title: The mechanism of substrate-controlled allosteric regulation of SAMHD1 activated by GTP.
abstract: SAMHD1 is the only known eukaryotic deoxynucleoside triphosphate triphosphohydrolase (dNTPase) and is a major regulator of intracellular dNTP pools. It has been reported to be a potent inhibitor of retroviruses such as HIV-1 and endogenous retrotransposons. Previous crystal structures have revealed that SAMHD1 is activated by dGTP-dependent tetramer formation. However, recent data have indicated that the primary activator of SAMHD1 is GTP, not dGTP. Therefore, how its dNTPase activity is regulated needs to be further clarified. Here, five crystal structures of the catalytic core of SAMHD1 in complex with different combinations of GTP and dNTPs are reported, including a GTP-bound dimer and four GTP/dNTP-bound tetramers. The data show that human SAMHD1 contains two unique activator-binding sites in the allosteric pocket. The primary activator GTP binds to one site and the substrate dNTP (dATP, dCTP, dUTP or dTTP) occupies the other. Consequently, both GTP and dNTP are required for tetramer activation of the enzyme. In the absence of substrate binding, SAMHD1 adopts an inactive dimer conformation even when complexed with GTP. Furthermore, SAMHD1 activation is regulated by the concentration of dNTP. Thus, the level of dNTP pools is elegantly regulated by the self-sensing ability of SAMHD1 through a novel activation mechanism.
authors.affiliation: School of Life Sciences, Tianjin University, Tianjin, People's Republic of China.
authors.forename: Chun Feng
authors.initials: CF
authors.lastname: Zhu
authors.affiliation: School of Life Sciences, Tianjin University, Tianjin, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.affiliation: School of Life Sciences, Tianjin University, Tianjin, People's Republic of China.
authors.forename: Xin
authors.initials: X
authors.lastname: Peng
authors.affiliation: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Shijingshan District, Beijing 100049, People's Republic of China.
authors.forename: Yu Hui
authors.initials: YH
authors.lastname: Dong
authors.affiliation: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Shijingshan District, Beijing 100049, People's Republic of China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Gong
authors.affiliation: School of Life Sciences, Tianjin University, Tianjin, People's Republic of China.
authors.forename: Xiao Fang
authors.initials: XF
authors.lastname: Yu
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D006160:Guanosine Triphosphate / Q000737:chemistry*; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry*; D020836:Protein Structure, Quaternary; D000076106:SAM Domain and HD Domain-Containing Protein 1; D013329:Structure-Activity Relationship
chemical_list: D006160:Guanosine Triphosphate; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D020559:Monomeric GTP-Binding Proteins
keywords: SAMHD1; substrate-controlled allosteric regulation