PgmNr Y521: Reconstitution of the microtubule nucleation system of Candida albicans.

Authors:
E. Schiebel 1 ; T. Lin 1 ; A. Neuner 1 ; D. Flemming 2 ; R. Arkowitz 3

Institutes
1) Center for Molecular Biology, University of Heidelberg, Heidelberg, DE; 2) Biochemistry Center, University of Heidelberg, Heidelberg, DE; 3) Institute of Biology Valrose, University of Nice, Nice, FR.

Keyword: Cell Cycle/Growth Control/Metabolism
Abstract:

Microtubules are hollow cylinders composed out of alpha/beta-tubulin with essential functions in cell architecture, cell movement and chromosome segregation in mitosis and meiosis. Microtubules are dynamic polymers that assemble from the heterodimer alpha/beta-tubulin in a process known as microtubule nucleation. gamma-tubulin, a member of the tubulin family, functions in microtubule nucleation by providing a template for the assembly of alpha/beta-tubulin into microtubules. How does gamma-tubulin provide this template function? gamma-tubulin assembles together with the proteins Spc97/Gcp2 and Spc98/Gcp3 into the small gamma-tubulin complex (gamma-TuSC). gamma-TuSC oligomerizes into a left-handed spiral (the alpha/beta-tubulin template) upon interaction with receptors (gamma-TuR) at the yeast spindle pole body (SPB), the microtubule organizing centre (MTOC). Spc110 is one such gamma-TuR on the nuclear side of the SPB while Spc72 has this function on the cytoplasmic side. Therefore, Spc110 and Spc72 are essential for the organization of nuclear end cytoplasmic microtubules, respectively. Budding yeast Saccharomyces cerevisiae has the simplest microtubule nucleation system of all model organisms (gamma-TuSC, Spc72 and Spc110). In Schizosaccharomyces pombe and higher eukaryotes, microtubule nucleation requires additional factors named GCP4, GCP5, GCP6, the “mitotic-spindle organizing protein associated with a ring of gamma-tubulin 1” (Mzt1) and Nedd1 (Drosophila and human cells). Interestingly, the opportunistic pathogen Candia albicans represents an intermediate between S. cerevisiae and the more complex microtubule nucleation systems of higher eukaryotes. The C. albicans genome encodes gamma-tubulin CaTUB4, CaSPC97/GCP2, CaSPC98/GCP3, the receptors CaSPC72 and CaSPC110 and MZT1. Here we report the reconstitution of the microtubule nucleation system of C. albicans with purified components and the analysis of their function in vivo. This analysis provides important insights into the function of Mzt1 and how S. cerevisiae bypassed the requirement of the normally essential MZT1 gene.