Centrosomin Self-Assembly and Centrosomal Protein Recruitment



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Centrosomes, the major microtubule organizing centers in animal cells, are important for mitotic spindle formation. Normally, each cell has two centrosomes which migrate to opposite sides of the nuclear envelope prior to entry into mitosis. Centrosomin (Cnn) is a major centrosomal protein that is important for nucleation and organization of bipolar spindle microtubules at mitosis. Cnn protein localizes to the pericentriolar matrix and from there other centrosomal proteins 'load' onto the centrosome, including gamma-tubulin. Centrosomes are non-functional without the addition of Cnn since it is responsible for recruitment of other centrosomal proteins. There are two conserved motifs in Cnn protein, currently of unknown function. One of these motifs is most likely responsible for interaction with gamma-tubulin and other centrosomal proteins which make the centrosome capable for microtubule nucleation. Cnn full-length and half proteins were expressed in E. coli and purified in vitro. The properties of these Cnn proteins show self-assembly and recruitment of centrosomal proteins. These activities of Cnn in vitro are novel and will help further the investigation of Cnn protein function in the context of biological systems. Cnn fusion proteins show characteristics similar to centrosomal 'satellite' or 'flare' particles described in animal cells. It is likely that these satellites communicate with the actin cytoskeleton in syncytial Drosophila embryos.