Cloning and studying the role of mycobacterium tuberculosis multicopper oxidase in inhibiting the respiratory burst.

Abstract

Mycobacterium tuberculosis is the etiological agent of the pulmonary disease Tuberculosis. It affects more than one-third of the world’s population. During bacterial infections, macrophages and other phagocytic cells of the immune system target and neutralize the causative agent. Following phagocytic uptake of bacteria by the macrophages, the phagolysosomal compartment produces reactive oxygen species (ROS) through the so-called respiratory burst to control the infection. Recent work by several groups indicates that pathogenic M. tuberculosis can survive phagocytic uptake by macrophages through inhibition of the respiratory burst. I have cloned and expressed Rv0846c, a protein known to be a membrane-associated multi-copper oxidase from M. tuberculosis (MmcO). I hypothesised that MmcO suppresses the production of ROS and may thus contribute to the survival of the pathogen during phagocytosis. Purified MmcO displayed a significant activity against the model substrate ABTS. Various amounts of active MmcO were tested against the ROS production in THP-1 monocyte cell line. Streptolysin-Opermeabilized THP-1 cells that were exposed to 500 ng of the purified MmcO protein displayed asignificant reduction in the level of induced ROS by phorbol 12-myristate 13-acetate (PMA). This study indicates that the MmcO has a potential role as a virulence factor for M. tuberculosis.