Tubulinlike protein from Spirochaeta bajacaliforniensis

Tubulin proteins are the fundamental subunits of all polymeric microtubule-based eukaryotic structures. Long, hollow structures each composed of 13 protofilaments as revealed by electron microscopy, microtubules (240 angstroms in diameter) are nearly ubiquitous in eukaryotes. These proteins have been the subject of intense biochemical and biophyiscal interest since the early 1970s and are of evolutionary interest as well. If tubulin-based structures (i.e., neurotubules, mitotic spindle tubules, centrioles, kinetosomes, axonemes, etc.) evolved from spirochetes by way of motility symbioses, tubulin homologies with spirochete proteins should be detectable. Tubulin proteins are widely thought to be limited to eukaryotes. Yet both azotobacters and spirochetes have shown immunological cross-reactivity with antitubulin antibodies. In neither of these studies was tubulin isolated nor any specific antigen identified as responsible for the immunoreactivity. Furthermore, although far less uniform in structure than eukaryotic microtubules, various cytoplasmic fibers and tubules (as seen by electron microscopy) have been reported in several types of prokaryotes (e.g., Spirochaeta; large termite spirochetes; treponemes; cyanobacteria; and Azotobacter. This work forms a part of our long-range study of the possible prokaryotic origin of tubulin and microtubules. Spirochetes are helically shaped gram-negative motile prokaryotes. They differ from all other bacterial in that the position of their flagella is periplasmic: their flagella lie between the inner and outer membranes of the gram-negative cell wall. Some of the largest spirochetes have longitudinally aligned 240 angstrom microtubules. Unfortunately, in spite of many attempts, all of the larger spirochetes (family Pillotaceae) with well-defined cytoplasmic tubules and antitubulin immunoreactivity are not cultivable. However, a newly described spirochete species (Spirochaeta bajacaliforniensis) possessing cytoplasmic fibers displays antitubulin immunoreactivity in whole-cell preparations. Since preliminary observations suggested that Spirochaeta bajacaliforniensis proteins may be related to eukaryotic tubulins, their characterization was undertaken. Brain tubulin can be purified by utilizing its ability to polymerize at warm temperatures and to depolymerize in the cold. After several cycles of sedimentation and redissolution the microtubule fraction is comprised of 75% tubulin and 20% high molecular mass microtubule-associated proteins (MAPs). In this paper we report that components of cell lysates, prepared from a spirochete that contains cytoplasmic fibers (Spirochaeta bajacaliforniensis), also exhibit the property of temperature-dependent cyclical sedimentation. Additionally we report the identification and characterization of the polypeptide responsible for cross-reactivity with antitubulin antiserum.

Detection of serum IgG antibodies specific for Wolbachia surface protein in rhesus monkeys infected with Brugia malayi

The mechanism of lymphedema development in individuals with lymphatic filariasis is presently poorly understood. To investigate whether Wolbachia, symbiotic bacteria living within filarial nematodes, may be involved in disease progression, Wolbachia-specific immune responses were assayed in a group of Brugia malayi-infected rhesus monkeys. Serum IgG antibodies specific for a major Wolbachia surface protein (WSP) were detected in 2 of 12 infected monkeys. It is interesting that both of these monkeys developed lymphedema after becoming amicrofilaremic. WSP-specific antibody responses were temporally associated with increases in antifilarial IgG1 antibodies as well as lymphedema development. These findings suggest that Wolbachia may be important in understanding disease caused by filarial worms.

Determination of Wolbachia genome size by pulsed-field gel electrophoresis

Genome sizes of six different Wolbachia strains from insect and nematode hosts have been determined by pulsed-field gel electrophoresis of purified DNA both before and after digestion with rare-cutting restriction endonucleases. Enzymes SmaI, ApaI, AscI, and FseI cleaved the studied Wolbachia strains at a small number of sites and were used for the determination of the genome sizes of wMelPop, wMel, and wMelCS (each 1.36 Mb), wRi (1.66 Mb), wBma (1.1 Mb), and wDim (0.95 Mb). The Wolbachia genomes studied were all much smaller than the genomes of free-living bacteria such as Escherichia coli (4.7 Mb), as is typical for obligate intracellular bacteria. There was considerable genome size variability among Wolbachia strains, especially between the more parasitic A group Wolbachia infections of insects and the mutualistic C and D group infections of nematodes. The studies described here found no evidence for extrachromosomal plasmid DNA in any of the strains examined. They also indicated that the Wolbachia genome is circular.

Drosophila hormone receptor 38 functions in metamorphosis: a role in adult cuticle formation

DHR38 is a member of the steroid receptor superfamily in Drosophila homologous to the vertebrate NGFI-B-type orphan receptors. In addition to binding to specific response elements as a monomer, DHR38 interacts with the USP component of the ecdysone receptor complex in vitro, in yeast and in a cell line, suggesting that DHR38 might modulate ecdysone-triggered signals in the fly. We characterized the molecular structure and expression of the Dhr38 gene and initiated an in vivo analysis of its function(s) in development. The Dhr38 transcription unit spans more than 40 kb in length, includes four introns, and produces at least four mRNA isoforms differentially expressed in development; two of these are greatly enriched in the pupal stage and encode nested polypeptides. We characterized four alleles of Dhr38: a P-element enchancer trap line, l(2)02306, which shows exclusively epidermal staining in the late larval, pre-pupal and pupal stages, and three EMS-induced alleles. Dhr38 alleles cause localized fragility and rupturing of the adult cuticle, demonstrating that Dhr38 plays an important role in late stages of epidermal metamorphosis.

Characterization and partial cloning of ecdysteroid receptor from a cotton boll weevil embryonic cell line

A cell line derived from the embryos of the cotton boll weevil, Anthonomus grandis (BRL-AG-2), was used to study morphological and biochemical responses to 20-hydroxyecdysone (20E). The cells respond to 10(-6) M 20E by inhibition of cell growth and enhanced production of some secreted proteins. Crude nuclear extracts containing the ecdysteroid receptor complex proteins consisting of the ecdysteroid receptor (EcR) and ultraspiracle (USP) bound ponasterone A with a Kd of 6.1 nM. Bound radiolabeled ponasterone A was displaced by both 20E and the lepidopteran-specific non-steroidal ecdysteroid agonist, RH-5992, with 41- and about 1,900-fold higher Kd values, respectively. We identified the ecdysteroid receptor components in this cell line, using monoclonal antibodies against the Drosophila ecdysteroid receptor (DmEcR) and ultraspiracle (DmUSP) proteins. A predominant band of about 70 kDa was-detected with anti-EcR, and multiple bands ranging from 50-55 kDa were detected with anti-USP in the A. grandis extracts. Using degenerate primer RT-PCR, we isolated a 450 bp cDNA fragment of the putative AgEcR. Using this fragment as a probe, we identified a large mRNA of ca. 10 kb by Northern blot analysis. These results demonstrate the usefulness of this cell line for the study of ecdysone response and the isolation of the receptor components in A. grandis.

Drosophila hormone receptor 38: a second partner for Drosophila USP suggests an unexpected role for nuclear receptors of the nerve growth factor-induced protein B type

In Drosophila the response to the hormone ecdysone is mediated in part by Ultraspiracle (USP) and ecdysone receptor (EcR), which are members of the nuclear receptor superfamily. Heterodimers of these proteins bind to ecdysone response elements (EcREs) and ecdysone to modulate transcription. Herein we describe Drosophila hormone receptor 38 (DHR38) and Bombyx hormone receptor 38 (BHR38), two insect homologues of rat nerve growth factor-induced protein B (NGFI-B). Although members of the NGFI-B family are thought to function exclusively as monomers, we show that DHR38 and BHR38 in fact interact strongly with USP and that this interaction is evolutionarily conserved. DHR38 can compete in vitro against EcR for dimerization with USP and consequently disrupt EcR-USP binding to an EcRE. Moreover, transfection experiments in Schneider cells show that DHR38 can affect ecdysone-dependent transcription. This suggests that DHR38 plays a role in the ecdysone response and that more generally NGFI-B type receptors may be able to function as heterodimers with retinoid X receptor type receptors in regulating transcription.

Cloning and developmental expression of the ecdysone receptor gene from the spruce budworm, Choristoneura fumiferana

Degenerate oligonucleotides were designed on the basis of conserved amino acid sequences in the DNA and ligand-binding regions of the members of the steroid hormone receptor superfamily. Using these oligonucleotides in RNA-PCR, a cDNA fragment was isolated from the spruce budworm, Choristoneura fumiferana. Comparison of the deduced amino acid sequence of this cDNA fragment with the members of the steroid hormone receptor superfamily suggested that this PCR fragment is a region of the ecdysone receptor from C. fumiferana. Using this cDNA fragment as a probe, 10 clones were isolated from a cDNA library that was constructed using the RNA from 4- and 5-day old embryos of C. fumiferana. Two cDNA clones (1.3 and 3 kb) that overlap and show amino acid identity with Drosophila melanogaster ecdysone receptor B-1 isoform (DmEcR) were characterized and sequenced. The longest open reading frame had 539 codons and covered the complete EcR coding region. The deduced amino acid sequence of this open reading frame had all five of the regions typical for a steroid hormone nuclear receptor. The C domain or DNA binding region showed the highest identity wit EcR proteins from D. melanogaster, Chironomus tendons, Aedes aegypti, Manduca sexta, and Bombyx mori. The A/B region, D domain or hinge region, E domain, or ligand binding region also showed significant amino acid similarity with the EcR proteins from the five insects mentioned above. The C. fumiferana ecdysteroid receptor (CfEcR) cDNA probe detected a 6.0-kb mRNA that was present throughout the development of C. fumiferana. The CfEcR mRNA increases in abundance at the time of the ecdysteroid peak during the molting phase in the embryonic, larval and pupal stages but remains low during the intermolt period. In the 6th instar larvae, the 6-kb CfEcR mRNA was detected in the epidermis, fat body, and midgut and maximum expression was observed during the prepupal peak of ecdysteroids in the hemolymph. CfEcR mRNA was induced in ecdysone treated CF-203 cells as well in the epidermis and midgut of larvae that were fed the nonsteroidal ecdysteroid agonist, RH-5992. The induction occurred within an hour and reached maximum levels around 3 hr, after which it decreased to the basal level by 6 hr. In vitro transcription and translation of the CfEcR cDNA yielded a 67-Kda protein that bound to the ecdysone response element (EcRE) as a heterodimer, along with the ultraspiracle protein.

BmCF1, a Bombyx mori RXR-type receptor related to the Drosophila ultraspiracle

A PCR approach has been used to obtain an ovarian cDNA clone from the silkmoth Bombyx mori, encoding a 50 kDa protein (BmCF1) that belongs to the RXR subfamily of nuclear hormone receptors and is most similar to the CF1/USP protein (DmCF1) encoded by the ultraspiracle gene of Drosophila. The similarity is high in the DNA-binding and moderately so in the ligand-binding domains, although not in the N-terminal, putatively activator A/B domain. Protein sequence comparisons with the available RXR sequences indicate that although insect USP-like sequences are more related to each other than to vertebrate RXRs, their inter se similarities are lower than in the case of the vertebrate RXRs. Two distinct BmCF1-homologous transcripts are observed consistently, and are indicative either of alternative splicing or of the existence of a second RXR gene in the moth. The transcripts are widely distributed, suggesting functions at multiple developmental stages, as in the case of Drosophila ultraspiracle.

The 'tubulin-like' S1 protein of Spirochaeta is a member of the hsp65 stress protein family

A 65-kDa protein (called S1) from Spirochaeta bajacaliforniensis was identified as 'tubulin-like' because it cross-reacted with at least four different antisera raised against tubulin and was isolated, with a co-polymerizing 45-kDa protein, by warm-cold cycling procedures used to purify tubulin from mammalian brain. Furthermore, at least three genera of non-cultivable symbiotic spirochetes (Pillotina, Diplocalyx, and Hollandina) that contain conspicuous 24-nm cytoplasmic tubules displayed a strong fluorescence in situ when treated with polyclonal antisera raised against tubulin. Here we summarize results that lead to the conclusion that this 65-kDa protein has no homology to tubulin. S1 is an hsp65 stress protein homologue. Hsp65 is a highly immunogenic family of hsp60 proteins which includes the 65-kDa antigens of Mycobacterium tuberculosis (an active component of Freund's complete adjuvant), Borrelia, Treponema, Chlamydia, Legionella, and Salmonella. The hsp60s, also known as chaperonins, include E. coli GroEL, mitochondrial and chloroplast chaperonins, the pea aphid 'symbionin' and many other proteins involved in protein folding and the stress response.

Binding site selection analysis of protein-DNA interactions via solid phase sequencing of oligonucleotide mixtures

By combining the concept of degenerate oligonucleotide mutagenesis (1,2,3,4) and the convenience of solid phase chemical DNA sequencing (5), we have developed a rapid procedure for determining the specificity of DNA-binding proteins in vitro. Starting with a degenerate oligonucleotide mixture, the technique assays for alternative nucleotides in fractions that are bound or non-bound to the protein of interest. In contrast to previous approaches using degenerate oligonucleotides, it does not involve cloning but rather employs direct sequencing of the oligonucleotide mixtures after attachment to a solid support. Solid state processing obviates the need for both DNA extractions from polyacrylamide gels and time-consuming ethanol precipitations. Because of its convenience and sensitivity, this binding site selection analysis is well suited to determining rapidly the sequence preference of DNA-binding proteins that are available in small amounts, and complements well established approaches like methylation interference or missing contact assays. The solid phase reaction protocol we propose can also improve these latter approaches.