Impact of integrated NMR/ computation methods in solving
biological questions
Xiaoling Bao, Heng Liu, Ke Ruan, Yonghui Zhang, Zhiyong Zhang, Qi Hu, Ying Liu, Jiahai
Zhang, Qingguo Gong, Zhen Dou, Xuebiao Yao, Jihui Wu* and Yunyu Shi*
School of Life Sciences, University of Science and Technology of China, Hefei,
Anhui, 230027, People’s Republic of China
Stably transmitted genetic information through generations of living organisms
requires faithful mitotic spindle assembly and chromosome segregation.
During mitosis, the small GTPase Ran is activated to the GTP-bound form by
the guanine nucleotide exchange factor RCC1 attached to chromosome, thus
forms a steep RanGTP concentration gradient towards cytoplasm, which is
essential for proper mitotic spindle assembly. However, a mysterious
component of this molecular machinery for the maintenance of RanGTP
homeostasis has been missing for a long time. Here we present the structural
model of Ran and its nucleotide release factor hMog1 complex using nuclear
magnetic resonance (NMR) spectroscopy integrated with site-directed
mutagenesis and computational methods. Significant conformational changes
are observed upon complex formation that explains why hMog1 functions as a
nucleotide release factor rather than a nucleotide exchange factor. We show
that either hMog1 knockdown or overexpression causes chromosome
segregation errors due to the abnormal RanGTP level detected by the
RanGTP biosensor. We propose the molecular mechanism for regulating
RanGTP level by hMog1 together with RCC1 to ensure faithful mitotic spindle
assembly. Our structural and functional investigations for the first time
demonstrate that hMog1 plays an indispensable role in mitotic spindle
assembly. The deregulation of this machinery will lead to chromosome
mis-segregation, aneuploidy and eventually cancer development in human.