The PII protein interacts with the Amt ammonium transport and modulates nitrate/nitrite assimilation in mycobacteria

Abstract

PII proteins are signal transduction proteins that belong to a widely distributedfamily of proteins involved in the modulation of different metabolisms in bacteria.These proteins are homotrimers carrying a flexible loop, named T-loop, whichchanges its conformation due to the recognition of diverse key metabolites,ADP, ATP, and 2-oxoglutarate. PII proteins interact with different partners toprimarily regulate a set of nitrogen pathways. In some organisms, PII proteinscan also control carbon metabolism by interacting with the biotin carboxylcarrier protein (BCCP), a key component of the acetyl-CoA carboxylase (ACC)enzyme complex, inhibiting its activity with the consequent reduction of fattyacid biosynthesis. Most bacteria contain at least two PII proteins, named GlnBand GlnK, with different regulatory roles. In mycobacteria, only one PII proteinwas identified, and the three-dimensional structure was solved, however, itsphysiological role is unknown. In this study we purified the Mycobacteriumtuberculosis (M. tb) PII protein, named GlnB, and showed that it weakly interactswith the AccA3 protein, the α subunit shared by the three different, and essential,Acyl-CoA carboxylase complexes (ACCase 4, 5, and 6) present in M. tb. A M.smegmatis deletion mutant, ΔMsPII, exhibited a growth deficiency on nitrateand nitrite as unique nitrogen sources, and accumulated nitrite in the culturesupernatant. In addition, M. tb PII protein was able to interact with the C-terminaldomain of the ammonium transporter Amt establishing the ancestral role forthis PII protein as a GlnK functioning protein.