Characterization of tubulin from Brugia malayi and Brugia pahangi

Two decades of antifilarial drug discovery: a review

Filariasis is one of the oldest, most debilitating, disabling, and disfiguring neglected tropical diseases with various clinical manifestations and a low rate of mortality, but has a high morbidity rate, which results in social stigma.

Purification of Trichinella spiralis tubulin: comparison of several analytic procedures

This study compares the purity indices found after purifying tubulin obtained from the nematode parasite Trichinella spiralis, using different chromatographic and electrophoretic methods. Affinity chromatography, using monoclonal antibodies anti-alpha and anti-beta-tubulin fixed to activated Sepharosa 4B-CNBr, yields a tubulin purity of 15%. In contrast, by means of interchange-anionic chromatography using a column of DEAE-Sephadex-A50, we obtained an increase in purity of up to 75%. Finally, with the combined application of preparative electrophoresis and electroelution of proteins in polyacrylamide gels with SDS, we obtained the best results with a purity reaching 90%.

Actin isoforms in the parasitic nematode Haemonchus contortus

Actin proteins in the parasitic nematode Haemonchus contortus were partially purified by a new method based on precipitation with podophyllotoxin and dimethylsulfoxide. Two-dimensional gel electrophoresis of partially purified actin proteins revealed differences in isoform composition between adults and third-stage larvae. The significance of this finding is possibly related to the existence of differential functional or developmental characteristics between these two life-cycle stages.

Characterization and biological activities of anti-Brugia pahangi tubulin monoclonal antibodies

Three monoclonal antibodies (mAb) specific to beta-tubulin were used to investigate the heterogeneity of tubulins from nematodes and mammals. Western blot analysis of one-dimensional SDS-PAGE showed that anti-Brugia pahangi tubulin mAb 1B6 and P3D react with epitope(s) specific to nematode beta-tubulin and recognize tubulin from adults and microfilariae of B. pahangi, adult B. malayi and Dirofilaria immitis, eggs of Haemonchus contortus and adult Ascaris suum. However, the same mAb did not recognize tubulin from trophozoites of Giardia lamblia, pig brain or 3T3 mouse fibroblast cells. In two-dimensional SDS-PAGE, mAb 1B6 recognized one isoform of beta-tubulin and mAb P3D recognized two beta-tubulin isoforms. Limited proteolysis showed that mAb 1B6 reacted with the amino-terminal fragments of beta-tubulin. In contrast, mAb P3D recognized the carboxy-terminal fragments of beta-tubulin. In ELISA, mAb P3D reacted with an 18 amino acid peptide corresponding to residues 430-448 of B. pahangi beta-tubulin. These observations confirm that the epitope of mAb P3D is located on the extreme carboxy-terminal region. Immunogold labelling of adult B. pahangi sections with mAb P3D revealed the presence of beta-tubulin isoforms in the cuticle, hypodermal layer and somatic muscle blocks of B. pahangi. Under in vitro conditions, mAb P3D caused 80% reduction in worm viability, during exposure over 48 h.

Fasciola hepatica: localization and partial characterization of tubulin

The localisation and distribution of the cytoskeletal protein tubulin in the adult liver fluke Fasciola hepatica have been determined by an indirect immunofluorescence technique using a monoclonal antibody raised against beta-tubulin. Tubulin was demonstrated in the tegumental syncytium and in the tegumental cell bodies and their cytoplasmic connections with the surface syncytium. Immunostaining was also evident in the nerve fibres innervating sensory receptors in the tegument, in the nerve plexus innervating the sub-tegumental musculature and in the cytoplasmic extensions of the nurse cells within the vitelline follicle. Immunoblotting of whole fluke fractions produced a single band corresponding to a molecule of approximately 54 kDa in size. This figure corresponds with previous data obtained on tubulin from other helminth and eukaryotic sources.

Identification of tubulin isoforms in different tissues of Ascaris suum using anti-tubulin monoclonal antibodies

Three monoclonal antibodies specific to alpha- and beta-tubulin were used to examine the expression of tubulin isoforms in the intestine, reproductive tract and body wall muscle of A. suum. The tubulins were found to be different in their isoelectric points, number of isoforms and peptide maps with Western blot analysis of one-dimensional polyacrylamide gel confirming the presence of alpha-, beta 1- and beta 2-tubulin. Commercial cross-reactive anti-alpha and anti-beta MAbs 356 and 357 recognized tubulin from A. suum tissues as well as from pig brain, whereas anti-A. suum beta-tubulin specific MAb P3D6 recognized tubulin from the A. suum tissues only. Two-dimensional gel analysis showed different isoform patterns in different A. suum tissues with anti-A. suum beta-tubulin MAb P3D6 and cross-reactive beta-tubulin MAb 357 recognizing 2-4 beta-tubulin isoforms and anti-alpha-tubulin MAb 356 recognizing 1-6 alpha-tubulin isoforms. Different peptide maps of tubulin were observed in the three tissues, when subjected to limited proteolysis followed by SDS-PAGE. The data indicate that different tubulins are found in different tissues of adult A. suum.

Preliminary characterization and interaction of tubulin from Trichinella spiralis larvae with benzimidazole derivatives

Tubulin was estimated to account for 0.3% of the total soluble protein in Trichinella spiralis cytosolic fractions. Tubulin from T. spiralis was partially purified by precipitation with either taxol or vinblastine sulphate. Immunoblotting with alpha- and beta-tubulin monoclonal antibodies revealed the presence of tubulin in T. spiralis partially purified preparations. Electrophoretic mobility of T. spiralis tubulin in sodium dodecyl sulphate-polyacrylamide gels was very similar to that shown by pig brain tubulin. Further studies with colchicine binding assays indicated that T. spiralis tubulin has binding features similar to that of tubulin from other nematodes: colchicine association constant = 8.1 x 10(-4) M and competitive inhibition of colchicine binding by podophyllotoxin, with an inhibition constant of 1.3 x 10(-6) M. Finally, inhibition of colchicine binding by several benzimidazoles (mebendazole, fenbendazole, oxibendazole and albendazole) was investigated. All the benzimidazoles inhibited colchicine binding in a competitive manner, with inhibition constant values ranging from 1.4 x 10(-7) M (mebendazole) to 3.9 x 10(-6) M (fenbendazole).

Characterization of a beta-tubulin gene and a beta-tubulin gene products of Brugia pahangi

A genomic clone containing a beta-tubulin gene from the parasitic nematode Brugia pahangi was isolated. This gene was sequenced to determine its size, structural organization, and corresponding primary amino acid sequence. The coding sequence of the beta-tubulin gene spans 3.8 kb, is organized into 9 exons and expresses an mNRA of 1.8 kb which codes for a protein of 448 amino acids. The predicted beta-tubulin amino acid sequence is 89%, 94%, 90% and 88% identical to the chicken beta 2, and the Caenorhabditis elegans ben-1, tub-1 and mec-7 gene products, respectively. Southern hybridization analyses demonstrated that there is only one copy of this gene isotype but that other distinct beta-tubulin genes may exist in the Brugia pahangi genome. A nematode specific antipeptide rabbit antiserum raised against the predicted amino acid sequence of the extreme carboxy-terminal region of the B. pahangi beta-tubulin was used to identify beta-tubulin isoforms in adult nematodes and microfilariae. Isoforms detected by this nematode-specific antipeptide antiserum were identical in both adult worms and microfilariae and did not differ from the isoform patterns detected by a monoclonal antibody recognizing a conserved beta-tubulin epitope. This suggests that this carboxy-terminal peptide is highly represented in the beta-tubulin isoforms of B. pahangi.

Specific interaction of benzimidazole anthelmintics with tubulin from developing stages of thiabendazole-susceptible and -resistant Haemonchus contortus

The low- and high-affinity binding of tritiated benzimidazole anthelmintics (mebendazole and oxibendazole) to tubulin-containing supernatants derived from unembryonated eggs, third stage larvae or adult worms of thiabendazole-susceptible and -resistant strains of Haemonchus contortus were examined and compared. The displacement of these radioligands by unlabelled benzimidazoles (mebendazole, fenbendazole, thiabendazole and oxibendazole) also was examined. The binding affinity, K alpha, and maximum binding, Bmax, for the high-affinity binding were calculated by non-linear least-square iterative curve fitting using a computer programme (LIGAND) based on the exact mathematical model of ligand-receptor interactions. The K alpha was of the same order of magnitude (x 10(7) M-1) for the susceptible and resistant eggs, larvae and worms. Resistance was associated with a loss of high-affinity binding. There was a 2- to 5-fold loss of Bmax by the resistant strain. The eggs showed greater high-affinity binding per milligram of protein than the larvae which, in turn, showed greater high-affinity binding than the adult worms. It was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis that the tubulin content per milligram of protein decreased from egg, through larvae to adult worm. Cross-displacement studies indicated that different benzimidazole drugs interacted with the same receptor (tubulin) and that a rank order of affinity of the benzimidazole drugs could be inferred.

Anthelmintic resistance in nematodes: extent, recent understanding and future directions for control and research

Resistance has now been reported to all of the broad spectrum anthelmintic types currently available, namely to the benzimidazoles, levamisole/morantel and to ivermectin. The problem causes most concern for parasite control in sheep, but anthelmintic resistance has also been reported in nematodes of horses, goats, pigs and more recently cattle. Our understanding of the factors which select rapidly for resistance has increased and programmes of worm control which minimize selection for anthelmintic resistance are being developed and tested. One of the greatest problems encountered in attempting to reduce the selection for overt drug resistance is the need for more sensitive tests for developing resistance. In the long term, new approaches to chemotherapy and to overcoming anthelmintic resistance problems will arise from improving our understanding of the modes of action of, and mechanisms of resistance to, anthelmintics at the level of the receptor proteins and their genes.

Diethylcarbamazine, antifilarial drug, inhibits microtubule polymerization and disrupts preformed microtubules

The effect of diethylcarbamazine (DEC) on microtubules was studied by using microtubule protein prepared from porcine brain. DEC inhibited assembly of microtubules and disassembled preformed microtubules in vitro. When the reassembled or disassembled products were examined in the presence of DEC by electron microscopy, ribbon-microtubules were frequently observed. Subsequently, the effect of DEC on the cytoplasmic microtubules complex was studied. The cells used in our study were LLC-MK2. DEC inhibited proliferation of these cells, and cells grown in the presence of DEC were likely to separate from each other and became round in shape. Immunofluorescence microscopy revealed that the cells exposed to DEC were devoid of the delicate pattern of the cytoplasmic microtubule complex.