Using BpyAla to generate copper artificial metalloenzymes: a catalytic and structural study

Artificial metalloenzymes (ArMs) have emerged as a promising avenue in the field of biocatalysis, offering new reactivity. However, their design remains challenging due to the limited understanding of their protein dynamics and how the introduced cofactors alter the protein scaffold structure. Here we present the structures and catalytic activity of novel copper ArMs capable of (R)- or (S)-stereoselective control, utilizing a steroid carrier protein (SCP) scaffold. To incorporate 2,2'-bipyridine (Bpy) into SCP, two distinct strategies were employed: either Bpy was introduced as an unnatural amino acid (2,2'-bipyridin-5-yl)alanine (BpyAla) using amber stop codon expression or via bioconjugation of bromomethyl-Bpy to cysteine residues. The resulting ArMs proved to be effective at catalysing an enantioselective Friedel-Crafts reaction with SCP_Q111BpyAla achieving the best selectivity with an enantioselectivity of 72% ee (S). Interestingly, despite using the same protein scaffold, different attachment strategies for Bpy at the same residue (Q111) led to a switch in the enantiopreference of the ArM. X-ray crystal structures of SCP_Q111CBpy and SCP_Q111BpyAla ArMs with bound Cu(ii) ions unveiled crucial differences in the orientation of the catalytic centre. Combining structural information, alanine scanning studies, and computational analysis shed light on the distinct active sites of the ArMs, clarifying that these active sites stabilise the nucleophilic substrate on different sides of the electrophile leading to the observed switch in enantioselectivity. This work underscores the importance of integrating structural studies with catalytic screening to unravel the intricacies of ArM behaviour and facilitate their development for targeted applications in biocatalysis.

Fluorescence-resonance-energy-transfer-based assay to estimate modulation of TDP1 activity through arginine methylation

Tyrosyl DNA phosphodiesterase (TDP1) is a DNA repair enzyme that hydrolyzes the phosphotyrosyl linkage between 3'-DNA-protein crosslinks such as stalled topoisomerase 1 cleavage complexes (Top1cc). Here, we present a fluorescence-resonance-energy-transfer-(FRET) based assay to estimate modulation of TDP1 activity through arginine methylation. We describe steps for TDP1 expression and purification and estimating TDP1 activity using fluorescence-quenched probes mimicking Top1cc. We then detail data analysis of real-time TDP1 activity and screening of TDP1-selective inhibitors. For complete details on the use and execution of this protocol, please refer to Bhattacharjee et al. (2022).¹.

Interplay between symmetric arginine dimethylation and ubiquitylation regulates TDP1 proteostasis for the repair of topoisomerase I-DNA adducts

Tyrosyl-DNA phosphodiesterase (TDP1) hydrolyzes the phosphodiester bond between a DNA 3' end and a tyrosyl moiety and is implicated in the repair of trapped topoisomerase I (Top1)-DNA covalent complexes (Top1cc). Protein arginine methyltransferase 5 (PRMT5) catalyzes arginine methylation of TDP1 at the residues R361 and R586. Here, we establish mechanistic crosstalk between TDP1 arginine methylation and ubiquitylation, which is critical for TDP1 homeostasis and cellular responses to Top1 poisons. We show that R586 methylation promotes TDP1 ubiquitylation, which facilitates ubiquitin/proteasome-dependent TDP1 turnover by impeding the binding of UCHL3 (deubiquitylase enzyme) with TDP1. TDP1-R586 also promotes TDP1-XRCC1 binding and XRCC1 foci formation at Top1cc-damage sites. Intriguingly, R361 methylation enhances the 3'-phosphodiesterase activity of TDP1 in real-time fluorescence-based cleavage assays, and this was rationalized using structural modeling. Together, our findings establish arginine methylation as a co-regulator of TDP1 proteostasis and activity, which modulates the repair of trapped Top1cc.

Phosphorylation of NANOG by casein kinase I regulates embryonic stem cell self-renewal

The self-renewal efficiency of mouse embryonic stem cells (ESCs) is determined by the concentration of the transcription factor NANOG. While NANOG binds thousands of sites in chromatin, the regulatory systems that control DNA binding are poorly characterised. Here, we show that NANOG is phosphorylated by casein kinase I, and identify target residues. Phosphomimetic substitutions at phosphorylation sites within the homeodomain (S130 and S131) have site-specific functional effects. Phosphomimetic substitution of S130 abolishes DNA binding by NANOG and eliminates LIF-independent self-renewal. In contrast, phosphomimetic substitution of S131 enhances LIF-independent self-renewal, without influencing DNA binding. Modelling the DNA-homeodomain complex explains the disparate effects of these phosphomimetic substitutions. These results indicate how phosphorylation may influence NANOG homeodomain interactions that underpin ESC self-renewal.

Structural basis for DNA 3'-end processing by human tyrosyl-DNA phosphodiesterase 1

Tyrosyl-DNA phosphodiesterase (Tdp1) is a DNA 3'-end processing enzyme that repairs topoisomerase 1B-induced DNA damage. We use a new tool combining site-specific DNA-protein cross-linking with mass spectrometry to identify Tdp1 interactions with DNA. A conserved phenylalanine (F259) of Tdp1, required for efficient DNA processing in biochemical assays, cross-links to defined positions in DNA substrates. Crystal structures of Tdp1-DNA complexes capture the DNA repair machinery after 3'-end cleavage; these reveal how Tdp1 coordinates the 3'-phosphorylated product of nucleosidase activity and accommodates duplex DNA. A hydrophobic wedge splits the DNA ends, directing the scissile strand through a channel towards the active site. The F259 side-chain stacks against the -3 base pair, delimiting the junction of duplexed and melted DNA, and fixes the scissile strand in the channel. Our results explain why Tdp1 cleavage is non-processive and provide a molecular basis for DNA 3'-end processing by Tdp1.

Use of mariner transposases for one-step delivery and integration of DNA in prokaryotes and eukaryotes by transfection

Delivery of DNA to cells and its subsequent integration into the host genome is a fundamental task in molecular biology, biotechnology and gene therapy. Here we describe an IP-free one-step method that enables stable genome integration into either prokaryotic or eukaryotic cells. A synthetic mariner transposon is generated by flanking a DNA sequence with short inverted repeats. When purified recombinant Mos1 or Mboumar-9 transposase is co-transfected with transposon-containing plasmid DNA, it penetrates prokaryotic or eukaryotic cells and integrates the target DNA into the genome. In vivo integrations by purified transposase can be achieved by electroporation, chemical transfection or Lipofection of the transposase:DNA mixture, in contrast to other published transposon-based protocols which require electroporation or microinjection. As in other transposome systems, no helper plasmids are required since transposases are not expressed inside the host cells, thus leading to generation of stable cell lines. Since it does not require electroporation or microinjection, this tool has the potential to be applied for automated high-throughput creation of libraries of random integrants for purposes including gene knock-out libraries, screening for optimal integration positions or safe genome locations in different organisms, selection of the highest production of valuable compounds for biotechnology, and sequencing.

Development of a Continuous Fluorescence Assay for Rhinovirus 14 3C Protease Using Synthetic Peptides

Rhinovirus 3C protease is an attractive target for therapeutic intervention owing to its important role in virion maturation and infectivity. In order to facilitate the identification of potential 3C protease inhibitors, we have developed a continuous fluorescence assay using 5-[(2-aminoethyl)amino]naphthalene-1-sulphonic acid (Edans) as a fluorescent donor and 4-(4-dimethylaminophenylazo)benzoic acid (Dabcyl) as a quenching acceptor. Several fluorogenic peptide substrates for 3C protease were synthesized by both solution chemistry and solid phase peptide synthesis. One of the synthetic Edans/Dabcyl substrates, with an amino acid sequence derived from the 2C/3A site of the virus polyprotein, yielded a 24-fold increase in fluorescence intensity after 3C cleavage. Data regarding substrate cleavage kinetics, assay sensitivity and optimization are presented. The application of this assay to the evaluation of 3C protease inhibitors is also shown.

A bend, flip and trap mechanism for transposon integration

Cut-and-paste DNA transposons of the mariner/Tc1 family are useful tools for genome engineering and are inserted specifically at TA target sites. A crystal structure of the mariner transposase Mos1 (derived from Drosophila mauritiana), in complex with transposon ends covalently joined to target DNA, portrays the transposition machinery after DNA integration. It reveals severe distortion of target DNA and flipping of the target adenines into extra-helical positions. Fluorescence experiments confirm dynamic base flipping in solution. Transposase residues W159, R186, F187 and K190 stabilise the target DNA distortions and are required for efficient transposon integration and transposition in vitro. Transposase recognises the flipped target adenines via base-specific interactions with backbone atoms, offering a molecular basis for TA target sequence selection. Our results will provide a template for re-designing mariner/Tc1 transposases with modified target specificities.

DOI:http://dx.doi.org/10.7554/eLife.15537.001

The complete set of DNA in a cell is referred to as its genome. Most genomes contain short fragments of DNA called transposons that can jump from one place to another. Transposons carry sections of DNA with them when they move, which creates diversity and can influence the evolution of a species. Transposons are also being exploited to develop tools for biotechnology and medical applications. One family of transposons – the Mariner/Tc1 family – has proved particularly useful in these endeavours because it is widespread in nature and can jump around the genomes of a broad range of species, including mammals.

DNA transposons are cut out of their position and then pasted at a new site by an enzyme called transposase, which is encoded by some of the DNA within the transposon. DNA is made up of strings of molecules called bases and Mariner/Tc1-family transposons can only insert into a new position in the genome at sites that have a specific sequence of two bases. However, it was not known how this target sequence is chosen and how the transposon inserts into it.

Morris et al. have now used a technique called X-ray crystallography to build a three-dimensional model of a Mariner/Tc1-family transposon as it inserts into a new position. The model shows that, as the transposon is pasted into its new site, the surrounding DNA bends. This causes two DNA bases in the surrounding DNA to flip out from their normal position in the DNA molecule, which enables them to be recognised by the transposase. Further experiments showed that this base-flipping is dynamic, that is, the two bases continuously flip in and out of position. Furthermore, Morris et al. identified which parts of the transposase enzyme are required for the transposon to be efficiently pasted into the genome.

Together these findings may help researchers to alter the transposase so that it can insert the transposon into different locations in a genome. This will hopefully lead to new tools for biotechnology and medical applications.

DOI:http://dx.doi.org/10.7554/eLife.15537.002

Physico-chemical confinement of helical nanofilaments

Helical nanofilaments (HNFs) have attracted much interest because of their unique optical properties, but there have been many hurdles to overcome in using them for the practical applications due to their structural complexity. Here we demonstrate that the molecular configuration and layer conformation of a modulated HNF (HNFs(mod)) can be studied using a physicochemical confinement system. The layer directions affected by the chemical affinity between the mesogen and surface were drastically controlled in surface-modified nanochannels. Furthermore, an in situ experiment using grazing-incidence X-ray diffraction (GIXD) was carried out to investigate in detail the structural evolution through thermal transitions. The results demonstrate that the HNF(mod) structure can be perfectly controlled for functional HNF device applications, and a combined system with chemical and physical confinement effects will be helpful to better understand the fundamentals of soft matter.

Structural Basis for the Inverted Repeat Preferences of mariner Transposases

The inverted repeat (IR) sequences delimiting the left and right ends of many naturally active mariner DNA transposons are non-identical and have different affinities for their transposase. We have compared the preferences of two active mariner transposases, Mos1 and Mboumar-9, for their imperfect transposon IRs in each step of transposition: DNA binding, DNA cleavage, and DNA strand transfer. A 3.1 Å resolution crystal structure of the Mos1 paired-end complex containing the pre-cleaved left IR sequences reveals the molecular basis for the reduced affinity of the Mos1 transposase DNA-binding domain for the left IR as compared with the right IR. For both Mos1 and Mboumar-9, in vitro DNA transposition is most efficient when the preferred IR sequence is present at both transposon ends. We find that this is due to the higher efficiency of cleavage and strand transfer of the preferred transposon end. We show that the efficiency of Mboumar-9 transposition is improved almost 4-fold by changing the 3′ base of the preferred Mboumar-9 IR from guanine to adenine. This preference for adenine at the reactive 3′ end for both Mos1 and Mboumar-9 may be a general feature of mariner transposition.

Structural role of the flanking DNA in mariner transposon excision

During cut-and-paste mariner/Tc1 transposition, transposon DNA is cut precisely at its junction with flanking DNA, ensuring the transposon is neither shortened nor lengthened with each transposition event. Each transposon end is flanked by a TpA dinucleotide: the signature target site duplication of mariner/Tc1 transposition. To establish the role of this sequence in accurate DNA cleavage, we have determined the crystal structure of a pre-second strand cleavage mariner Mos1 transpososome. The structure reveals the route of an intact DNA strand through the transposase active site before second strand cleavage. The crossed architecture of this pre-second strand cleavage paired-end complex supports our proposal that second strand cleavage occurs in trans. The conserved mariner transposase WVPHEL and YSPDL motifs position the strand for accurate DNA cleavage. Base-specific recognition of the flanking DNA by conserved amino acids is revealed, defining a new role for the WVPHEL motif in mariner transposition and providing a molecular explanation for in vitro mutagenesis data. Comparison of the pre-TS cleavage and post-cleavage Mos1 transpososomes with structures of Prototype Foamy Virus intasomes suggests a binding mode for target DNA prior to Mos1 transposon integration.

Structural basis of Mos1 transposase inhibition by the anti-retroviral drug Raltegravir

DNA transposases catalyze the movement of transposons around genomes by a cut-and-paste mechanism related to retroviral integration. Transposases and retroviral integrases share a common RNaseH-like domain with a catalytic DDE/D triad that coordinates the divalent cations required for DNA cleavage and integration. The anti-retroviral drugs Raltegravir and Elvitegravir inhibit integrases by displacing viral DNA ends from the catalytic metal ions. We demonstrate that Raltegravir, but not Elvitegravir, binds to Mos1 transposase in the presence of Mg(2+) or Mn(2+), without the requirement for transposon DNA, and inhibits transposon cleavage and DNA integration in biochemical assays. Crystal structures at 1.7 Å resolution show Raltegravir, in common with integrases, coordinating two Mg(2+) or Mn(2+) ions in the Mos1 active site. However, in the absence of transposon ends, the drug adopts an unusual, compact binding mode distinct from that observed in the active site of the prototype foamy virus integrase.

Biochemical characterization and comparison of two closely related active mariner transposases

Most DNA transposons move from one genomic location to another by a cut-and-paste mechanism and are useful tools for genomic manipulations. Short inverted repeat (IR) DNA sequences marking each end of the transposon are recognized by a DNA transposase (encoded by the transposon itself). This enzyme cleaves the transposon ends and integrates them at a new genomic location. We report here a comparison of the biophysical and biochemical properties of two closely related and active mariner/Tc1 family DNA transposases: Mboumar-9 and Mos1. We compared the in vitro cleavage activities of the enzymes on their own IR sequences, as well as cross-recognition of their inverted repeat sequences. We found that, like Mos1, untagged recombinant Mboumar-9 transposase is a dimer and forms a stable complex with inverted repeat DNA in the presence of Mg²⁺ ions. Mboumar-9 transposase cleaves its inverted repeat DNA in the manner observed for Mos1 transposase. There was minimal cross-recognition of IR sequences between Mos1 and Mboumar-9 transposases, despite these enzymes having 68% identical amino acid sequences. Transposases sharing common biophysical and biochemical properties, but retaining recognition specificity toward their own IR, are a promising platform for the design of chimeric transposases with predicted and improved sequence recognition.

Biochemical and immunological characterization of Toxoplasma gondii macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a proinflammatory molecule in mammals that, unusually for a cytokine, exhibits tautomerase and oxidoreductase enzymatic activities. Homologues of this well conserved protein are found within diverse phyla including a number of parasitic organisms. Herein, we produced recombinant histidine-tagged Toxoplasma gondii MIF (TgMIF), a 12-kDa protein that lacks oxidoreductase activity but exhibits tautomerase activity with a specific activity of 19.3 μmol/min/mg that cannot be inhibited by the human MIF inhibitor ISO-1. The crystal structure of the TgMIF homotrimer has been determined to 1.82 Å, and although it has close structural homology with mammalian MIFs, it has critical differences in the tautomerase active site that account for the different inhibitor sensitivity. We also demonstrate that TgMIF can elicit IL-8 production from human peripheral blood mononuclear cells while also activating ERK MAPK pathways in murine bone marrow-derived macrophages. TgMIF may therefore play an immunomodulatory role during T. gondii infection in mammals.

Structure of a complex phosphoglycan epitope from gp72 of Trypanosoma cruzi

The parasitic protozoan organism Trypanosoma cruzi is the causative agent of Chagas disease. The insect vector-dwelling epimastigote form of the organism expresses a low abundance glycoprotein associated with the flagellum adhesion zone, called gp72. The gp72 glycoprotein was first identified with an anti-carbohydrate IgG3 monoclonal antibody called WIC29.26 and has been shown to have an unusual sugar composition. Here, we describe a new way to isolate the WIC29.26 carbohydrate epitope of gp72. Using ¹H NMR and mass spectrometry before and after derivatization, we provide an almost complete primary chemical structure for the epitope, which is that of a complex phosphosaccharide: Galfβ1–4Rhapα1–2Fucpα1-4(Galpβ1–3)(Galpα1–2)Xylpβ1–4Xylpβ1–3(Xylpβ1–2Galpα1-4(Galpβ1–3)(Rhapα1–2)Fucpα1–4)GlcNAcp, with phosphate attached to one or other of the two Galp terminal residues and in which all residues are of the d-absolute configuration, except for fucose and rhamnose which are l. Combined with previous data (Haynes, P. A., Ferguson, M. A., and Cross, G. A. (1996) Glycobiology 6, 869–878), we postulate that this complex structure and its variants lacking one or more residues are linked to Thr and Ser residues in gp72 via a phosphodiester linkage (GlcNAcpα1-P-Thr/Ser) and that these units may form phosphosaccharide repeats through GlcNAcpα1-P-Galp linkages. The gp72 glycoprotein is associated with the flagellum adhesion zone on the parasite surface, and its ligation has been implicated in inhibiting parasite differentiation from the epimastigote to the metacyclic trypomastigote stage. The detailed structure of the unique phosphosaccharide component of gp72 reported here provides a template for future biosynthetic and functional studies.

Solution conformations of early intermediates in Mos1 transposition

DNA transposases facilitate genome rearrangements by moving DNA transposons around and between genomes by a cut-and-paste mechanism. DNA transposition proceeds in an ordered series of nucleoprotein complexes that coordinate pairing and cleavage of the transposon ends and integration of the cleaved ends at a new genomic site. Transposition is initiated by transposase recognition of the inverted repeat sequences marking each transposon end. Using a combination of solution scattering and biochemical techniques, we have determined the solution conformations and stoichiometries of DNA-free Mos1 transposase and of the transposase bound to a single transposon end. We show that Mos1 transposase is an elongated homodimer in the absence of DNA and that the N-terminal 55 residues, containing the first helix-turn-helix motif, are required for dimerization. This arrangement is remarkably different from the compact, crossed architecture of the dimer in the Mos1 paired-end complex (PEC). The transposase remains elongated when bound to a single-transposon end in a pre-cleavage complex, and the DNA is bound predominantly to one transposase monomer. We propose that a conformational change in the single-end complex, involving rotation of one half of the transposase along with binding of a second transposon end, could facilitate PEC assembly.

Chemical structure of Trichomonas vaginalis surface lipoglycan: a role for short galactose (β1-4/3) N-acetylglucosamine repeats in host cell interaction

The extracellular parasite Trichomonas vaginalis contains a surface glycoconjugate that appears to mediate parasite-host cell interaction via binding to human galectin-1. This glycoconjugate also elicits cytokine production from human vaginal epithelial cells, implicating its role in modulation of host immune responses. We have analyzed the structure of this glycoconjugate, previously described to contain the sugars rhamnose (Rha), N-acetylglucosamine (GlcNAc), galactose (Gal), xylose (Xyl), N-acetylgalactosamine (GalNAc), and glucose (Glc), using gas chromatograph mass spectrometry (GC-MS), matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF), electrospray MS/MS, and nuclear magnetic resonance (NMR), combined with chemical and enzymatic digestions. Our data reveal a complex structure, named T. vaginalis lipoglycan (TvLG), that differs markedly from Leishmania lipophosphoglycan and Entamoeba lipopeptidophosphoglycan and is devoid of phosphosaccharide repeats. TvLG is composed of an α1–3 linked polyrhamnose core, where Rha residues are substituted at the 2-position with either β-Xyl or chains of, on average, five N-acetyllactosamine (-3Galβ1–4GlcNAcβ1-) (LacNAc) units and occasionally lacto-N-biose (-3Galβ1-3GlcNAcβ1-) (LNB). These chains are themselves periodically substituted at the Gal residues with Xyl-Rha. These structural analyses led us to test the role of the poly-LacNAc/LNB chains in parasite binding to host cells. We found that reduction of poly-LacNAc/LNB chains decreased the ability of TvLG to compete parasite binding to host cells. In summary, our data provide a new model for the structure of TvLG, composed of a polyrhamnose backbone with branches of Xyl and poly-LacNAc/LNB. Furthermore, the poly-LacNAc side chains are shown to be involved in parasite-host cell interaction.

Molecular architecture of the Mos1 paired-end complex: the structural basis of DNA transposition in a eukaryote

A key step in cut-and-paste DNA transposition is the pairing of transposon ends before the element is excised and inserted at a new site in its host genome. Crystallographic analyses of the paired-end complex (PEC) formed from precleaved transposon ends and the transposase of the eukaryotic element Mos1 reveals two parallel ends bound to a dimeric enzyme. The complex has a trans arrangement, with each transposon end recognized by the DNA binding region of one transposase monomer and by the active site of the other monomer. Two additional DNA duplexes in the crystal indicate likely binding sites for flanking DNA. Biochemical data provide support for a model of the target capture complex and identify Arg186 to be critical for target binding. Mixing experiments indicate that a transposase dimer initiates first-strand cleavage and suggest a pathway for PEC formation.

Structures of Leishmania major orthologues of macrophage migration inhibitory factor

Leishmania major, an intracellular parasitic protozoon that infects, differentiates and replicates within macrophages, expresses two closely related MIF-like proteins. To ascertain the roles and potential differences of these two Leishmania proteins, recombinant L. major MIF1 and MIF2 have been produced and the structures resolved by X-ray crystallography. Each has a trimeric ring architecture similar to mammalian MIF, but with some structurally distinct features. LmjMIF1, but not LmjMIF2, has tautomerase activity. LmjMIF2 is found in all life cycle stages whereas LmjMIF1 is found exclusively in amastigotes, the intracellular stage responsible for mammalian disease. The findings are consistent with parasite MIFs modulating or circumventing the host macrophage response, thereby promoting parasite survival, but suggest the LmjMIFs have potentially different biological roles. Analysis of the Leishmania braziliensis genome showed that this species lacks both MIF genes. Thus MIF is not a virulence factor in all species of Leishmania.

Cloning, expression and characterisation of FKB-6, the sole large TPR-containing immunophilin from C. elegans

We have cloned, expressed, purified and characterised ceFKB-6, the only large tetratricopeptide repeat motif-containing immunophilin in Caenorhabditis elegans which is similar to the human orthologues FKBP51 and FKBP52. It shows increased peptidyl prolyl isomerase activity, the measured k(cat)/K(m) of 1.3 x 10(6) M(-1) s(-1)is twofold greater than that of hFKBP12 and hFKBP51. NMR studies of the interaction between FKB-6 and the C-terminal DAF-21 pentapeptide MEEVD show interactions consistent with those found between the large human immunophilin TPR domains and human Hsp90. In vivo localisation studies show that the fkb-6 gene is expressed in all stages from embryo to adult with predominant expression being noted in the adult dorsal and ventral nerve cords.

Crystallization of a Mos1 transposase-inverted-repeat DNA complex: biochemical and preliminary crystallographic analyses

A complex formed between Mos1 transposase and its inverted-repeat DNA has been crystallized. The crystals diffract to 3.25 A resolution and exhibit monoclinic (P2(1)) symmetry, with unit-cell parameters a = 120.8, b = 85.1, c = 131.6 A, beta = 99.3 degrees . The X-ray diffraction data display noncrystallographic twofold symmetry and characteristic dsDNA diffraction at approximately 3.3 A. Biochemical analyses confirmed the presence of DNA and full-length protein in the crystals. The relationship between the axis of noncrystallographic symmetry, the unit-cell axes and the DNA diffraction pattern are discussed. The data are consistent with the previously proposed model of the paired-ends complex containing a dimer of the transposase.

Mechanism of Mos1 transposition: insights from structural analysis

We present the crystal structure of the catalytic domain of Mos1 transposase, a member of the Tc1/mariner family of transposases. The structure comprises an RNase H-like core, bringing together an aspartic acid triad to form the active site, capped by N- and C-terminal alpha-helices. We have solved structures with either one Mg2+ or two Mn2+ ions in the active site, consistent with a two-metal mechanism for catalysis. The lack of hairpin-stabilizing structural motifs is consistent with the absence of a hairpin intermediate in Mos1 excision. We have built a model for the DNA-binding domain of Mos1 transposase, based on the structure of the bipartite DNA-binding domain of Tc3 transposase. Combining this with the crystal structure of the catalytic domain provides a model for the paired-end complex formed between a dimer of Mos1 transposase and inverted repeat DNA. The implications for the mechanisms of first and second strand cleavage are discussed.

Trypanosoma brucei glycoproteins contain novel giant poly-N-acetyllactosamine carbohydrate chains

The flagellar pocket of the bloodstream form of the African sleeping sickness parasite Trypanosoma brucei contains material that binds the beta-d-galactose-specific lectin ricin (Brickman, M. J., and Balber, A. E. (1990) J. Protozool. 37, 219-224). Glycoproteins were solubilized from bloodstream form T. brucei cells in 8 M urea and 3% SDS and purified by ricin affinity chromatography. Essentially all binding of ricin to these glycoproteins was abrogated by treatment with peptide N-glycosidase, showing that the ricin ligands are attached to glycoproteins via N-glycosidic linkages to asparagine residues. Glycans released by peptide N-glycosidase were resolved by Bio-Gel P-4 gel filtration into two fractions: a low molecular mass mannose-rich fraction and a high molecular mass galactose and N-acetylglucosamine-rich fraction. The latter fraction was further separated by high pH anion exchange chromatography and analyzed by gas chromatography mass spectrometry, one- and two-dimensional NMR, electrospray mass spectrometry, and methylation linkage analysis. The high molecular mass ricin-binding N-glycans are based on a conventional Manalpha1-3(Manalpha1-6)Manbeta1-4-GlcNAcbeta1-4GlcNAc core structure and contain poly-N-acetyllactosamine chains. A significant proportion of these structures are extremely large and of unusual structure. They contain an average of 54 N-acetyllactosamine (Galbeta1-4GlcNAc) repeats per glycan, linked mostly by -4GlcNAcbeta1-6Galbeta1-interrepeat linkages, with an average of one -4GlcNAcbeta1-3(-4GlcNAcbeta1-6)Galbeta1- branch point in every six repeats. These structures, which also bind tomato lectin, are twice the size reported for the largest mammalian poly-N-acetyllactosamine N-linked glycans and also differ in their preponderance of -4GlcNAcbeta1-6Galbeta1- over -4GlcNacbeta1-3Galbeta1- interrepeat linkages. Molecular modeling suggests that -4GlcNAcbeta1-6Galbeta1- interrepeat linkages produce relatively compact structures that may give these giant N-linked glycans unique physicochemical properties. Fluorescence microscopy using fluorescein isothiocyanatericin indicates that ricin ligands are located mainly in the flagellar pocket and in the endosomal/lysosomal system of the trypanosome.

Expression, purification and preliminary crystallographic studies of a single-point mutant of Mos1 mariner transposase

A soluble single-point mutant of full-length Mos1 mariner transposase (MW = 40.7 kDa) has been overexpressed in Escherichia coli, purified to 95% homogeneity and crystallized. This provides the first example of the crystallization of a eukaryotic transposase. The native crystals diffract to 2.5 A resolution and show tetragonal symmetry, with unit-cell parameters a = b = 44.5, c = 205.6 A. Multiple-wavelength anomalous data from a selenomethionyl form of the protein and data from a heavy-atom derivative have been collected.

Synchrony of nutrient supply to the rumen and dietary energy source and their effects on the growth and metabolism of lambs

The objective of the current series of experiments was to assess the effects of dietary synchrony of OM and N supply to the rumen, achieved by altering the sequence of feeding individual ingredients and in diets with different energy sources, on the metabolism and performance of growing lambs. In Exp. 1, the in situ degradability coefficients of OM and N were determined for five feed ingredients and subsequently was used to formulate two diets, based either on barley or sugar beet pulp, to have a similar predicted nutrient content. Within each diet, specific ingredients were shifted between the 0900 and 1600 feeding to provide either a synchronous, intermediate, or asynchronous supply of OM and N to the rumen. In Exp. 2, these diets were fed at a restricted level to 48 growing lambs with an initial live weight of 25.1 +/- 4.22 kg and a slaughter weight of 41.4 +/- 1.94 kg. There was no significant effect of dietary treatment on live weight gain or feed conversion efficiency. Lambs fed the synchronous diets deposited more kidney knob and channel fat than lambs on the asynchronous or intermediate diets (P < 0.05), whereas lambs fed the barley-based diets deposited more carcass (P < 0.05) and noncarcass (P < 0.001) fat than lambs on the sugar beet-based diets. Lambs fed the asynchronous diets retained less energy over the course of the experiment than lambs on the intermediate or synchronous diets (P < 0.05), and had a lower energy efficiency (0.079, 0.097, and 0.093 MJ retained/ MJ of intake, respectively, P < 0.05). Lambs fed the barley-based diets retained more energy than lambs on the sugar beet-based (P < 0.001) and had a higher energy balance (0.095 vs. 0.084 MJ retained/MJ intake, respectively; P < 0.01). Plasma ammonia concentrations mirrored ruminal ammonia concentrations on the barley-based diets, but not sugar beet-based diets. In Exp. 3, lambs fed the sugar beet-based diets had a higher digestibility of OM and NDF (P < 0.001). By contrast, lambs on the barley-based diets had a higher level of purine derivative excretion and microbial N production (P < 0.001). The results indicate that neither dietary synchrony nor energy source significantly influenced growth rate. However, both the asynchronous and sugar beet pulp-based diets resulted in a lower efficiency of dietary energy use, and the avoidance of asynchronous patterns of nutrient release within the rumen can improve energy efficiency in growing lambs.

Expression, purification, and characterization of active recombinant prostate-specific antigen in Pichia pastoris (yeast)

BACKGROUND

Prostate-specific antigen (PSA), a member of the kallikrein family of serine proteases, is a chymotrypsin-like glycoprotein produced by the prostate epithelium. Elevated serum PSA (> 4 ng/ml) is a tumor marker for prostatic cancer and benign prostatic hypertrophy; increasing serum PSA over time is indicative of metastatic disease. It has been suggested that PSA may contribute to tumor metastasis through degradation of extracellular matrix glycoproteins, as well as cleavage of IGF binding protein-3, a modulator of IGF-1. To elucidate the role of PSA in the development and progression of prostatic cancer, it is necessary to have a reliable, cost-effective source of enzymatically active protein. Previous efforts to express recombinant PSA (rPSA) produced inactive proPSA, or mixtures of active and inactive PSA requiring activation by removal of the propeptide. We describe the expression of active recombinant mature PSA in yeast.

METHODS

Stable chromosomal integration of a construct consisting of the yeast alpha-factor signal sequence preceding the mature PSA sequence resulted in secretion of rPSA. The rPSA was purified from the yeast cell culture supernatant to homogeneity by strong cation-exchange chromatography, and characterized by SDS-PAGE, Western analysis, electrospray mass spectrometry, N-glycanase digestion, N-terminal amino acid sequencing, and inactivation by a PSA-specific inhibitor.

RESULTS

We report the production of active, mature rPSA in Pichia pastoris. Two forms of rPSA varying slightly in glycosylation were identified. The specific activity of the rPSA was equal to that of human seminal plasma PSA (0.56 micromol/min mg) as determined using a chromogenic substrate.

CONCLUSIONS

Large-scale production of active rPSA will be useful in the exploration of PSA effects on tumor cell proliferation, migration and metastasis. In addition, a large supply of enzyme should facilitate the discovery of novel inhibitors for in vitro and in vivo evaluation, and may provide a reproducible source of rPSA for use as a standard in diagnostic testing.

Difference in the mechanisms of the cold and heat induced unfolding of thioredoxin h from Chlamydomonas reinhardtii: spectroscopic and calorimetric studies

The thermodynamic stability and temperature induced structural changes of oxidized thioredoxin h from Chlamydomonas reinhardtii have been studied using differential scanning calorimetry (DSC), near- and far-UV circular dichroism (CD), and fluorescence spectroscopies. At neutral pH, the heat induced unfolding of thioredoxin h is irreversible. The irreversibly unfolded protein is unable to refold due to the formation of soluble high-order oligomers. In contrast, at acidic pH the heat induced unfolding of thioredoxin h is fully reversible and thus allows the thermodynamic stability of this protein to be characterized. Analysis of the heat induced unfolding at acidic pH using calorimetric and spectroscopic methods shows that the heat induced denaturation of thioredoxin h can be well approximated by a two-state transition. The unfolding of thioredoxin h is accompanied by a large heat capacity change [6.0 +/- 1.0 kJ/(mol.K)], suggesting that at low pH a cold denaturation should be observed at the above-freezing temperatures for this protein. All used methods (DSC, near-UV CD, far-UV CD, Trp fluorescence) do indeed show that thioredoxin h undergoes cold denaturation at pH <2.5. The cold denaturation of thioredoxin h cannot, however, be fitted to a two-state model of unfolding. Furthermore, according to the far-UV CD, thioredoxin h is fully unfolded at pH 2.0 and 0 degrees C, whereas the other three methods (near-UV CD, fluorescence, and DSC) indicate that under these conditions 20-30% of the protein molecules are still in the native state. Several alternative mechanisms explaining these results such as structural differences in the heat and cold denatured state ensembles and the two-domain structure of thioredoxin h are discussed.

A method for the dispersal and characterization of leukocytes from the human female reproductive tract

PROBLEM

The isolation of human female reproductive tract (RT) cells that maintain viability and are representative of the entire population is essential for a thorough evaluation of mucosal immunity in the reproductive tract mucosa. Here, we describe the isolation of RT cells in high yields and with high viability from the Fallopian tube, uterine endometrium, endocervix, ectocervix and vagina.

METHOD OF STUDY

This cell dispersion method uses an enzyme cocktail composed of pancreatin, hyaluronidase, and collagenase (PHC), and employs a 250-microm mesh screen to facilitate cell dispersion.

RESULTS

The yields of cells isolated per gram of tissue in the presence of this PHC cocktail were compared and found to be strikingly higher relative to the yields obtained with other enzyme cocktails or in the absence of enzymes. Flow cytometry was used to characterize leukocyte subsets isolated from uterine endometrium in the presence of the various enzyme cocktails. The common leukocyte antigen marker CD45, pan T-cell marker CD3, monocyte/macrophage marker CD14 and B-cell marker CD19 were retained after exposure to the PHC cocktail of enzymes. The expression of CD8 and CD4 was lost after exposure to added enzymes but regained after culture overnight.

CONCLUSION

These studies demonstrate the feasibility of using enzymatic digestion for the isolation of whole populations of Fallopian tube, endometrial, cervical and vaginal cells, including leukocyte subsets in high yields, and provide a foundation for investigating mucosal immune cell function in the human female RT.

Impact of insecticides and surfactant on lettuce physiology and yield

Insecticides are used extensively on lettuce, Lactuca sativa L., grown in southwestern Arizona because of heavy insect pressure that can potentially reduce lettuce productivity. Multiple sprays are made per season to manage these insects in lettuce. One of the major concerns related to extensive insecticide applications in lettuce is the potential subtle impact of insecticides that may reduce lettuce photosynthesis and yield. We conducted field and greenhouse experiments to examine the impact of multiple insecticides and surfactant spray applications on lettuce photosynthesis and yield. Lettuce was planted in the field in 1998, insecticides and surfactant were applied, and lettuce gas-exchange and dry weights were determined. Treatments were arranged in a split-plot consisting of insecticides as main plot and surfactant as subplot treatments in a randomized complete block design with four replications. Photosynthetic rates of lettuce were significantly reduced by endosulfan, methomyl, acephate, and surfactant at seedling stage 4 h and 2 d after the spray application was made. However, the reduction in lettuce photosynthesis by these insecticides and surfactant was only transient, and lettuce photosynthesis recovered 5 d after the spray application was made. Photosynthetic rates were not altered by zeta-cypermethrin, emamectin benzoate, and spinosad at the seedling stage. Insecticides or surfactant (Kinetic, a nonionic surfactant) did not significantly affect lettuce photosynthesis after rosette formation. In addition, lettuce dry weight was not significantly altered. These studies suggest that lettuce photosynthesis may be susceptible to some insecticides at the seedling stage. Consequently, we found that biorational insecticides, introduced to manage insect pests in lettuce, have no influence on lettuce physiology at the seedling stage, unlike the chlorinated hydrocarbons, organophosphates, or carbamates tested in this study. In a greenhouse study, we found that lettuce photosynthesis and yield were not altered by Bacillus thuringiensis application. Our results indicate that B. thuringiensis and the newer insecticides, particularly biorationals, can be used to manage lettuce insect pests without significantly altering lettuce gas-exchange and yield.

Primary structure determinants of the pH- and temperature-dependent aggregation of thioredoxin

Thioredoxins are small proteins found in all living organisms. We have previously reported that Chlamydomonas reinhardtii thioredoxin h exhibited differences both in its absorption spectrum and its aggregation properties compared to thioredoxin m. In this paper, we demonstrate, by site-directed mutagenesis, that the particularity of the absorption spectrum is linked to the presence of an additional tryptophan residue in the h isoform. The pH and temperature dependence of the aggregation of both thioredoxins has been investigated. Our results indicate that the aggregation of TRX is highly dependent on pH and that the differences between the two TRX isoforms are linked to distinct pH dependencies. We have also analyzed the pH and temperature dependence of 12 distinct variants of TRX engineered by site-directed mutagenesis. The results obtained indicate that the differences in the hydrophobic core of the two TRX isoforms do not account for the differences of aggregation. On the other hand, we show the importance of His-109 as well as the second active site cysteine, Cys-39 in the aggregation mechanism.

MEARA sequence repeat of human CstF-64 polyadenylation factor is helical in solution. A spectroscopic and calorimetric study

The primary structure of the human CstF-64 polyadenylation factor contains 12 nearly identical repeats of a consensus motif of five amino acid residues with the sequence MEAR(A/G). No known function has yet been ascribed to this motif; however, according to secondary structure prediction algorithms, it should form a helical structure in solution. To validate this theoretical prediction, we synthesized a 31 amino acid residue peptide (MEARA(6)) containing six repeats of the MEARA sequence and characterized its structure and stability by circular dichroism (CD) spectroscopy and differential scanning calorimetry (DSC). No effects of concentration on the CD or DSC properties of MEARA(6) were observed, indicating that the peptide is monomeric in solution at concentrations up to 2 mM. The far UV-CD spectra of MEARA(6) indicates that at a low temperature (1 degrees C) the MEARA(6) peptide has a relatively high helical content (76% at pH 2.0 and 65% at pH 7.0). The effects of pH and ionic strength on the CD spectrum of MEARA(6) suggest that a number of electrostatic interactions (e.g., i, i + 3 Arg/Glu ion pair, charge-dipole interactions) contribute to the stability of the helical structure in this peptide. DSC profiles show that the melting of MEARA(6) helix is accompanied by positive change in the enthalpy. To determine thermodynamic parameters of helix-coil transition from DSC profiles for this peptide, we developed a new, semiempirical procedure based on the calculated function for the heat capacity of the coiled state for a broad temperature range. The application of this approach to the partial molar heat capacity function for MEARA(6) provides the enthalpy change for helix formation calculated per amino acid residue as 3.5 kJ/mol.

Conserved cysteines in the type 1 deiodinase selenoprotein are not essential for catalytic activity

The iodothyronine deiodinases are a family of oxidoreductases that catalyze the removal of iodide from thyroid hormones. Each of the three isoforms contain selenocysteine at its active site and several cysteine residues that may be important for catalytic activity. Of particular interest in the type I deiodinase (D1) is Cys124, which is vicinal to the selenocysteine at position 126, and Cys194, which has been conserved in all deiodinases identified to date. In the present studies, we have characterized the functional properties of C124A, C194A, and C124A/C194A D1 mutants, which were prepared by site-directed mutagenesis and expressed in COS-7 cells. In broken cell preparations, the sensitivity of the mutants to the selective D1 inhibitors propylthiouracil and aurothioglucose were unaltered. Mutagenesis at the Cys124 position was associated with a 7-11-fold increase in the Km of dithiothreitol, whereas Vmax values remained largely unchanged. However, both mutations resulted in marked decreases in Vmax values when glutathione or a reconstituted thioredoxin cofactor system were used in the assay. In contrast to the results of these in vitro studies, no impairment in deiodinating capability was noted in intact cells expressing equivalent levels of the mutant constructs. These studies demonstrate that Cys124 and Cys194 influence the reactivity of the D1 with thiol cofactors in in vitro assay systems but are not determinants of the sensitivity of the enzyme to propylthiouracil and aurothioglucose. Furthermore, the observation that the cysteine mutants are fully active in intact cells demonstrates that the results of commonly used broken cell assays do not accurately predict the activity of the D1 in intact cells and suggests that glutathione and thioredoxin are not the major thiols utilized in vivo to support D1 activity.

Structure of the glycosylphosphatidylinositol membrane anchor glycan of a class-2 variant surface glycoprotein from Trypanosoma brucei

The neutral glycan fraction of the glycosylphosphatidylinositol (GPI) membrane anchor of a class-2 variant surface glycoprotein (VSG) from Trypanosoma brucei was isolated following aqueous hydrogen fluoride dephosphorylation and nitrous acid deamination of the purified glycoprotein. The neutral glycans were fractionated by high-pH anion exchange chromatography and gel-filtration and six major glycan structures were solved by a combination of one and two-dimensional NMR, composition analysis, methylation linkage analysis and electrospray-mass spectrometry. The glycans were similar to those previously described for class-1 VSGs, in that they contained the linear trimannosyl sequence Manalpha1-2Manalpha1-6Man and a complex alpha-galactose branch of up to Galalpha1-2Galalpha1-6(Galalpha1-2)Gal, but most also contained an additional galactose residue attached alpha1-2 to the non-reducing terminal mannose residue and about one-third contained an additional galactose residue attached beta1-3 to the middle mannose residue. The additional complexity of the class-2 VSG GPI glycans is discussed in terms of a biosynthetic model that explains the full range of mature GPI structures that can be expressed on different VSG classes by the same trypanosome clone.

The glycosylation of the variant surface glycoproteins and procyclic acidic repetitive proteins of Trypanosoma brucei

Trypanosoma brucei, in common with the other African trypanosomes, exhibits unusual cell-surface molecular architecture. The bloodstream form of the parasite is coated with a continuous layer of approximately five million variant surface glycoprotein (VSG) dimers that provide the parasite with a macromolecular diffusion barrier to guard against lysis by the alternative complement pathway. The procyclic form of the parasite has a more diffuse cell-surface coat made up of approximately 2.5 million copies of procyclic acidic repetitive protein (PARP). Within the VSG and PARP coats exist lower-abundance surface glycoproteins such as receptors and nutrient transporters. Both the VSG molecules and the PARP molecules are attached to the membrane via glycosylphosphatidylinositol (GPI) membrane anchors and the VSGs and one form of PARP are N-glycosylated. In this article, the structures of the N-glycans and the GPI anchors of T. brucei VSGs and PARPs are reviewed and simple models of the surfaces of bloodstream and procyclic trypomastigotes are presented.

Influence of the estrous cycle on the presence and distribution of immune cells in the rat reproductive tract

PROBLEM

Previous studies have shown that the uterus and vagina contain cells that can present antigen to ovalbumin-specific T-cells. The objective of the present study was to systematically characterize the immune cells [major histocompatibility complex (MHC) class-II+, macrophages, granulocytes, dendritic cells, and CD8+ cells] present in the uterus and vagina of the rat and to examine their distribution at various stages of the estrous cycle.

METHOD OF STUDY

Uterine and vaginal tissues from female rats were selected at various stages of the estrous cycle and were examined by immunohistochemical analysis. MHC class-II (Ia)-positive cells were detected using the OX-6 monoclonal antibody; macrophages, granulocytes, and dendritic cells were detected by OX-41 monoclonal antibody and CD8-positive T-cells were identified by OX-8 monoclonal antibody.

RESULTS

Immunohistochemical analysis showed cycle-dependent changes in the immune cell populations in the uterus and vagina. Ia+ cells, macrophages, granulocytes, and dendritic cells were present in large numbers in the stroma of the endometrium and around the glandular epithelium in the uterus at estrus, the stage of the reproductive cycle when estradiol levels are known to be high, relative to those seen at diestrus, when estrogen levels are low and progesterone is the predominant hormone. CD8+ cells were observed in the uterus interspersed between glandular epithelial cells at estrus. Immune cells were more numerous in the vagina, relative to the uterus. OX-6 and OX-41-positive cells were present in greater numbers in the subepithelial layers of the vagina at diestrus, in contrast to estrus.

CONCLUSION

This study demonstrates that a variety of immune cells are present in the reproductive tract and that their number and distribution vary in a tissue-specific manner with the stage of the estrous cycle.

Anion binding to the ubiquitin molecule

Effects of different salts (NaCl, MgCl2, CaCl2, GdmCl, NaBr, NaClO4, NaH2PO4, Na2SO4) on the stability of the ubiquitin molecule at pH 2.0 have been studied by differential scanning calorimetry, circular dichroism, and Tyr fluorescence spectroscopies. It is shown that all of the salts studied significantly increase the thermostability of the ubiquitin molecule, and that this stabilization can be interpreted in terms of anion binding. Estimated thermodynamic parameters of binding for Cl- show that this binding is relatively weak (Kd = 0.15 M) and is characterized by a negative enthalpy of -15 kJ/mol per site. Particularly surprising was the observed stabilizing effect of GdmCl through the entire concentration range studied (0.01-2 M), however, to a lesser extent than stabilization by NaCl. This stabilizing effect of GdmCl appears to arise from the binding of Cl- ions. Analysis of the observed changes in the stability of the ubiquitin molecule in the presence of GdmCl can be adequately described by combining the thermodynamic model of denaturant binding with Cl- binding effects.

Cloning, overexpression, purification, and spectroscopic characterization of human S100P

The calcium-binding protein S100P has been found to be associated with human prostate cancer. We have overexpressed S100P in Escherichia coli using a T7 expression system. A rapid two-step procedure for the isolation of overexpressed S100P leads to a preparation of >95% pure protein with a yield of approximately 150 mg per liter of culture. The structural integrity of recombinant S100P was analyzed using CD and fluorescence spectroscopic techniques. The far-UV CD shows that secondary structure of recombinant S100P consists predominantly of a-helical structure. Both near-UV CD and tyrosine fluorescence spectra show that aromatic residues are involved in the formation of a specific, well packed structure, indicating that the recombinant S100P protein adopts a compact folded conformation. Ca2+ has a profound effect on S100P structure. Near-UV CD and fluorescence intensity of both internal (tyrosine) and external (ANS) probes suggest significant structural rearrangements in the tertiary structure of the molecule. The similarity of far-UV CD spectrum of S100P in the presence and in the absence of Ca2+ suggests that Ca2+ binding has only minor effects on secondary structure.

Synthesis and characterization of insulin-fluorescein derivatives for bioanalytical applications

Human insulin was labeled with fluorescein isothiocyanate (FITC) and fully characterized to yield four distinct insulin-FITC species. High-performance liquid chromatography and electrospray mass spectrometry were used to determine the extent and location of fluorescein conjugation. By changing the reaction conditions (i.e., pH, time, and FITC/insulin ratio) the selectivity of the fluorescein conjugation was altered, and all conjugates could be separated. The isolated species of insulin-FITC were labeled at the following residues: A1(Gly), B1(Phe), A1(Gly)B1(Phe), and A1(Gly)B1(Phe)B29(Lys). All four insulin-FITC conjugates were then used to develop fluorescence polarization binding assays with monoclonal and polyclonal anti-insulin antibodies. The assay sensitivity differed between the conjugates depending on the site of modification (B1 > A1 > A1B1 > A1B1B29). Also, the type of antibody used had an important role in the binding of insulin-FITC conjugates. Finally, for the first time the biological activity of the four conjugates was demonstrated by an autophosphorylation assay. The positional substitution dramatically affected the biological activity, confirming insights into the residues responsible for the insulin binding region. The B1 conjugate was found to retain almost all biological activity while the A1 and A1B1 conjugates had approximately 10 times lower activity. The trisubstituted species (labeled at A1, B1, and B29) was determined to be least active.

Uterine stromal cell suppression of pIgR production by uterine epithelial cells in vitro: a mechanism for regulation of pIgR production

Previous studies have shown that the polymeric Ig receptor (pIgR) is produced by rat uterine epithelial cells both in vivo and vitro. The expression of the pIgR is regulated by sex hormones and/or cytokines at mucosal sites, however the mechanism of regulation in the uterus is not clear. In these studies, co-culture of stromal cells from mature rat uteri with uterine epithelial cells decreased epithelial cell pIgR production. Conditioned supernatants from stromal cells incubated with epithelial cells also decreased pIgR production. Immunohistochemical studies confirmed that expression of pIgR on uterine epithelial cells decreased in the presence of stromal cells. Viability of epithelial cells was sustained during these experiments, as evidenced by the maintenance of high transepithelial resistance. These studies are the first report of stromal cell regulation of pIgR production by epithelial cells at any site in the body and suggest that stromal cells can provide a signal that leads to the regulation of pIgR production.

Leptin is a four-helix bundle: secondary structure by NMR

Leptin is a signaling protein that in its mutant forms has been associated with obesity and Type II diabetes. The lack of sequence similarity has precluded analogies based on structural resemblance to known systems. Backbone NMR signals for mouse leptin (13C/15N -labeled) have been assigned and its secondary structure reveals it to be a four-helix bundle cytokine. Helix lengths and disulfide pattern are in agreement with leptin as a member of the short-helix cytokine family. A three-dimensional model was built verifying the mechanical consistency of the identified elements with a short-helix cytokine core.

Isolation and measurement of the endogenous cannabinoid receptor agonist, anandamide, in brain and peripheral tissues of human and rat

Anandamide (arachidonylethanolamide) is a novel lipid neurotransmitter first isolated from porcine brain which has been shown to be a functional agonist for the cannabinoid CB1 and CB2 receptors. Anandamide has never been isolated from human brain or peripheral tissues and its role in human physiology has not been examined. Anandamide was measured by LC/MS/MS and was found in human and rat hippocampus (and human parahippocampal cortex), striatum, and cerebellum, brain areas known to express high levels of CB1 cannabinoid receptors. Significant levels of anandamide were also found in the thalamus which expresses low levels of CB1 receptors. Anandamide was also found in human and rat spleen which expresses high levels of the CB2 cannabinoid receptor. Small amounts of anandamide were also detected in human heart and rat skin. Only trace quantities were detected in pooled human serum, plasma, and CSF. The distribution of anandamide in human brain and spleen supports its potential role as an endogenous agonist in central and peripheral tissues. The low levels found in serum, plasma, and CSF suggest that it is metabolized in tissues where it is synthesized, and that its action is probably not hormonal in nature.

The lipid structure of the glycosylphosphatidylinositol-anchored mucin-like sialic acid acceptors of Trypanosoma cruzi changes during parasite differentiation from epimastigotes to infective metacyclic trypomastigote forms

The major acceptors of sialic acid on the surface of metacyclic trypomastigotes, which are the infective forms of Trypanosoma cruzi found in the insect vector, are mucin-like glycoproteins linked to the parasite membrane via glycosylphosphatidylinositol anchors. Here we have compared the lipid and the carbohydrate structure of the glycosylphosphatidylinositol anchors and the O-linked oligosaccharides of the mucins isolated from metacyclic trypomastigotes and noninfective epimastigote forms obtained in culture. The single difference found was in the lipid structure. While the phosphatidylinositol moiety of the epimastigote mucins contains mainly 1-O-hexadecyl-2-O-hexadecanoylphosphatidylinositol, the phosphatidylinositol moiety of the metacyclic trypomastigote mucins contains mostly (approximately 70%) inositol phosphoceramides, consisting of a C18:0 sphinganine long chain base and mainly C24:0 and C16:0 fatty acids. The remaining 30% of the metacyclic phosphatidylinositol moieties are the same alkylacylphosphatidylinositol species found in epimastigotes. In contrast, the glycosylphosphatidylinositol glycan cores of both molecules are very similar, mainly Man alpha 1-2Man alpha 1-2Man alpha 1- 6Man alpha 1-4GlcN. The glycans are substituted at the GlcN residue and at the third alpha Man distal to the GlcN residue by ethanolamine phosphate or 2-aminoethylphosphonate groups. The structures of the desialylated O-linked oligosaccharides of the metacyclic trypomastigote mucin-like molecules, released by beta-elimination with concomitant reduction, are identical to the structures reported for the epimastigote mucins (Previato, J. O., Jones, C., Gonçalves, L. P. B., Wait, R., Travassos, L. R., and Mendoça-Previato, L. (1994) Biochem. J. 301, 151-159). In addition, a significant amount of nonsubstituted N-acetylglucosaminitol was released from the mucins of both forms of the parasite. Taken together, these results indicate that when epimastigotes transform into infective metacyclic trypomastigotes, the phosphatidylinositol moiety of the glycosylphosphatidylinositol anchor of the major acceptor of sialic acid is modified, while the glycosylphosphatidylinositol anchor and O-linked sugar chains remain essentially unchanged.

Solution dynamics of the oligosaccharide moiety of ganglioside GM1: comparison of solution conformations with the bound state conformation in association with cholera toxin B-pentamer

The solution dynamics of the oligosaccharide moiety of ganglioside GM1 have been determined by use of a combination of 1H rotating frame Overhauser effect measurements and restrained molecular dynamics simulations. It is found that the Galbeta1-3 and NeuNAc moieties which are primarily recognized by cholera toxin both exhibit considerable torsional flexibility about their respective glycosidic linkages. A comparison with the bound state conformation of the ganglioside in association with cholera toxin B-pentamer, shows that a low energy conformation of the oligosaccharide, which closely approximates the global minimum, is selected upon binding.

Polymeric immunoglobin (Ig) receptor production and IgA transcytosis in polarized primary cultures of mature rat uterine epithelial cells

These studies were conducted to more fully understand the role of uterine epithelial cells (UEC) in immunoglobin (Ig)A movement from tissue into secretions in the female reproductive tract. Indirect immunofluorescence and image analysis showed that the polymeric Ig receptor (pIgR), which is responsible for transporting polymeric IgA (pIgA) across epithelial cells, was expressed in uterine tissues from rats throughout the estrous cycle. UEC pIgR levels were higher at estrus than at either proestrus or diestrus. When UEC were isolated from the uteri of adult rats and grown on cell culture inserts, cells grew to confluence, formed tight junctions, and released secretory component (SC), the external domain of the pIgR, into the apical medium. Irrespective of whether UEC were isolated from the uteri of rats at the diestrous, proestrous, or estrous stages of the reproductive cycle, cells produced SC, indicating that they are capable of IgA transport. 125I-IgA was preferentially transcytosed from the basolateral to the apical surface, demonstrating that dimeric IgA (dIgA) could be transported by UEC in culture. In contrast, the fluid phase marker [3H]inulin moved at a comparable rate in both directions across the cell monolayer. 125I-IgA transport through UEC was saturable and specific for pIgA in that unlabeled pIgA, but not IgG, inhibited 125I-dIgA transcytosis from the basolateral to the apical surface. Immunoprecipitation of 125I-IgA in the apical chamber with rabbit anti-SC antibody indicated that after transepithelial movement, IgA was bound to SC. Northern blot analysis of RNA extracted from UEC demonstrated that cells continued to synthesize pIgR mRNA in culture. Our results suggest that in the uterus, epithelial cells play a key regulatory role in the control of IgA transcytosis from tissue into secretions.

Decreased axial and peripheral bone density in patients taking long-term warfarin

Impaired vitamin K metabolism is associated with under-carboxylation of the non-collagenous bone-matrix protein osteocalcin, which is required in its fully carboxylated state for normal bone formation. Post-menopausal women have under-carboxylation of osteocalcin which increases with age and is marked in the elderly. A similarly marked degree of impaired carboxylation occurs during coumarin therapy, and a key question is whether this may lead to accelerated loss of bone mass which is clinically important. We measured axial and peripheral bone mineral density (BMD) in 40 male patients on warfarin and 40 controls individually matched for age, disease and other drug therapy. A consistent trend for reduced BMD at all sites was observed in the warfarin-treated patients. This was particularly marked in the cancellous bone at the distal radius (9% reduction, p = 0.023) and at the cancellous rich lumbar spine site (10.4% reduction, p < 0.004). No significant relationship was observed between warfarin dose, International Normalized Ratio (INR) or duration of therapy and bone density. Because of the biochemical similarity, this study provides a new lead on post-menopausal osteoporosis, and supports the hypothesis that impaired carboxylation of osteocalcin plays a role in the pathogenesis of bone loss in the elderly through deficiency in vitamin K metabolism.

Regulation of polymeric immunoglobulin A receptor messenger ribonucleic acid expression in rodent uteri: effect of sex hormones

Previously we have shown that estradiol stimulates the production of secretory component, the external domain of the polymeric immunoglobulin A (IgA) receptor (pIgR) responsible for transporting IgA from tissues into secretions. In the present study, levels of pIgR messenger RNA (mRNA) in uterine tissues of rats were correlated with pIgR expression in epithelial cells and secretory component in uterine secretions. Analysis of uterine pIgR mRNA and pIgR expression in epithelial cells during the estrous cycle indicated that levels were high at proestrus and estrus and low at diestrus. When ovariectomized rats were treated with estradiol for 3 days, and pIgR mRNA was measured 4 and 12 h after the last injection, levels of uterine pIgR mRNA were significantly greater than those in saline-treated controls. High levels of pIgR were also detected in uterine epithelial cells and uterine secretions. When estradiol and progesterone were given in combination, progesterone partially reversed the effect of estradiol on pIgR mRNA levels and expression of pIgR in epithelial cells. These studies demonstrate that changes in uterine pIgR mRNA levels correlate with pIgR expression during the estrous cycle and in response to estradiol and progesterone. These findings suggest that mucosal immune responses in the reproductive tract are regulated in part by the actions of estradiol and progesterone on pIgR mRNA expression.