Conformational antagonism between opposing active sites in a bifunctional RelA/SpoT homolog modulates (p)ppGpp metabolism during the stringent response [corrected].
Enzymes of the Rel/Spo family enable bacteria to survive prolonged periods of nutrient limitation by producing an intracellular signaling alarmone, (p)ppGpp, which triggers the so-called stringent response. Both the synthesis of (p)ppGpp from ATP and GDP(GTP), and its hydrolysis to GDP(GTP) and pyrophosphate, are catalyzed by Rel/Spo proteins. The 2.1 A crystal structure of the bifunctional catalytic fragment of the Rel/Spo homolog from Streptococcus dysgalactiae subsp. equisimilis, Rel(Seq), reveals two conformations of the enzyme corresponding to known reciprocal activity states: (p)ppGpp-hydrolase-OFF/(p)ppGpp-synthetase-ON and hydrolase-ON/synthetase-OFF. The hydrolase and synthetase domains bear remarkable similarities to the catalytic domains of the cyclic phosphodiesterase and nucleotidyltransferase superfamilies, respectively. The active sites, separated by more than 30 A, contain bound nucleotides including an unusual (p)ppGpp derivative, GDP-2':3'-cyclic monophosphate. Reciprocal regulation of the antagonistic catalytic activities, suggested by the structure, is supported by mutagenesis experiments and appears to involve ligand-induced signal transmission between the two active sites.
Hogg
Tanis
T
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Mechold
Undine
U
Malke
Horst
H
Cashel
Mike
M
Hilgenfeld
Rolf
R
D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology* / Q000235:genetics; D001665:Binding Sites / Q000502:physiology; D020134:Catalytic Domain / Q000502:physiology; D018360:Crystallography, X-Ray; D004734:Energy Metabolism / Q000502:physiology; D001277:GTP Pyrophosphokinase / Q000235:genetics / Q000378:metabolism*; D006158:Guanosine Pentaphosphate / Q000378:metabolism*; D008025:Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D013217:Starvation / Q000378:metabolism; D013329:Structure-Activity Relationship
D009711:Nucleotides; D006158:Guanosine Pentaphosphate; D001277:GTP Pyrophosphokinase; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases