SpoT
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| Bifunctional (p)ppGpp synthase/hydrolase SpoT | |||||||
|---|---|---|---|---|---|---|---|
 Predicted structure of bifunctional (p)ppGpp synthase/hydrolase SpoT. Dark blue areas represent very high model confidence (pLDDT > 90). Light blue areas represent moderate model confidence (90>pLDDT > 70). Yellow areas represent low model confidence (70>pLDDT > 50). Orange areas represent very low model confidence (pLDDT < 50).[1][2] | |||||||
| Identifiers | |||||||
| Organism | |||||||
| Symbol | spoT | ||||||
| UniProt | P0AG24 | ||||||
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Bifunctional (p)ppGpp synthase/hydrolase SpoT or SpoT is a regulatory enzyme in the RelA/SpoT Homologue (RSH) protein family that synthesizes and hydrolyzes (p)ppGpp to regulate the bacterial stringent response to environmental stressors.[3] SpoT is considered a "long" form RSH protein and is found in many bacteria and plant chloroplasts.[4] SpoT and its homologues have been studied in bacterial model organism E.coli for their role in the production and degradation of (p)ppGpp in the stringent response pathway.
Role as a Hydrolase
The stringent response regulated by SpoT, RelA, and their homologues can cause a bacterium to increase its persistence in stressful environments.[5] SpoT can act as both a hydrolase and a synthetase to (p)ppGpp alarmones in the stringent response pathway with Mn2+ as its cofactor.[6] When there are environmental stressors present, SpoT uses ATP and GDP to synthesize (p)ppGpp and catalyze the stringent response.[7] When stressors are removed and a stringent response is no longer necessary SpoT hydrolyzes (p)ppGpp, cleaving it into GTP and diphosphate.[7] Environmental stressors including but not limited to amino acid starvation,[3] carbon deficiencies,[8] phosphate deficiencies[9] and changes in temperature[4] have been documented to cause the gene encoding SpoT to activate.
The acyl carrier protein (ACP) binds to the TGS domain of SpoT; this binding is probably influenced by the ratio of unacylated ACP to acylated ACP in the cell.[10]
SpoT mainly serves as a hydrolase in systems similar to E.coli. SpoT's hydrolase activity is Mn2+-dependent with a conserved His-Asp (HD) motif.[11] Phosphate starvation is sensed by SpoT hydrolase to elevate (p)ppGpp, which induces IraP, a RssB antiadaptor that antagonizes RssB activation of RpoS turnover, thereby inducing RpoS.[9]
SpoT in E. coli
In E. coli, the SpoT protein consists of 702 amino acids.[6] E.coli uses RelA and SpoT as its two main (p)ppGpp regulating enzymes.[12] When the gene for encoding RelA is nonfunctional, E. coli can still regulate (p)ppGpp through SpoT as it has both HD and SYNTH domains.
