Characterization of a bifunctional enzyme with (p)pp Gpp-hydrolase/synthase activity in Leptospira interrogans.

Alarmone Guanosine 5′-diphosphate (or 5′-triphosphate) 3′-diphosphate [(p)pp Gpp] is the key component that globally regulates stringent control in bacteria. There are two homologous enzymes, Rel A and Spo T in Escherichia coli, which are responsible for fluctuations in (p)pp Gpp concentration inside the cell, whereas there exists only a single Rel A/ Spo T enzyme in Gram-positive bacteria. We have identified a bifunctional enzyme with (p)pp Gpp-hydrolase/synthase activity in Leptospira interrogans. We show that the rel Lin gene ( LA_3085) encodes a protein that fully complements the rel A/ spo T double mutants in E. coli. The protein functions as a (p)pp Gpp degradase as well as a (p)pp Gpp synthase when the cells encounter amino acid stress and deprivation of carbon sources. N-terminus HD and RSD domains of rel Lin ( rel LinN) were observed to restore growth of double mutants of E. coli. Finally, We demonstrate that purified RelLin and RelLinN show high (p)pp Gpp synthesis activity in vitro. Taken together, our results suggest that L. interrogans contain a single Rel-like bifunctional protein, RelLin, which plays an important role in maintaining the basal level of (p)pp Gpp in the cell potentially contributing to the regulation of bacterial stress response. [ABSTRACT FROM AUTHOR]

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