Solution NMR assignment of the cryptic sixth TOG domain of mini spindles

TACC3-ch-TOG interaction regulates spindle microtubule assembly by controlling centrosomal recruitment of γ-TuRC

γ-Tubulin ring complex (γ-TuRC), composed of γ-tubulin and multiple γ-tubulin complex proteins (GCPs), serves as the major microtubule nucleating complex in animal cells. However, several γ-TuRC-associated proteins have been shown to control its function. Centrosomal adaptor protein, TACC3, is one such γ-TuRC-interacting factor that is essential for proper mitotic spindle assembly across organisms. ch-TOG is another microtubule assembly promoting protein, which interacts with TACC3 and cooperates in mitotic spindle assembly. However, the mechanism how TACC3-ch-TOG interaction regulates microtubule assembly and the γ-TuRC functions at the centrosomes remain unclear. Here, we show that deletion of the ch-TOG-binding region in TACC3 enhances recruitment of the γ-TuRC proteins to centrosomes and aggravates spindle microtubule assembly in human cells. Loss of TACC3-ch-TOG binding imparts stabilization on TACC3 interaction with the γ-TuRC proteins and it does so by stimulating TACC3 phosphorylation and thereby enhancing phospho-TACC3 recruitment to the centrosomes. We also show that localization of ch-TOG at the centrosomes is substantially reduced and the same on the spindle microtubules is increased in its TACC3-unbound condition. Additional results reveal that ch-TOG depletion stimulates γ-tubulin localization on the spindles without significantly affecting the centrosomal γ-tubulin level. The results indicate that ch-TOG binding to TACC3 controls TACC3 phosphorylation and TACC3-mediated stabilization of the γ-TuRCs at the centrosomes. They also implicate that the spatio-temporal control of TACC3 phosphorylation via ch-TOG-binding ensures mitotic spindle assembly to the optimal level.

Development of a Potential Yeast-Based Vaccine Platform for Theileria parva Infection in Cattle

East Coast Fever (ECF), caused by the tick-borne apicomplexan parasite Theileria parva, remains one of the most important livestock diseases in sub-Saharan Africa with more than 1 million cattle dying from infection every year. Disease prevention relies on the so-called "Infection and Treatment Method" (ITM), which is costly, complex, laborious, difficult to standardise on a commercial scale and results in a parasite strain-specific, MHC class I-restricted cytotoxic T cell response. We therefore attempted to develop a safe, affordable, stable, orally applicable and potent subunit vaccine for ECF using five different T. parva schizont antigens (Tp1, Tp2, Tp9, Tp10 and N36) and Saccharomyces cerevisiae as an expression platform. Full-length Tp2 and Tp9 as well as fragments of Tp1 were successfully expressed on the surface of S. cerevisiae. In vitro analyses highlighted that recombinant yeast expressing Tp2 can elicit IFNγ responses using PBMCs from ITM-immunized calves, while Tp2 and Tp9 induced IFNγ responses from enriched bovine CD8⁺ T cells. A subsequent in vivo study showed that oral administration of heat-inactivated, freeze-dried yeast stably expressing Tp2 increased total murine serum IgG over time, but more importantly, induced Tp2-specific serum IgG antibodies in individual mice compared to the control group. While these results will require subsequent experiments to verify induction of protection in neonatal calves, our data indicates that oral application of yeast expressing Theileria antigens could provide an affordable and easy vaccination platform for sub-Saharan Africa. Evaluation of antigen-specific cellular immune responses, especially cytotoxic CD8⁺ T cell immunity in cattle will further contribute to the development of a yeast-based vaccine for ECF.

Solution NMR assignment of the C-terminal domain of human chTOG

The microtubule regulatory protein colonic and hepatic tumor overexpressed gene (chTOG), also known as cytoskeleleton associated protein 5 (CKAP5) plays an important role in organizing the cytoskeleton and in particular in the assembly of k-fibres in mitosis. Recently, we dissected the hitherto poorly understood C-terminus of this protein by discovering two new domains-a cryptic TOG domain (TOG6) and a smaller, helical domain at the very C-terminus. It was shown that the C-terminal domain is important for the interaction with the TACC domain in TACC3 during the assembly of k-fibres in a ternary complex that also includes clathrin. Here we now present the solution NMR assignment of the chTOG C-terminal domain which confirms our earlier prediction that it is mainly made of α-helices. However, the appearance of the ¹H-¹⁵N HSQC spectrum is indicative of the presence of a considerable amount of unstructured and possibly flexible portions of protein in the domain.

XMAP215 is a microtubule nucleation factor that functions synergistically with the γ-tubulin ring complex

How microtubules (MTs) are generated in the cell is a major question in understanding how the cytoskeleton is assembled. For several decades, γ-tubulin has been accepted as the universal MT nucleator of the cell. Although there is evidence that γ-tubulin complexes are not the sole MT nucleators, identification of other nucleation factors has proven difficult. Here, we report that the well-characterized MT polymerase XMAP215 (chTOG/Msps/Stu2p/Alp14/Dis1 homologue) is essential for MT nucleation in Xenopus egg extracts. The concentration of XMAP215 determines the extent of MT nucleation. Even though XMAP215 and the γ-tubulin ring complex (γ-TuRC) possess minimal nucleation activity individually, together, these factors synergistically stimulate MT nucleation in vitro. The amino-terminal TOG domains 1-5 of XMAP215 bind to αβ-tubulin and promote MT polymerization, whereas the conserved carboxy terminus is required for efficient MT nucleation and directly binds to γ-tubulin. In summary, XMAP215 and γ-TuRC together function as the principal nucleation module that generates MTs in cells.