Characterization of Mce4A protein of Mycobacterium tuberculosis: role in invasion and survival.
BACKGROUND
The mce4 operon is one of the four homologues of mammalian cell entry (mce) operons of Mycobacterium tuberculosis. The mce4A (Rv3499c) gene within this operon is homologous to mce1A (Rv0169), that has a role in host cell invasion by M. tuberculosis. Our earlier reports show that mce4 operon is expressed during the stationary phase of growth of the bacillus in culture and during the course of infection in mammalian hosts. M. tuberculosis carrying mutation in mce4 operon shows growth defect and reduced survival in infected mice. However, the intracellular localization of Mce4A protein and its direct role in cell entry or survival of the bacillus has not been demonstrated so far.


RESULTS
By transmission electron microscopy we have demonstrated that recombinant Mce4A protein facilitates the invasion of non-pathogenic strain of E. coli into non-phagocytic HeLa cells. We observe that mce4A gene has a role comparable to mce1A in the survival of recombinant E. coli in human macrophages. Using antibodies raised against Mce4A protein, we show that the protein is localized in the cell wall fraction of M. tuberculosis H37Rv stationary phase culture only.


CONCLUSIONS
Mce4A protein is expressed during the stationary phase of broth culture and localizes in the cell wall fraction of M. tuberculosis. Mce4A protein expressed in non-pathogenic E. coli enables it to enter and survive within HeLa cells and the macrophages. As Mce4A protein is expressed during later phase of mycobacterial growth, our results raise the possibility of it playing a role in maintenance of persistent tubercular infection.
Saini
Neeraj Kumar
NK
Department of Microbiology, Vallabhbhai Patel Chest Institute, University of Delhi, Delhi, India. neeraj_k_saini@yahoo.co.in
Sharma
Monika
M
Chandolia
Amita
A
Pasricha
Rashmi
R
Brahmachari
Vani
V
Bose
Mridula
M
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D005798:Genes, Bacterial; D006367:HeLa Cells; D006801:Humans; D008264:Macrophages / Q000382:microbiology*; D046529:Microscopy, Electron, Transmission; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D009876:Operon; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014376:Tuberculosis / Q000382:microbiology*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C510664:Mce4A protein, Mycobacterium tuberculosis; D011994:Recombinant Proteins; C473802:mammalian cell entry protein Mce1A, Mycobacterium tuberculosis