No description available.

No description available.

No description available.

Oncoprotein18 (Op18) is a 19 kDa cytosolic phosphoprotein critical for cell growth and differentiation. Unphosphorylated Op18 associates with £\£]-tubulin heterodimer to form 2 tubulin-1 stathmin T2S complex and promotes microtubule catastrophe in interphase. Numerous cellular signals activate downstream protein kinases result in the phosphorylation of Ser16, Ser25, Ser38 and Ser 63 residues in Op18 that lowers its affinity for tubulin thereby increases the stability of microtubule and facilitates the formation of spindle during mitosis. Here, we found in addition to phosphorylation, Op18 could also be ubiquitin modified in vivo. An expression plasmid encodes for mutant EGFP-Op18-M5K protein whose potential lysine residues K42, K53, K75, K104, and K119 were mutated to arginines was generated to investigate the effect of ubiquitin modification of Op18 on the tubulin polymerization. Our results revealed a decrease of ubiquitin modification of mutant EGFP-Op18-M5K in comparison with that of wildtype EGFP-Op18. The expression of mutant but not the wildtype Op18 resulted in a significant increase of polymerized tubulin in mitotic cell implying that they might exhibit differential tubulin binding affinity. Moreover, the result of western blotting showed that the mutant Op18 detected in the mitotic cell corresponds to the phosphorylated version of Op18. In summary, these results imply the ubiquitination of Op18 might interfere with its phosphorylation and decrease its tubulin binding potential, thereby facilitates the polymerization of tubulin in mitotic cells. The in vitro tubulin polymerization assay will be performed to further confirm the above finding.

Transient Receptor Potential Melastatin 2 (TRPM2) is a widely expressed, non-selective cationic channel with implicated roles in cell death, chemokine production and oxidative stress. This study characterizes a novel interactor of TRPM2. Using fusion proteins comprised of the TRPM2 C-terminus we established that tubulin interacted directly with the predicted C-terminal coiled-coil domain of the channel. In vitro studies revealed increased interaction between tubulin and TRPM2 during LPS-induced macrophage activation and taxol-induced microtubule stabilization. We propose that the stabilization of microtubules in activated macrophages enhances the interaction of tubulin with TRPM2 resulting in the gating and/or localization of the channel resulting in a contribution to increased intracellular calcium and downstream production of chemokines.

Transient Receptor Potential Melastatin 2 (TRPM2) is a widely expressed, non-selective cationic channel with implicated roles in cell death, chemokine production and oxidative stress. This study characterizes a novel interactor of TRPM2. Using fusion proteins comprised of the TRPM2 C-terminus we established that tubulin interacted directly with the predicted C-terminal coiled-coil domain of the channel. In vitro studies revealed increased interaction between tubulin and TRPM2 during LPS-induced macrophage activation and taxol-induced microtubule stabilization. We propose that the stabilization of microtubules in activated macrophages enhances the interaction of tubulin with TRPM2 resulting in the gating and/or localization of the channel resulting in a contribution to increased intracellular calcium and downstream production of chemokines.

The binding kinetics of several benzimidazole compounds were determined with recombinant tubulin monomers and heterodimers from benzimidazole-sensitive and -insensitive organisms. This study utilised the naturally occurring high efficacy of the benzimdazoles for the parasitic protozoa Giardia duodenalis and Encephalitozoon intestinalis. The benzimidazoles are not active against the protozoan Cryptosporidium parvum or mammalian hosts, including humans. The affinity of several benzimidazole derivatives for monomeric and heterodimeric â-tubulin was clearly demonstrated, thus supporting previous studies of drug-resistant nematode and fungal populations. A homology model of protozoan áâ-tubulin, produced using the three-dimensionalstructure of mammalian áâ-tubulin, identified a strongly hydrophobic domain only on the â-tubulin protein of sensitive protozoa. This domain is proposed to be the benzimidazole-binding domain and the amino acid residues within it include three key residues which are substituted between benzimidazole-sensitive and –insensitive organisms. These residues are Ile-189, Val-199, and Phe-200 that all have non-polar, hydrophobic side groups and are proposed to bind with the R5 side chain of several benzimidazole derivatives. In addition to this, the benzimidazole derivatives were able to bind irreversibly with assembling microtubules from sensitive parasites. The incorporation of benzimidazole-bound áâ-heterodimers into assembling microtubules was shown to arrest polymerisation in vitro although the addition of benzimidazole compounds to assembled microtubules did not result in depolymerisation. Taken together, these results suggest that the mechanism of action of these compounds is through disruption of the dynamic equilibrium that balances the cycle of microtubule polymerisation and disintegration within these protozoa. Further, this effect is brought about by preferential binding of the benzimidazoles to a hydrophobic region on the â- tubulin protein.

Dissertation (Ph.D.).--University of Texas Graduate School of Biomedical Sciences at San Antonio, 2008. / Vita. Includes bibliographical references.

No description available.

Microtubules are critically important cytoskeletal elements. Together with microtubule associated proteins (MAPs), they form the latticework on which eukaryotic life exists. Simply put, microtubules are polymers of tubulin heterodimers, which are composed of the globular proteins alpha and beta tubulin. In vivo, these monomers associate with one another to form heterodimers, which then polymerize to form microtubules. In mammals, microtubule polymerization is a temperature-dependent process with an optimum of 37°C (Detrich et al., 2000). If temperatures exceed this optimal temperature by even a few degrees, the microtubule will begin to dissemble due to denaturation of the tubulin subunit and permanent loss of both shape and function will occur. This thermal barrier seems to be consistent in most eukaryotic organisms. Two exceptions are the thermophilic red algae, Cyanidium caldarium and Cyanidioschyzon merolae. These thermophilic acidophiles have been discovered in volcanic vents around the globe from Yellow Stone Park to Italy and grow at optimal temperatures of around 55°C. These organisms have been primarily studied in the context of evolutionary biology because of their primitive characteristics. Very little is known about the molecular biology of these organisms, and certainly nothing is known about how the biochemistry of these organisms brings about the ability to survive the harsh conditions of their environment. Currently, my hypothesis concerning the thermostable tubulin expressed within these organisms is that there may be key amino acid differences in the tubulin's primary structure that confer enhanced thermostability. I am testing this hypothesis by sequencing the alpha and beta tubulin genes of Cyanidium caldarium and Cyanidioschyzon merolae, generating homology models of the tubulin dimers, and comparing these models to a known mesophilic tubulin heterodimer structure in order to identify potential structural differences. / Master of Science