High Energy Accelerator Research Organization, Japan
Toshiya Senda has completed his PhD from Nagaoka University of Technology (Niigata, Japan) in 1995. He was a research associate in Nagaoka University of Technology (1995-2001) and a senior researcher in Institute of Advanced Industrial Science and Technology (2001-2012). Now, he is the director/professor of Structural Biology Research Center of High Energy Accelerator Research Organization in JAPAN. He was awarded the CrSJ (Crystallographic society of Japan) award in 2014 (Structural biology studies of CagA from Helicobacter pylori and histone chaperon CIA/ASF1).
GTP is an energy molecule in the cell and required in protein synthesis . R eduction of GTP concentration results in slow cell growth; inversely, rapidly growing cells have elevated GTP concentration. Because of its vital roles in cell growth, GTP concentration should be monitored and homeostatically regulated in the cell. However, a sensing mech anism of cellular GTP concentration remains elusive. Here, we show that a lipid kinase , PI5P4Kβ , ser ves as a GTP sensor and GTP concentration functions as a met abolic cue via PI5P4Kβ. Our proteomics and biochemical study revealed that PI5P4Kβ binds GTP and its enzyme activity is significantly higher with GTP than with ATP; PI5P4Kβ mainly utilizes GTP for phosphorylation of PI5P. Furthermore, the kinetic characters of PI5P4Kβ are suitable to detect the change of cellular GTP concentration. These biochemical characteristics suggested that PI5P4Kβ is a GTP sensor in the cell. However, since PI5P4K β can utilize not only GTP but also ATP for the enzyme reaction in the cell, a simple knock out/down experiment is insufficient to analyze the biological function of the GTP-sensing activity of PI5P4Kβ. We therefore took a structural reverse genetic approach. First, we determined crystal structures of PI5P4Kβ-ATP/GTP complexes and used the crystal structures to prepare a PI5P4Kβ mutant that lacks GTP-sensing activity without changing ATP-dependent activity . We then preformed b iological and metabolomic analyses with the PI5P4Kβ mutant, revealing that PI5P4Kβ serves as a GTP-sensor. The GTP-sensing activity of PI5P4Kβ is critical for metabolic adaptation and tumorigenesis.