The Ps and Qs of alarmone synthesis in Staphylococcus aureus

• Published in: PloS one Vol. 14; no. 10; p. e0213630
• Main Authors: Yang, Ning, Xie, Shujie, Tang, Nga-Yeung, Choi, Mei Yee, Wang, Ying, Watt, Rory M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15.10.2019; Public Library of Science (PLoS)
• Subjects: Amino acids; Bacteria; Bacterial Proteins - biosynthesis; Bacterial Proteins - genetics; Biochemistry; Biology and Life Sciences; Biosynthesis; Care and treatment; Cell survival; Chemical synthesis; Cloning; Dentistry; E coli; EDTA; Enzymes; Gene Expression Regulation, Bacterial - physiology; Gene Expression Regulation, Enzymologic - physiology; Genetic aspects; Gram-positive bacteria; Guanosine; Guanosine Pentaphosphate - biosynthesis; Guanosine Pentaphosphate - genetics; Homology; Hydrolysis; Ligases; Medicine and Health Sciences; Pathogens; Phosphates; Physical Sciences; Physiology; Proteins; Regulation; RelA protein; Research and analysis methods; Ribonucleic acid; Risk factors; RNA; Staphylococcus aureus; Staphylococcus aureus - genetics; Staphylococcus aureus - metabolism; Staphylococcus aureus infections; Staphylococcus infections; Streptococcus infections; Streptococcus mutans - genetics; Streptococcus mutans - metabolism; Stringent response; Hong Kong China; United States > US; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0213630

During the stringent response, bacteria synthesize guanosine-3',5'-bis(diphosphate) (ppGpp) and guanosine-5'-triphosphate 3'-diphosphate (pppGpp), which act as secondary messengers to promote cellular survival and adaptation. (p)ppGpp 'alarmones' are synthesized and/or hydrolyzed by proteins belonging to the RelA/SpoT Homologue (RSH) family. Many bacteria also encode 'small alarmone synthetase' (SAS) proteins (e.g. RelP, RelQ) which may also be capable of synthesizing a third alarmone: guanosine-5'-phosphate 3'-diphosphate (pGpp). Here, we report the biochemical properties of the Rel (RSH), RelP and RelQ proteins from Staphylococcus aureus (Sa-Rel, Sa-RelP, Sa-RelQ, respectively). Sa-Rel synthesized pppGpp more efficiently than ppGpp, but lacked the ability to produce pGpp. Sa-Rel efficiently hydrolyzed all three alarmones in a Mn(II) ion-dependent manner. The removal of the C-terminal regulatory domain of Sa-Rel increased its rate of (p)ppGpp synthesis ca. 10-fold, but had negligible effects on its rate of (pp)pGpp hydrolysis. Sa-RelP and Sa-RelQ efficiently synthesized pGpp in addition to pppGpp and ppGpp. The alarmone-synthesizing abilities of Sa-RelQ, but not Sa-RelP, were allosterically-stimulated by the addition of pppGpp, ppGpp or pGpp. The respective (pp)pGpp-synthesizing activities of Sa-RelP/Sa-RelQ were compared and contrasted with SAS homologues from Enterococcus faecalis (Ef-RelQ) and Streptococcus mutans (Sm-RelQ, Sm-RelP). Results indicated that EF-RelQ, Sm-RelQ and Sa-RelQ were functionally equivalent; but exhibited considerable variations in their respective biochemical properties, and the degrees to which alarmones and single-stranded RNA molecules allosterically modulated their respective alarmone-synthesizing activities. The respective (pp)pGpp-synthesizing capabilities of Sa-RelP and Sm-RelP proteins were inhibited by pGpp, ppGpp and pppGpp. Our results support the premise that RelP and RelQ proteins may synthesize pGpp in addition to (p)ppGpp within S. aureus and other Gram-positive bacterial species.