Structural Biology

Biography

Biography: Toshiya Senda

Abstract

      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.