in neoplastic colorectal tissue; expression levels for CRNDE-h alone demonstrate a sensitivity of 95% and specificity of 96% for adenoma versus normal tissue. A quantitative RT-PCR assay measuring CRNDE-h RNA levels in plasma was (with a threshold of 2(-ΔCt) = 2.8) positive for 13 of 15 CRC patients (87%) but only 1 of 15 healthy individuals (7%). We conclude that individual CRNDE transcripts show promise as tissue and plasma biomarkers, potentially exhibiting high sensitivity and specificity for colorectal adenomas and cancers.

Isoforms of the heteropteran Nezara viridula ecdysone receptor: protein characterisation, RH5992 insecticide binding and homology modelling

BACKGROUND

Certain bisacylhydrazine compounds such as tebufenozide (RH5992) have been shown to act as order-specific insecticides. Their compatibility with predatory Heteroptera, which are used as biological control agents, has also been demonstrated. However, the molecular mode of action of these ecdysone agonists has not been explored in a heteropteran, much less one that is a significant agricultural pest, such as Nezara viridula.

RESULTS

Alternatively spliced ligand-binding regions of the N. viridula ecdysone receptor were expressed, purified and characterised by 2D gel analysis, mass spectrometry, homology modelling and competitive binding of a bisacylhydrazine insecticidal compound (RH5992) and various ecdysteroids. Ligand binding by the two splice isoforms was indistinguishable, and relative affinities were found to occur in the order muristerone A > ponasterone A > 20-hydroxyecdysone > inokosterone > RH5992 > α-ecdysone.

CONCLUSION

The predicted difference in amino acid sequence between the ligand-binding domains of the N. viridula ecdysone receptor splice variants was verified by mass spectrometry. Both splice variant isoforms exhibit a greater affinity for the bisacylhydrazine insecticide RH5992 than do the other hemipteran ecdysone receptors characterised to date. Their affinities for a range of ecdysteroids also distinguish them from the ecdysone receptors of other Hemiptera characterised thus far. Homology models of both N. viridula receptor isoforms provide further insight into the bisacylhydrazine- and ecdysteroid-binding properties of these receptors, including their similar affinity for 20-hydroxyecdysone and the postulated pentatomomorphan moulting hormone makisterone A.

An ecdysone receptor from the pentatomomorphan, Nezara viridula, shows similar affinities for moulting hormones makisterone A and 20-hydroxyecdysone

It has been suggested that Pentatomomorpha utilise the C(28) ecdysteroid, makisterone A (MakA), as the major moulting hormone rather than the more common C(27) hormone, 20-hydroxyecdsyone (20E). The present study is the first to examine this postulate at the level of the ecdysone receptor protein, a heterodimer of nuclear receptors EcR and USP. cDNAs encoding two alternatively spliced isoforms of EcR and a single USP were isolated from a high-quality cDNA library prepared from a representative pentatomomorphan, Nezara viridula (Nv). NvEcR and NvUSP were found to group phylogenetically with heteropteran and other insect EcRs and USP/RXRs, respectively. Sequence comparison and phylogenetic analysis of these proteins found them to be distinct from those belonging to other hemipteran ecdysone receptors characterised to date. Co-expression of the His(6)-tagged ligand binding regions (LBRs) of the two NvEcR variants with the FLAG-tagged LBR of NvUSP was achieved in insect cells employing appropriately constructed baculoviruses. The corresponding heterodimers, designated NvE10 and NvE11, were purified by affinity chromatography utilising the His(6) tags on their NvEcR subunits. The heterodimers displayed nanomolar affinity for [(3)H]ponasterone A (K(d) = 6.8-7.5 nM), characteristic of ecdysone receptors. MakA has a similar affinity to 20E for both NvE10 and NvE11, consistent with MakA being a major moulting hormone in N. viridula.

Biocompatibility and modification of the protein-based adhesive secreted by the Australian frog Notaden bennetti

When provoked, Notaden bennetti frogs secrete a proteinaceous exudate, which rapidly forms a tacky and elastic glue. This material has potential in biomedical applications. Cultured cells attached and proliferated well on glue-coated tissue culture polystyrene, but migrated somewhat slower than on uncoated surfaces. In organ culture, dissolved glue successfully adhered collagen-coated perfluoropolyether lenses to debrided bovine corneas and supported epithelial regrowth. Small pellets of glue implanted subcutaneously into mice were resorbed by surrounding tissues, and all of the animals made a full recovery. An initial but transient skin necrosis at the implant site was probably caused by some of the potentially toxic metabolites present in the frog secretion; these include sterols and carotenoids, as well as fatty alcohols, aldehydes, ketones, acids, and aromatic compounds. Removal of the carotenoid pigments did not significantly alter the glue's material properties. In contrast, peroxidase treatment of dissolved glue introduced unnatural crosslinks between molecules of the major protein (Nb-1R) and resulted in the formation of a soft hydrogel, which was very different to the original material.

An ortholog of the ecdysone receptor protein (EcR) from the parasitic nematode Haemonchus contortus

High concentrations (> or =4.2mM) of 20E inhibit the development of Haemonchus contortus eggs to the L3 larval stage. We report the cloning of cDNA encoding an EcR ortholog (HcEcR) from H. contortus mRNA expressed during L3. Phylogenetically, this and the putative EcR from Brugia malayi form a separate branch between arthropod EcRs and liver X receptors. Two isoforms of HcEcR differ in the inclusion/omission of a 3-residue segment in the A/B domain. Single nucleotide polymorphisms at 49 positions can be grouped into two major patterns in the A/BC segment and two in the DE/F segment. Some 35% of the highly conserved ecdysteroid-contacting residues in insect EcRs are also conserved in the HcEcR ligand binding domain, but it contains unusual residue choices at other ligand-contacting positions. Recombinant co-expression of HcEcR DE/F segments with a phthirapteran USP DE/F segment in insect cells resulted in stable proteins which did not heterodimerize or bind [(3)H]ponasterone A.

Proteinaceous adhesive secretions from insects, and in particular the egg attachment glue of Opodiphthera sp. moths

Biochemical and electrophoretic screening of 29 adhesive secretions from Australian insects identified six types that appeared to consist largely of protein. Most were involved in terrestrial egg attachment. Hydrogel glues were subjected to gravimetric analyses and assessed for overall amino acid composition. When 32 proteins in glues from eight insect species were analyzed individually, many proved to be rich in Gly, Ser, and/or Pro, and some contained substantial levels of 4-hydroxyproline. A few proteins were heavily glycosylated. Abundant protein-based secretions were tested as adhesives, mainly by measuring dry shear strength on wood. The strongest (1-2 MPa) was an egg attachment glue produced by saturniid gum moths of the genus Opodiphthera. It was harvested from female colleterial gland reservoirs as a treacle-like liquid that underwent irreversible gelation, and recovered from the capsules of laid eggs as a highly elastic orange-brown hydrogel that could also display high tack. Its protein-based nature was confirmed and explored by spectroscopy, enzymatic degradation, and 2D gel electrophoresis. Its proteins are mostly 80-95 kDa, and sequences (almost all novel) were established for 23 tryptic peptides. Scanning probe microscopy of Opodiphthera hydrogel in water returned median values of 0.83 nN for adhesion, 63 kPa for modulus, and 87% for resilience. Recombinant mimics of this material might be useful as biodegradable commodity adhesives or as specialty biomedical products.

Molecular basis of the interaction between IGFBP-3 and retinoid X receptor: role in modulation of RAR-signaling

IGFBP-3 interacts with the retinoid X receptor-alpha (RXRalpha) and retinoic acid receptor-alpha (RARalpha) and thereby interferes with the formation of RXR:RAR heterodimers. Here we identify the domains in RXRalpha and IGFBP-3 that participate in this interaction. When different regions of RXRalpha were expressed independently, we found that only the DNA-binding domain (C-domain) bound IGFBP-3. Residues in the second Zn-finger loop (Gln49, Arg52), which contribute to C-domain dimerization on DR1 response elements, proved essential to IGFBP-3 binding. In complementary studies, we found that residues within the N-terminal domain of IGFBP-3 (Thr58, Arg60) and motifs in its C-terminal domain ((220)LysLysLys, (228)LysGlyArgLysArg) were required for interaction with RXRalpha and RARalpha. Unlike wild-type IGFBP-3, the non-retinoid receptor-binding mutants of IGFBP-3 were unable to attenuate all-trans-retinoic acid-induced transactivation of the RAR response element by RXR:RAR heterodimers. We conclude that residues in both the N- and C-terminal domains of IGFBP-3 are involved in binding the retinoid receptors, and that this interaction is essential to the modulation of RAR-signaling by IGFBP-3.

Epidermal secretions of terrestrial flatworms and slugs: Lehmannia valentiana mucus contains matrilin-like proteins

We describe the epidermal mucus of two types of terrestrial invertebrates: free-living flatworms (Tricladida: Terricola), and the slug Lehmannia valentiana (Gastropoda: Pulmonata). Both exhibited similar dry shear strengths (1.4-1.7 MPa). In denaturing gel electrophoresis, the protein fraction of flatworm mucus migrated mainly as a broad band (200-300 kDa). Slug mucus had a higher protein content than flatworm mucus but it contained more carbohydrate than protein, mainly as large heparan sulfate-like glycosaminoglycans. Proteins and glycosaminoglycans were both essential for the mechanical integrity of the slug hydrogel. The protein fraction of slug mucus contained approximately 12 larger proteins (30-300 kDa) and approximately 6 smaller ones (10-28 kDa). Complete cDNA clones were obtained for the slug mucus 40 kDa protein (Sm40; Genbank accession EF634345) and 85 kDa protein (Sm85; Genbank accession EF634346). Both proteins contain EGF-like repeats and von Willebrand A-domains, and therefore resemble vertebrate matrilins. Many of the larger slug mucus proteins appear to contain A-domains, and these may play a role in the unusual rheological properties of gastropod mucus.

Ligand binding by recombinant domains from insect ecdysone receptors

The ligand binding domains (LBDs) from the EcR and USP proteins of four insect pests (Lucilia cuprina, Myzus persicae, Bemisia tabaci, Helicoverpa armigera) were purified as recombinant heterodimers. The K(d) values for [(3)H]-ponasterone A binding by LBD heterodimers that included the hinge regions (i.e., DE/F heterodimers) ranged 0.7-2.5 nM, with K(i) values for ecdysteroid and dibenzoylhydrazine ligands ranging from 0.1 nM to >448 microM. The K(d) and K(i) values for a recombinant H. armigera LBD heterodimer that lacked D-regions (i.e., an E/F heterodimer) were approximately 4 times higher than those for its DE/F counterpart. Rate constants were estimated for the L. cuprina LBD heterodimer. A fluorescein-inokosterone conjugate (K(i)~40 nM) was used to develop a novel binding assay based on fluorescence polarization. This assay, which ranked the affinity of competitor ecdysteroids in the same order as the [(3)H]-ponasterone A binding assay, is well suited to high-throughput screening. Ponasterone A had a higher affinity than muristerone A for the recombinant hemipteran LBD heterodimers, whereas the reverse was true for the recombinant dipteran one. The same preference was observed when these ligands were tested as inducers of ecdysone receptor-controlled gene expression in transfected mammalian cells. The binding data obtained in vitro using recombinant LBD heterodimers reflects the ability of agonists to induce transgene expression in recombinant mammalian cells, and can also reflect their efficacy as larvicides.

Epiphragmin, the major protein of epiphragm mucus from the vineyard snail, Cernuella virgata

The organic fraction of epiphragm mucus from the snail Cernuella virgata (Mollusca: Helicidae) consists predominantly of protein (17-23 dry wt.%) rather than carbohydrate (< or =0.4-2.0 dry wt.%), and the former underpins epiphragm membrane structure. The major protein ('epiphragmin') has an apparent molecular mass of approximately 86 kDa and is encoded by a cDNA (Genbank accession EF602752) which specifies a secreted protein of 81.2 kDa. The central region of the epiphragmin polypeptide is a coiled coil-forming region which is homologous to part of AglZ, a bacterial filament-forming protein. Coiled coil-driven self-assembly of epiphragmin probably underpins the formation of sheets in epiphragm membranes and the ability of epiphragm mucus to serve as an adhesive. The C-terminal region of epiphragmin is a fibrinogen-related domain (FReD) that is homologous to the fibrinogen-related proteins (FREPs) found in the hemolymph of freshwater snails. The material properties of epiphragm membranes resemble those of bovine ligament elastin. Wooden lap-joints bonded by rehydrated epiphragm fragments developed dry shear strength values of 1.4+/- 0.1 MPa.

Purification and characterization of recombinant ligand-binding domains from the ecdysone receptors of four pest insects

Cloned EcR and USP cDNAs encoding the ecdysone receptors of four insect pests (Lucilia cuprina, Myzus persicae, Bemisia tabaci, Helicoverpa armigera) were manipulated to allow the co-expression of their ligand binding domains (LBDs) in insect cells using a baculovirus vector. Recombinant DE/F segment pairs (and additionally, for H. armigera, an E/F segment pair) from the EcR and USP proteins associated spontaneously with high affinity to form heterodimers that avidly bound an ecdysteroid ligand. This shows that neither ligand nor D-regions are essential for the formation of tightly associated and functional LBD heterodimers. Expression levels ranged up to 16.6mg of functional apo-LBD (i.e., unliganded LBD) heterodimer per liter of recombinant insect cell culture. Each recombinant heterodimer was affinity-purified via an oligo-histidine tag at the N-terminus of the EcR subunit, and could be purified further by ion exchange and/or gel filtration chromatography. The apo-LBD heterodimers appeared to be more easily inactivated than their ligand-containing counterparts: after purification, populations of the former were <40% active, whereas for the latter >70% could be obtained as the ligand-LBD heterodimer complex. Interestingly, we found that the amount of ligand bound by recombinant LBD heterodimer preparations could be enhanced by the non-denaturing detergent CHAPS (3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propanesulfonate). Purity, integrity, size and charge data are reported for the recombinant proteins under native and denaturing conditions. Certain intra- and intermolecular disulfide bonds were observed to form in the absence of reducing agents, and thiol-specific alkylation was shown to suppress this phenomenon but to introduce microheterogeneity.

Characterization of a protein-based adhesive elastomer secreted by the Australian frog Notaden bennetti

When provoked, Notaden bennetti frogs secrete an exudate which rapidly forms a tacky elastic solid ("frog glue"). This protein-based material acts as a promiscuous pressure-sensitive adhesive that functions even in wet conditions. We conducted macroscopic tests in air to assess the tensile strength of moist glue (up to 78 +/- 8 kPa) and the shear strength of dry glue (1.7 +/- 0.3 MPa). We also performed nanomechanical measurements in water to determine the adhesion (1.9-7.2 nN or greater), resilience (43-56%), and elastic modulus (170-1035 kPa) of solid glue collected in different ways. Dry glue contains little carbohydrate and consists mainly of protein. The protein complement is rich in Gly (15.8 mol %), Pro (8.8 mol %), and Glu/Gln (14.1 mol %); it also contains some 4-hydroxyproline (4.6 mol %) but no 5-hydroxylysine or 3,4-dihydroxyphenylalanine (L-Dopa). Denaturing gel electrophoresis of the glue reveals a characteristic pattern of proteins spanning 13-400 kDa. The largest protein (Nb-1R, apparent molecular mass 350-500 kDa) is also the most abundant, and this protein appears to be the key structural component. The solid glue can be dissolved in dilute acids; raising the ionic strength causes the glue components to self-assemble spontaneously into a solid which resembles the starting material. We describe scattering studies on dissolved and solid glue and provide microscopy images of glue surfaces and sections, revealing a porous interior that is consistent with the high water content (85-90 wt %) of moist glue. In addition to compositional similarities with other biological adhesives and well-known elastomeric proteins, the circular dichroism spectrum of dissolved glue is almost identical to that for soluble elastin and electron and scanning probe microscopy images invite comparison with silk fibroins. Covalent cross-linking does not seem to be necessary for the glue to set.

The X-ray structure of a hemipteran ecdysone receptor ligand-binding domain: comparison with a lepidopteran ecdysone receptor ligand-binding domain and implications for insecticide design

The ecdysone receptor is a hormone-dependent transcription factor that plays a central role in regulating the expression of vast networks of genes during development and reproduction in the phylum Arthropoda. The functional receptor is a heterodimer of the two nuclear receptor proteins ecdysone receptor (EcR) and ultraspiracle protein. The receptor is the target of the environmentally friendly bisacylhydrazine insecticides, which are effective against Lepidoptera but not against Hemiptera or several other insect orders. Here we present evidence indicating that much of the selectivity of the bisacylhydrazine insecticides can be studied at the level of their binding to purified ecdysone receptor ligand-binding domain (LBD) heterodimers. We report the crystal structure of the ecdysone receptor LBD heterodimer of the hemipteran Bemisia tabaci (Bt, sweet potato whitefly) in complex with the ecdysone analogue ponasterone A. Although comparison with the corresponding known LBD structure from the lepidopteran Heliothis virescens (Hv) ecdysone receptor revealed the overall mode of ponasterone A binding to be very similar in the two cases, we observed that the BtEcR ecdysteroid-binding pocket is structured differently to that of HvEcR in those parts that are not in contact with ponasterone A. We suggest that these differences in the ligand-binding pocket may provide a molecular basis for the taxonomic order selectivity of bisacylhydrazine insecticides.

Isolating substrates for an engineered alpha-lytic protease by phage display

Panning of a substrate phage library with an alpha-lytic protease mutant showed that substrate phage display can be used to isolate sequences with improved protease sensitivity even for proteases of relatively broad specificity. Two panning experiments were performed with an engineered alpha-lytic protease mutant known to have a preference for cleavage after His or Met residues. Both experiments led to the isolation of protease-sensitive phage containing linker sequences in which His and Met residues were enriched compared with the initial library. Despite the relatively hydrophobic substrate binding site of the enzyme, the predominant protease-sensitive sequence isolated from the second library panning had the sequence Asp-Ser-Thr-Met. Kinetic studies showed that this sequence was cleaved up to 4.5-fold faster than rationally designed positive controls. Protease-resistant phage particles were also selected and characterized, with the finding that Gly and Pro appeared frequently at the putative P4 positions, whereas Asp dominated the putative P1 position.

Role of insulin-like growth factor binding protein-3 in breast cancer cell growth

The mitogenic effects of insulin-like growth factors (IGFs) are regulated by a family of insulin-like growth factor binding proteins (IGFBPs). One member of this family, IGFBP-3, mediates the growth-inhibitory and apoptosis-inducing effects of a number of growth factors and hormones such as transforming growth factor-beta, retinoic acid, and 1,25-dihydroxyvitamin D3. IGFBP-3 may act in an IGF-dependent manner by attenuating the interaction of pericellular IGFs with the type-I IGF receptor. It may also act in an IGF-independent manner by initiating intracellular signaling from a cell surface receptor, or by direct nuclear action, or both. The possibility of a membrane-bound receptor is strengthened by recent studies which have identified members of the transforming growth factor-beta receptor family as having a role, either directly or indirectly, in signaling from the cell surface by IGFBP-3. A number of growth factors and hormones stimulate the expression and secretion of cellular IGFBP-3, which then signals from the cell surface to bring about some of the effects attributed to the primary agents. Within the cell, the apoptosis-inducing tumor suppressor, p53, can also induce IGFBP-3 expression and secretion. Since IGFBP-3 upregulates the cell cycle inhibitor, p21(Waf1), and increases the ratio of proapoptotic to antiapoptotic members of the Bcl family, it appears to exert the same effects on major downstream targets of cell signaling as p53 does. The nuclear localization of IGFBP-3 has been described in a number of cell types. IGFBP-3 may act to import IGFs or other nuclear localization signal-deficient signaling molecules into the nucleus. It may also act directly in the nucleus by enhancing the activity of retinoid X receptor-alpha and thereby promote apoptosis. All of the above phenomena will be discussed with particular emphasis on the growth of breast cancer cells.

Ecdysone-controlled expression of transgenes

Inducible expression systems show great potential for use in human gene therapy and systems based on insect ecdysone receptors are particularly promising candidates. This article describes such systems and reviews actual and potential uses of ecdysone-controlled transgenes in vitro and in vivo. The ligand specificity of ecdysone receptor-based systems is considered, along with the safety and efficacy of the ecdysteroid and non-steroidal compounds used to activate them.

Linkers for improved cleavage of fusion proteins with an engineered alpha-lytic protease

Addition of an N-terminal fusion partner can greatly aid the expression and purification of a recombinant protein in Escherichia coli. We investigated two genetically engineered proteases designed to remove the fusion partner after the protein of interest has been expressed. Recombinant human insulin-like growth factor-II (hIGF-II) has been produced from E. coli-derived fusion proteins using a novel enzymatic cleavage system that uses a mutant of alpha-lytic protease. Initially, two potential fusion protein linkers were designed, Pro-Ala-Pro-His (PAPH) and Pro-Ala-Pro-Met (PAPM), and were tested as substrates in the form of synthetic dodecapeptides. Using mass spectrometry and reverse-phase HPLC, the position of cleavage was confirmed and the kinetics of synthetic peptide cleavage were examined. Use of the linkers in hIGF-II fusion proteins produced in E. coli was then evaluated. The fusion proteins constructed consist of the first 11 amino acids of porcine growth hormone linked N-terminally to hIGF-II by six amino acids that include the dipeptide Val-Asn followed by a variable tetrapeptide protease cleavage motif. Mass spectrometry and N-terminal sequencing confirmed that proteolytic cleavage of the fusion proteins had occurred at the predicted sites. Using the fusion proteins as substrates, the cleavage of the rationally designed motifs by the alpha-lytic protease mutant was compared. The fusion protein containing the motif PAPM had a k(cat)/K(M) ratio indicating a 1.6-fold preference over the PAPH fusion protein for cleavage by this enzyme. Furthermore, when hIGF-II fusion proteins containing the designed cleavable linkers were processed with the engineered alpha-lytic protease, they gave greatly improved yields of native hIGF-II compared to an analogous fusion protein cleaved by H64A subtilisin. Comparison of the peptide and protein cleavage studies shows that the efficient proteolysis of the cleavage motifs is an inherent property of the designed sequences and is not determined by secondary or tertiary structure in the fusion proteins.

Human perlecan immunopurified from different endothelial cell sources has different adhesive properties for vascular cells

Perlecan, a major heparan sulfate proteoglycan of vascularized tissues, was immunopurified from media conditioned by human endothelial cells of both arterial and venous origin. The heparan sulfate moiety of perlecan from cultured arterial cells differed in amount and/or composition from that produced by a transformed cell line of venous origin. Both forms of perlecan bound basic fibroblast growth factor with Kd approximately 70 nM. In ELISA experiments, perlecan and its protein core bound to various extracellular matrix components in a manner that was strongly influenced by the format of the assay. Human vascular smooth muscle cells and human endothelial cells adhered to perlecan-coated surfaces, and both cell types adhered better to the venous cell-derived than to the arterial cell-derived perlecan. Removal of the heparan sulfate chains abolished this difference and increased the ability of both types of perlecan to adhere vascular cells. Denaturation of perlecan and its protein core also rendered each of them more adhesive, indicating the presence of conformation-independent adhesion determinants in the polypeptide sequence. Their location was investigated using recombinant perlecan domains. Overall, our results represent the first demonstration of human perlecan acting as an adhesive molecule for human vascular cells and suggest that it may play a role in vascular wound healing.

Combinatorial strategies for the discovery of novel protease specificities

This article discusses proven and possible ways to generate novel cleavage specificities in serine proteases using combinatorial mutagenesis, compares the different ways of screening or selecting for desirable mutants, and examines the ways in which combinatorial substrate libraries can be used to gain a more comprehensive insight into protease cleavage preferences. The use of bacteriophage to display both combinatorial protease libraries and combinatorial substrate libraries will be discussed.

Expression of human perlecan domain I as a recombinant heparan sulfate proteoglycan with 20-kDa glycosaminoglycan chains

Recombinant forms of human perlecan domain I were secreted as proteoglycans by stably transfected human 293 cells. A recombinant domain I-only proteoglycan spanned the 95- to 265-kDa region in SDS-PAGE and appeared to be 160 kDa in denaturing gel filtration. Its glycosaminoglycan (GAG) content was approximately 67% heparan sulfate, and its average GAG chain size of 20 kDa suggested that the true molecular mass of the proteoglycan was 90 kDa. Domain I with enhanced green fluorescent protein fused to its C-terminus had an apparent molecular mass of 210-220 kDa and contained approximately 100% heparan sulfate. Its average GAG chain size (also 20 kDa) suggested a true molecular mass of 117 kDa for this proteoglycan. Its sulfate content of 53-77 mol SO2-4 per mole of protein indicated the presence of one sulfate group per 4-7 GAG sugar residues.

Cloning of a Lysobacter enzymogenes gene that encodes an arginyl endopeptidase (endoproteinase Arg-C)

Screening an expression library of Lysobacter enzymogenes DNA allowed us to clone a gene encoding a serine protease that cleaves synthetic substrates C-terminal to Arg and, to a lesser extent, Lys residues. The gene product, which shares sequence homology with the lysyl endopeptidases from L. enzymogenes and Achromobacter lyticus, consists of a signal sequence (24 residues), pro-region ( approximately 195 residues), and catalytic domain ( approximately 244 residues). Downstream of this gene is an open reading frame that lacks a promoter and appears to encode an inactive type I subtilase.

Inhibition of phenotype modulation, growth, and migration of vascular smooth muscle cells by a guanosine-rich 30-mer phosphorothioate oligodeoxynucleotide

The testing of a 30-mer dG-rich phosphorothioate oligodeoxynucleotide (LG4PS) for effects on the behaviour of vascular smooth muscle cells (VSMC) in vitro and in vivo is described. LG4PS at 0.3 microM inhibited significantly the phenotype modulation of freshly isolated rabbit VSMC, and cell outgrowth from pig aortic explants was inhibited approximately 80% by 5 microM LG4PS. The growth of proliferating rabbit and pig VSMC was inhibited approximately 70% by 0.3 microM and 5 microM LG4PS, respectively. Though less marked, the antiproliferative effects of LG4PS on human VSMC were comparable to those obtained with heparin. The cytotoxic effects of LG4PS on VSMC in vitro were low. Despite these promising results, adventitial application of 2-200 nmol LG4PS in pluronic gel failed to reduce vascular hyperplasia in balloon-injured rabbit carotid arteries, and the highest dose caused extensive mortality.

Comparison of the heparanase enzymes from mouse melanoma cells, mouse macrophages, and human platelets

The intracellular heparanases from mouse macrophage and melanoma cells are very similar in terms of their size (60-80 kDa), pI (5.3-4.1), pH optimum (< or = 5.5), and interactions with heparin. These proteins are therefore likely to be identical, suggesting that tumour and blood cells utilise the same heparanase enzyme. The human platelet enzyme is similar to the mouse enzymes in terms of pH optimum (< or = 5.5) and pI value (5.3-4.8), but appears to be smaller in size (40-60 kDa). It also seems to differ from the mouse enzymes in aspects of its surface charge, and in its interactions with heparin. There was no indication that proteolysis was of significance for the enzymes, nor that they contained any sialic acid residues.

Activation of platelet heparitinase by vascular cell lysates

Tumour cells have been reported to contain an activator of platelet heparitinase which is absent from normal cells. Using an assay which measures the degradation of radiolabelled heparin, we observed that lysates of metastatic melanoma cells did activate platelet radiolabelled heparin, we observed that lysates of metastatic melanoma cells did activate platelet heparitinase but that lysates of arterial endothelial and smooth muscle cells did likewise, with the latter being particularly effective. The activator largely survived a 10 min preincubation of the cell lysates at 70 degrees C, but not at 100 degrees C. Experimental results indicated that the contents of 10(5) vascular smooth muscle cells could increase platelet heparitinase activity in vitro to 6 times its initial value. We suggest such activation may have physiological relevance and may even assist the development of certain cardiovascular diseases in man.

Inhibition of platelet heparitinase by phosphorothioate DNA oligonucleotides

In view of the role that heparitinase and heparanase enzymes are thought to play in regulating the proliferation of smooth muscle cells, inhibitors of these enzymes may have therapeutic value in the treatment of vascular hyperplasia. Here we report that phosphorothioate oligodeoxynucleotides inhibit platelet heparitinase and related enzymes in vitro. The inhibition is greatly enhanced by the presence of a GGG motif in the oligonucleotide, and also increases with oligonucleotide for two phosphorothioate DNA 30-mers consisting solely of guanosine and thymidine nucleotides. Their inhibitory efficacy was greater when heparan sulphate was used as substrate.

Metastatic papillary thyroid carcinoma presenting as a primary renal neoplasm

Clinically detectable thyroid cancer metastatic to the kidney is rare, with only six cases reported in the medical literature. Four of these have been follicular carcinoma, one papillary carcinoma, and one described as a thyroid adenoma. All of these had known thyroid neoplasms prior to development of their renal metastases. We report herein a seventh case of thyroid carcinoma metastatic to the kidney, unique in that the diagnosis of the kidney metastasis preceded the knowledge of the primary thyroid neoplasm. Furthermore, the follicular variant of papillary cancer, present in this case, has not been previously described in renal metastases from thyroid cancer. Treatment of the kidney metastases led to the subsequent discovery and treatment of the primary thyroid cancer. The patient underwent nephrectomy followed by total thyroidectomy, and is alive and disease-free 3 years postoperatively. Thyroid cancer metastatic to the kidney is rare clinically, but can be amenable to treatment with good long term results.

Purification and characterization of S1 mutants of alpha-lytic protease having altered catalytic properties

A procedure is described for purifying alpha-lytic protease and its mutants from culture supernatants of recombinant Escherichia coli. The method affords substantial amounts (approx. 80 mg) of homogeneous enzyme. We compared the cleavage preferences of wild-type alpha-lytic protease and of mutants containing the substitutions Ala190 ("parent"), Ala190/Val192/His213/Met218 (mutant 1), Ala190/His213/Leu218 (mutant 9), and Ala190/Thr213/Leu218 (mutant 55), and for each enzyme we found broad agreement between the results obtained with synthetic ester and amide substrates. Kinetic constants were determined for the purified enzymes using selected tetrapeptide p-nitroanilide substrates. Mutant 55 had broad specificity and high activity. In terms of kcat/Km it cleaved at Met and Phe residues two to three times as effectively as the Ala190 enzyme and cleaved at Ala 7 times more effectively than the wild-type protease. The Ala190/His213 enzymes showed a preference for cleavage at His and Met residues. Not only were their kcat values for cleavage at His increased (in relation to the Ala190 enzyme) by an order of magnitude, but they also exhibited large decreases in kcat/Km for cleavage at other residues; for example, the value for cleavage at Phe was 400- to 600-fold lower. Mutant 9 cleaved a recombinant IGF-II fusion protein at a unique His residue and also at a nearby Asn residue.

Cost-effectiveness of preoperative localization studies in primary hyperparathyroid disease

OBJECTIVE

To evaluate the effect of preoperative localization studies on the surgical management of patients with primary hyperparathyroid disease (PHPT).

SUMMARY BACKGROUND DATA

Reported cure rates of initial surgical exploration for PHPT are close to 95%. Preoperative localization studies are frequently obtained to improve surgical success and decrease operative time.

METHODS

Initial cervical exploration was performed in 113 patients with PHPT from 1981 to 1993. Twenty-four patients (21%) had surgery without preoperative localization studies. The remaining 89 patients (79%) had 132 noninvasive preoperative localization studies. Success of the localization studies in tumor localization, pathologic findings, postoperative serum calcium levels, and operative times were compared. Patient costs of the studies were calculated.

RESULTS

Disease was identified during operation in 23 of 24 patients (96%) having cervical exploration without preoperative localization studies, and they had normal calcium levels after surgery. Eighty-seven of 89 patients (98%) having preoperative localization studies were surgically cured. The highest sensitivity rate (60%) and highest positive predictive value (79%) of the localization studies were found with thallium-technetium scintiscanning. Average cost of the localization studies was $901 per patient. Combination studies were obtained in 32 patients at an average cost of $1,314 per patient without improving sensitivity. Mean operating time did not differ for localized and nonlocalized patients.

CONCLUSIONS

Preoperative localization studies did not improve parathyroid localization or cure rate and did not substantially shorten operating time in initial cervical exploration for PHPT. The economic burden of routine preoperative localization studies in these patients is not justified.

A new library of alpha-lytic protease S1 mutants generated by combinatorial random substitution

Four positions in the S1 site of alpha-lytic protease (positions 190, 192, 213 and 218) were subjected to targeted random mutagenesis. In the resulting library we found active mutant proteases whose cleavage preferences could be grouped into three distinct families. Some potentially useful enzymes (such as one that prefers to cleave at Asn and Cys residues) were identified. In addition, we discuss instances where it was possible to relate changes in substrate specificity to alterations in the structure of the substrate binding site.

Calciphylaxis: early recognition and management

Calciphylaxis, a syndrome of disseminated calcification found in chronic renal failure patients with secondary hyperparathyroidism, results in soft tissue calcification and vascular medial calcinosis leading to subsequent ischemic tissue necrosis. It is a rarely occurring condition in which patients present with painful, violaceous, mottled lesions of the extremities and/or trunk that progress to skin and subcutaneous tissue necrosis, non-healing ulcers, and gangrene. We reviewed the clinical course of seven patients (aged 24-69) with calciphylaxis treated at our institution over a 4-year period (October 1988-June 1992). All seven patients underwent parathyroidectomy, with a mean time of 8 weeks (range 3-20 weeks) between the onset of calciphylactic symptoms and parathyroidectomy. Four patients died, three secondary to wound-related sepsis. Of the three survivors, two healed soft tissue lesions primarily. The other required extremity amputation and wound excision before healing. Neither anatomical location of the soft tissue lesions nor post-parathyroidectomy serum calcium and phosphorus levels had any bearing on wound healing or mortality. Lesion severity at the time of parathyroidectomy appeared to best correlate with clinical course. Although treatment with phosphate-binding antacids, total or subtotal parathyroidectomy, and avoidance of challengers such as Vitamin D or local tissue trauma remain the mainstays of therapy, the uniform cure for calciphylaxis remains elusive. Prognosis for patients with calciphylaxis is dismal, even following late surgical intervention. Earlier recognition of the signs and symptoms of calciphylaxis should lead to timely parathyroidectomy in the hopes of ameliorating the symptoms and preventing or retarding its progressive sequelae.

Laparoscopic cholecystectomy in biliary pancreatitis

Laparoscopic cholecystectomy has emerged as the treatment of choice for uncomplicated cholelithiasis. Despite early concerns, many surgeons have applied this new technique to more complicated biliary tract disease states, including biliary pancreatitis. To evaluate the safety of laparoscopic cholecystectomy in this setting, we retrospectively reviewed 29 patients with clinical and laboratory evidence of biliary pancreatitis who underwent this procedure between March 1990 and December 1992. The severity of pancreatitis was determined by Ranson's criteria. Two patients had a Ranson's score of 6, one of 5, one of 4, five scored 3, nine scored 2, nine also scored 1, and two patients scored 0. The mean serum amylase level on admission was 1,610 (range 148 to 7680). All patients underwent laparoscopic cholecystectomy during the same hospital admission for biliary pancreatitis, with the mean time of operation being 5.5 days from admission. Operative time averaged 123 minutes (range 60-220 minutes). Intraoperative cholangiography was obtained in 76 per cent of patients. Three patients had choledocholithiasis on intraoperative cholangiography and were treated with choledochoscopy, laparoscopic common bile duct exploration, and saline flushing of the duct. The mean length of hospital stay was 11 days (range 5-32 days). There were seven postoperative complications requiring prolonged hospitalization with all but one treated non-operatively. One patient with a preoperative Ranson score of 6 developed necrotizing pancreatitis and subsequently required operative pancreatic debridement and drainage. There were no deaths in this series and no postoperative wound infections. The average recovery period for return to work was 2 weeks. These statistics compare favorably with literature reports for open cholecystectomy in biliary pancreatitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Over-expression of the yeast multifunctional arom protein

The pentafunctional arom protein of Saccharomyces cerevisiae is encoded by the ARO1 gene. Substantial elevation of the levels of the arom protein (25-fold) was achieved in yeast using a vector that exploited the ubiquitin-fusion cleavage system of yeast. However, attempts to express the N-terminal 3-dehydroquinate synthase domain (E1) or the internal 3-dehydroquinase domain (E2) using the same system did not succeed. The yeast arom protein was successfully purified from the over-expressing transformant, and was found to possess all five enzymatic activities in a ratio similar to that observed in crude cell extracts. The purified material consisted mainly of a polypeptide that co-migrated in SDS-PAGE with intact arom proteins from other species.

Random mutagenesis of the substrate-binding site of a serine protease can generate enzymes with increased activities and altered primary specificities

In the past, several point mutations have been introduced individually into the substrate-binding site of alpha-lytic protease (EC 3.4.21.12) and shown to affect its specificity in a predictable manner [Bone, R., Silen, J. L., & Agard, D. A. (1989) Nature 339, 191-195]. One of the resulting mutant enzymes (Met190Ala in the numbering system of Fujinaga et al.) [Fujinaga, M., Delbaere, L. T. J., Brayer, G. D., & James, M. N. G. (1985) J. Mol. Biol. 183, 479-502] cleaves at large hydrophobic residues. We chose this enzyme as the parent for a library of mutant proteases. The library was constructed by effecting combinatorial random substitution of up to four other residues (Gly191, Arg192, Met213, and Val218) thought likely to influence the primary specificity of the protease. Active enzymes in the library were screened with a range of synthetic substrates (encompassing 19 different amino acids in the P1 position) in order to evaluate their primary cleavage preferences. The amino acid sequences of active mutants revealed a strong preference for the replacement of Met213 with a His residue. This substitution also had the greatest observed effect on specificity, conferring a greatly increased and, in some cases, dominant ability to cleave at His residues in synthetic amide substrates. Mutant enzymes with greatly increased proteolytic activity were also found in the library.

Safety, efficacy, cost, and morbidity of laparoscopic versus open cholecystectomy: a prospective analysis of 228 consecutive patients

Laparoscopic cholecystectomy has become the procedure of choice in most hospitals for the resolution of surgically treatable gallbladder disease. Few reports address the results of laparoscopic cholecystectomy in comparison to open cholecystectomy during the same time interval within the same institution. One hundred ninety-six laparoscopic cholecystectomies were performed from April 1990 through February 1991. Initial patient selection was restricted to elective procedures for chronic cholecystitis with expanded indications as experience was gained. Of the 196 cases, 11 required conversion to open cholecystectomy, leaving 185 laparoscopic cholecystectomies for comparison. During the same period, 82 open cholecystectomies were performed. Thirty-nine of these were complicated cases and would not have been considered for laparoscopic cholecystectomy early in the study, leaving 43 routine open cholecystectomies for comparative purposes. In the laparoscopic group, 1.1 per cent of the patients had major operative complications as opposed to the open group, which had none. There were no common bile duct injuries in either group. To provide a true cost-benefit analysis, a group of patients was identified that would qualify for elective, same-day admission for either an open or laparoscopic procedure. Laparoscopic cholecystectomy (LC) was performed on 70 patients, and open cholecystectomy (OC) was performed on 26 patients. A comparison of data from these groups showed no significant difference in age or sex. Hospitalization costs averaged $5,390 for the LC group versus $5,392 for the OC group. Postoperative hospital stay averaged 1.3 days for the LC group versus 3.7 days for the OC group (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Morbidity associated with long-term methotrexate therapy in juvenile rheumatoid arthritis

To evaluate the adverse effects associated with long-term methotrexate (MTX) therapy in children with juvenile rheumatoid arthritis, we conducted a retrospective review of 62 patients with polyarticular juvenile rheumatoid arthritis, treated from 84 to 296 weeks with MTX weekly. Pulmonary function testing was performed before MTX therapy on 46 patients older than 6 years of age; 26 patients had serial pulmonary function testing, and no abnormalities were detected. In all 62 patients, liver function (alanine aminotransferase and aspartate aminotransferase activity) was monitored every 3 months. Transient liver function abnormalities developed in nine patients during treatment. Twelve patients underwent percutaneous liver biopsies after receiving 815 to 2980 mg of MTX; none had fibrosis or cirrhosis. Macrocytic anemia developed in one child receiving simultaneous long-term trimethoprim-sulfamethoxazole therapy and resolved after the trimethoprim-sulfamethoxazole was discontinued. No stomatitis or rashes were observed. Six patients were able to discontinue MTX therapy when their disease remitted; 56 continue MTX therapy. No child permanently discontinued MTX therapy because of an adverse effect. These data suggest that MTX may be better tolerated in children with juvenile rheumatoid arthritis than in adults with rheumatoid arthritis.

Identification of the active-site lysine residues of two biosynthetic 3-dehydroquinases

The lysine residues involved in Schiff-base formation at the active sites of both the 3-dehydroquinase component of the pentafunctional arom enzyme of Neurospora crassa and of the monofunctional 3-dehydroquinase of Escherichia coli were labelled by treatment with 3-dehydroquinate in the presence of NaB3H4. Radioactive peptides were isolated by h.p.l.c. following digestion with CNBr (and in one case after further digestion with trypsin). The sequence established for the N. crassa peptide was ALQHGDVVKLVVGAR, and that for the E. coli peptide was QSFDADIPKIA. An amended nucleotide sequence for the E. coli gene (aroD) that encode 3-dehydroquinase is also presented, along with a revised alignment of the deduced amino acid sequences for the biosynthetic enzymes.

Interactions of lipoyl domains with the E1p subunits of the pyruvate dehydrogenase multienzyme complex from Escherichia coli

Equilibrium binding experiments were carried out with lipoyl domains and the pyruvate decarboxylase [pyruvate dehydrogenase (lipoamide), E1p, EC 1.2.4.1)] component of the pyruvate dehydrogenase multienzyme complex of Escherichia coli. The dissociation constant (Ks) was estimated to be not less than 0.3 mM, exceeding the Km value (33 microM) for reductive acetylation of the domains by an order of magnitude. Thus, the lipoyl domain, which is required to promote reductive acetylation of the lipoyl group, does not appear to do this simply by enhancing the binding to E1p. The difference between Ks and Km suggests that the formation and release of reductively acetylated lipoyl domains from the enzyme may be a relatively rapid step in the mechanism.