Regulation of the interaction between the microtubule organizer γ-TuRC and its stimulator CDK5RAP2

Abstract

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.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology