NAD+ Bound N‐terminal Domain of CARDS Toxin Increases IL‐1β Secretion

Abstract

Mycoplasma pneumoniae (Mp) is an atypical bacterium that is linked to various respiratory diseases such as walking pneumonia and asthma. Upon infection, Mp produces a 591‐aa virulence factor known as Community Acquired Respiratory Distress Syndrome Toxin (CARDS TX). The crystal structure of this 591‐aa cytotoxin reveals a triangular molecule comprised of an N‐terminal ADP‐ribosylating domain and a C‐terminal tandem β‐trefoil domain that is responsible for vacuolation of the host's cells. Based on structural and sequence homology to other ADP ribosylating toxins, the NAD+ binding site has been predicted, yet none of the published structures of the CARDS toxin contain NAD+. The loop connecting the N− and the C‐termini is anchored using a disulfide bond that surrounds the NAD+ binding site which might sterically hinder NAD+ binding. An N‐terminal truncation mutant (NTTM) lacking the disulfide bond has been cloned and the protein was expressed, purified and crystallization trials are underway. The NTTM was also used to treat U937 cells in presence and absence of NAD+ to test the effect of the NTTM on cytokine secretion. The data show that NTTM causes an increase in the secretion of IL‐1β and TNF‐α in presence of NAD+ suggesting an increase in the inflammatory response to the NTTM in presence of NAD+.Support or Funding InformationSt. Mary's University Biaggini Funds and The San Antonio Livestock Expedition FundsThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.