Microtubule cytoskeleton is an essential scaffold that functions for organizing various of cellular activities, such as highly efficient intracellular transport. In animal cells, centrosome is the primary microtubule-organizing center, which requires γ-tubulin that is present in a ring-shape macromolecular protein complex, called the γ-tubulin ring complex (γ-TuRC), to serve as a template for microtubule growth. CDK5RAP2 is recognized as a strong activator of γ-TuRC-mediated microtubule nucleation. Mutations of human CDK5RAP2 cause autosomal recessive primary microcephaly of which patients develop small brain. Until now, how the CDK5RAP2 activation of γ-TuRCs is controlled remains unclear. CDK5RAP2 contains a conserved γ-TuRC-binding domain (γ-TuNA). In my study, I found a highl...[ Read more ]

Microtubule cytoskeleton is an essential scaffold that functions for organizing various of cellular activities, such as highly efficient intracellular transport. In animal cells, centrosome is the primary microtubule-organizing center, which requires γ-tubulin that is present in a ring-shape macromolecular protein complex, called the γ-tubulin ring complex (γ-TuRC), to serve as a template for microtubule growth. CDK5RAP2 is recognized as a strong activator of γ-TuRC-mediated microtubule nucleation. Mutations of human CDK5RAP2 cause autosomal recessive primary microcephaly of which patients develop small brain. Until now, how the CDK5RAP2 activation of γ-TuRCs is controlled remains unclear. CDK5RAP2 contains a conserved γ-TuRC-binding domain (γ-TuNA). In my study, I found a highly conserved region (referred as region B) next to the γ-TuNA in CDK5RAP2 inhibited the interaction of γ-TuNA with γ-TuRC. By mutational approach, I found a conserved Ile within region B is crucial for the inhibitory function. Next, region B shows robust interaction with the γ-TuNA, which may prevent the interaction between γ-TuNA and γ-TuRC. Furthermore, by crosslinking method, calmodulin was identified as the direct binding partner of γ-TuNA. And calmodulin also shows interaction with region B. So calmodulin may also be included in the regulation of inhibitory function. To control the auto-inhibition, my preliminary studies have also suggested that this autoinhibitory mechanism might involve protein phosphorylation. Altogether, I have identified for the first time an inhibitory mechanism to regulate the interaction between the γ-TuRC and CDK5RAP2, and this mechanism may play an important role in the control of microtubule organization.