Guanosine pentaphosphate

  • PpGpp
  • Guanosine -5 ', 3'- tetraphosphate

Fixed

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Guanosine -3 ', 5'- bispyrophosphat or ppGpp is the signal molecule, a bacterial stress response, the so-called stringent response. It is a derivative of Guanosindiphosphats carrying an additional pyrophosphate at the 3 ' atom of the ribose.

PpGpp was first discovered in Escherichia coli. E. coli ppGpp is an indicator for a lack of nutrients.

PpGpp cycle

In E. coli, the precursor molecule pppGpp is made of two ppGpp synthetases from ATP and GTP, RelA and SPOT. RelA can also be produced directly ppGpp. A 5'- phosphohydrolase cleaves the phosphate residue of pppGpp. RelA is bound by the ribosome, acting as a sensor for uncharged tRNAs and synthesized pppGpp at amino acid deficiency. SPOT is a cytosolic protein and synthesized pppGpp in glucose deficiency. In contrast to RelA Spot ppGpp reduces to pyrophosphate and GDP. The DNA sequences of the relA and spoT genes of E. coli are similar, so it is paralogous genes. In the N- terminus, however, find differences, the so-called HD domain; which occurs in hydrolases, is mutated in the relA gene. Therefore RelA ppGpp can not degrade.

Function

PpGpp binds to RNA polymerase and has a profound effect on the transcription of various genes. Reducing the rate of transcription of the rRNA genes, and induce the transcription of genes that are involved in amino acid biosynthesis. ppGpp is a global regulator of gene expression in E. coli.

PpGpp in other bacteria

In contrast to E. coli and other bacteria include some bacteria, such as Bacillus subtilis, and many other gram-positive bacteria, only a single ppGpp metabolizing enzyme that produces ppGpp and degrades. In many pathogenic bacteria ppGpp plays an important role as a global regulator of gene expression. In these bacteria, ppGpp is even identified as a virulence factor:

Thus, the ppGpp synthesis a previously unidentified, possible target for novel antibiotics dar. In Streptomyces coelicolor and other streptomycetes ppGpp is required for antibiotic biosynthesis. In rhizobia ppGpp is essential for symbiosis between bacteria and plant and for nitrogen fixation. In archaea ppGpp has not been established.

PpGpp in plants

PpGpp is also found in plants. It is synthesized in the chloroplast, and also plays an important role in the adaptation to a changing environment.

CAS registry number PubChem DrugBank Guanosine diphosphate Adenosine triphosphate Guanosine triphosphate RNA-Polymerase Proceedings of the National Academy of Sciences of the United States of America Digital Object Identifier Cell (journal)
284301
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