PII protein modelates nitrogen metabolism in Mycobacteria

DELFINA ENSINCK; GAGO GABRIELA; LUCIANO F. HUERGO; GRAMAJO HUGO; DIACOVICH LAUTARO

Beaver Run, Breckenridge, CO, USA

Simposio; A Research Reboot of Tuberculosis on The Keystone Symposia 50th Anniversary; 2022

Keystone Symposia

Mycobacteria are responsible for a large diversity of infectious diseases, including tuberculosis, one of the leading causes of death worldwide. These bacteria are able to survive in harsh environments thanks to their versatile metabolism. Therefore, understanding the complex network that coordinates the metabolic adaptations in different growth conditions would provide us with valuable information for the efforts to control tuberculosis.In bacteria such as Escherichia coli, PII proteins modulate metabolism through protein-protein interactions with enzymes, transmembrane channels, and transcription factors. This family of signal transduction proteins senses levels of α-ketoglutarate, ATP, and ADP, which indicates the carbon, nitrogen, and energy status. The binding of these allosteric effectors results in different conformational states and, consequently, in the interaction with a specific group of target proteins, most of which are involved in the nitrogen assimilation pathway. Furthermore, in some organisms, GlnB orthologs (PII family members) modulate carbon metabolism by interacting with the acetyl-CoA carboxylase complex and reducing its activity. During nitrogen starvation, Mycobacterium smegmatis and the pathogen Mycobacterium tuberculosis induce the expression of a PII protein; however, its role is still undetermined.By subcellular fractioning of extracts of M. smegmatis, we have observed that PII protein is located only in supernatant when grown in low ammonia but partially retained at the membrane after an ammonia shock. This result indicates that mycobacterial PII conserves its role of modulating the ammonia channel Amt. In addition, we have built a mutant strain of Mycobacterium smegmatis in which the PII gene was deleted. This strain exhibits normal growth when cultured in limiting concentrations ammonia. Nontheless, PII mutant showed lower growth rates in comparison to the wild-type strain when grown in nitrate or nitrite as sole nitrogen source. This result suggests that PII may be involved in nitrate and nitrite assimilation and/or nitrite detoxification. Regarding the modulation of carbon metabolism, PII proteins do not regulate the acyl-CoA activity in mycobacteria, as there is not modification in acetyl-CoA and propionyl-CoA activity in protein extracts of M. smegmatis grown in an ammonia limiting condition, and after an ammonia shock. Further research is required for a better understanding of PII role in these organisms.