Ricerc@Sapienza

Until recently ammonia (NH3) has been known merely as a metabolic waste product, it is now emerging as key regulatory molecule, contributing to different patho-physiological processes. NH3 is produced at high concentration in the human gastrointestinal tract, in the same niche occupied by E.coli. Along with NO, CO and H2S, NH3 is both a gasotransmitter and a known inhibitor of mitochondrial haem-copper oxidase, the effect of NH3 on bacterial terminal oxidases being yet unknown.

The E. coli respiratory chain is branched and relies on three terminal oxidases, a haem-copper, cytochrome bo3, and the two bd-type oxidases, bd-I and bd-II. This prompted us to address the following question: how can E. coli survive in the human intestine, if NH3 inhibits the oxidases? Our working hypothesis is that a bd-type oxidase, could be more resistant to NH3 inhibition than a haem-copper oxidase (cytochrome bo3).

Relevant to human pathophysiology, cytochrome bd oxidases are key respiratory enzymes in many bacteria living inside humans and, in some pathogens, they promote bacterial virulence, making these enzymes of interest also as potential drug targets. In collaboration with Vitaly Borisov (Moscow State University), we contributed to show that cytochrome bd confers resistance to oxidative and nitrosative stress. Interestingly, this oxidase promotes also bacterial respiration and growth in the sulphide rich environments like the human gut.

This project aims at expanding these studies to the reaction mechanisms between terminal oxidases and gaseous molecules, particularly NH3, and their patho-physiological relevance.
Research will focus on E.coli oxidases, used as models, as well as on the bd oxidase from a gut pathogen, S. flexneri, either purified or expressed in cells. Particular emphasis will be given to bd oxidases, to better understand the role played by this enzyme within the framework of host-microbiota relationships.