Role of TlyA in the Biology of Uncultivable Mycobacteria.

TlyA proteins are related to distinct functions in a diverse spectrum of bacterial pathogens, including mycobacterial spp. There are several annotated proteins that function as hemolysin or pore-forming molecules that play an important role in the virulence of pathogenic organisms. Many studies reported the dual activity of mycobacterial TlyA as 'hemolysin' and 'Sadenosylmethionine dependent rRNA methylase'. To act as a hemolysin, a sequence must have a signal sequence and transmembrane segment, which helps the protein enter the extracellular environment. Interestingly, the mycobacterial tlyA has neither traditional signal sequences of general/ sec/tat pathways nor any transmembrane segments. Still, it can reach the extracellular milieu with the help of non-classical signal mechanisms. Also, retention of tlyA in cultivable mycobacterial pathogens (such as Mycobacterium tuberculosis and M. marinum) as well as uncultivated mycobacterial pathogens despite their extreme reductive evolution (such as M. leprae, M. lepromatosis and M. uberis) suggests its crucial role in the evolutionary biology of pathogenic mycobacteria. Numerous virulence factors have been characterised by the uncultivable mycobacteria, but the information of TlyA protein is still limited in terms of molecular and structural characterisation. The genomic insights offered by comparative analysis of TlyA sequences and their conserved domains reveal pore-forming activity, which further confirms its role as a virulence protein, particularly in uncultivable mycobacteria. Therefore, this review presents a comparative analysis of the mycobacterial TlyA family by sequence homology and alignment to improve our understanding of this unconventional hemolysin and RNA methyltransferase TlyA of uncultivable mycobacteria.

TlyA protein of Mycobacterium leprae: a probable bio-marker of active infection.

The extent of pathogenicity of the mycobacterial infections depends on virulence factors that mediate survival inside macrophages. Virulence factors are generally believed to be specific for pathogenic species and mutated/non-functional in nonpathogenic strains. Mycobacterial TlyA can modulate the phagolysosome maturation pathway, immediately after entry into macrophages. Over-expression of open reading frame (ORF) ML1358 (tlyA) in tissues of leprosy patients by partial DNA chip and real time PCR analysis during active infection attracted our interest to explore the properties of this gene at molecular and serological levels, to understand its role in the host. Molecular properties were studied by cloning and expression of the corresponding gene in pASK-iba 43(þ) expression vector in E. coli and bioinformatics tools while sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and ELISA were applied to investigate the serological significance of rTlyA protein in different clinical states of leprosy. We observed that TlyA has a close relation among mycobacteria with specific protein domains in slow growing intracellular adapted pathogenic species. The presence of trans-membrane domains indicates its association to the cell membrane. The study revealed its highly significant sero-reactivity (P value , 0·001) in borderline lepromatous (BL) patients, and those with reversal reaction (RR) and erythema nodosum leprosum (ENL). Its role in active infection, association with the cell membrane, presence in pathogenic species and high sero-reactivity, suggested the tlyA gene as a strong disease progression marker.

Effect of listeriolysin O-loaded erythrocytes on Mycobacterium avium replication within macrophages.

OBJECTIVE: To evaluate the efficacy of erythrocytes loaded with the haemolytic toxin listeriolysin O against Mycobacterium avium replication within human macrophages. METHODS: Recombinant listeriolysin O was loaded in human erythrocytes by a procedure of hypotonic dialysis and isotonic resealing. Loaded erythrocytes were modified to allow them to be recognized and taken up by human macrophages infected with M. avium. The antimycobacterial activity of the erythrocytes loaded with listeriolysin O was evaluated by supernatant and intracellular cfu counts on days 4 and 7 post-erythrocyte administration. RESULTS: Recombinant listeriolysin O was encapsulated in human erythrocytes to reach final concentrations ranging from 1 to 4 ng/mL of erythrocytes. Erythrocytes loaded with increasing quantities of recombinant protein were able to reduce (at most by 50%) M. avium replication in a dose-dependent fashion when administered to infected macrophages. CONCLUSIONS: Erythrocytes loaded with listeriolysin O are effective against M. avium replication within macrophages. We are confident that the strategy presented could be useful against mycobacteria other than M. avium (such as Mycobacterium tuberculosis and Mycobacterium leprae) by itself or as part of an antimycobacterial treatment.

Characterization of a haemolysin from Mycobacterium tuberculosis with homology to a virulence factor of Serpulina hyodysenteriae.

Scrutiny of sequence data from the Mycobacterium leprae genome sequencing project identified the presence of a gene encoding a 268-amino-acid polypeptide which is highly similar to a pore-forming haemolysin/cytotoxin virulence determinant, TlyA, from the swine pathogen Serpulina hyodysenteriae. Using degenerate oligonucleotide primers based on the TlyA sequences, the Mycobacterium tuberculosis homologue was amplified and this product was used to obtain the clone and sequence a 2.5 kb fragment containing the whole M. tuberculosis tlyA gene. tlyA encodes a 267-amino-acid protein with a predicted molecular mass of 28 kDa. TlyA homologues were identified by PCR in M. leprae, Mycobacterium avium and Mycobacterium bovis BCG, but appeared absent in Mycobacterium smegmatis, Mycobacterium vaccae, Mycobacterium kansasii, Mycobacterium chelonae and Mycobacterium phlei. The M. tuberculosis gene appeared to be the first gene in an operon containing at least two other genes. Introduction of the M. tuberculosis tlyA gene into M. smegmatis using a mycobacterial shuttle expression plasmid converted non-haemolytic cells into those exhibiting significant haemolytic activity. Similarly, inducible haemolytic activity was observed in sonicated bacteria when tlyA was expressed as a His6-tagged fusion protein in Escherichia coli. tlyA mRNA was detected in both M. tuberculosis and M. bovis BCG using RT-PCR, confirming that this gene is expressed in organisms cultured in vitro.