The TIR-domain containing effectors BtpA and BtpB from Brucella abortus impact NAD metabolism

Abstract

Brucella species are facultative intracellular Gram-negative bacteria relevant to animal and human health. Their ability to establish an intracellular niche and subvert host cell pathways to their advantage depends on the delivery of bacterial effector proteins through a type IV secretion system. Brucella Toll/Interleukin-1 Receptor (TIR)-domain-containing proteins BtpA (also known as TcpB) and BtpB are among such effectors. Although divergent in primary sequence, they interfere with Toll-like receptor (TLR) signaling to inhibit the innate immune responses. However, the molecular mechanisms implicated still remain unclear. To gain insight into the functions of BtpA and BtpB, we expressed them in the budding yeast Saccharomyces cerevisiae as a eukaryotic cell model. We found that both effectors were cytotoxic and that their respective TIR domains were necessary and sufficient for yeast growth inhibition. Growth arrest was concomitant with actin depolymerization, endocytic block and a general decrease in kinase activity in the cell, suggesting a failure in energetic metabolism. Indeed, levels of ATP and NAD + were low in yeast cells expressing BtpA and BtpB TIR domains, consistent with the recently described enzymatic activity of some TIR domains as NAD + hydrolases. In human epithelial cells, both BtpA and BtpB expression reduced intracellular total NAD levels. In infected cells, both BtpA and BtpB contributed to reduction of total NAD, indicating that their NAD + hydrolase functions are active intracellularly during infection. Overall, combining the yeast model together with mammalian cells and infection studies our results show that BtpA and BtpB modulate energy metabolism in host cells through NAD + hydrolysis, assigning a novel role for these TIR domain-containing effectors in Brucella pathogenesis.

Regulation of Expression of the TIR-Containing Protein C Gene of the Uropathogenic Escherichia coli Strain CFT073

“…The TIR domains of bacterial TIR containing proteins including TcpC and TcpB were recently shown to act as NAD + hydrolases [ 19 , 26 ]. Overexpression of the TIR domain of TcpC reduced the intracellular bacterial concentration of NAD + [ 19 ].…”

Klebsiella pneumoniaehijacks the Toll-IL-1R protein SARM1 in a type I IFN-dependent manner to antagonize host immunity

“…The evidence of this study suggests that K. pneumoniae leverages the TIR-TIR interactions between SARM1, and MyD88 and TRIF to attenuate MyD88 and TRIF-dependent inflammatory responses. There are few examples of pathogens exploiting TIR-TIR interactions to blunt the activation of TLR-controlled signalling pathways (Askarian et al, 2014;Cirl et al, 2008;Coronas-Serna et al, 2020;Imbert et al, 2017;Xiong et al, 2019). However, and without exception, these pathogens deploy a prokaryotic protein containing the TIR domain into immune cells, whereas K. pneumoniae is the first pathogen hijacking an endogenous mammalian TIR-containing protein.…”

“…The presence of this domain indicates a role in IL1 and TLR signalling. Interestingly, bacterial proteins containing the TIR domain interfere with TLR signalling to inhibit innate immune responses (Askarian et al, 2014;Cirl et al, 2008;Coronas-Serna et al, 2020;Imbert et al, 2017;Xiong et al, 2019). It is intriguing that the SARM1 TIR domain is more closely related to bacteria TIR proteins than to the other mammalian TIR containing adaptors .…”

The SARM1 TIR NADase: Mechanistic Similarities to Bacterial Phage Defense and Toxin-Antitoxin Systems

“…The newly discovered bacterial TIR domain NADases also participate in phage defense as they are essential components of the Thoeris phage defense mechanism (43,44). Moreover, bacteria not only use TIR NADases to defend against phage invasion, but also to disrupt mammalian innate immune mechanisms via metabolic disruption of the host cell (45). In addition, plant TIR domain innate immune receptors are active NADases and this enzymatic function is essential for the cell death that confers disease resistance (20,(46)(47)(48).…”