Analysis of the mature protein predicted a molecular weight mass of 13.6 kDa. Positions 31 and 32 of the precursor protein contain the sequence Ala-x-Ala, a motif commonly found preceding the cleavage site 25. The Rv1419p contains a carbohydrate-binding B-chain ricin domain and belongs to the ricin-type β-trefoil family of proteins, which is composed of three homologous subdomains as well as the presence

of a Q-W pattern 26. B-chain ricin domains have been demonstrated to bind cell surface glycolipids and glycoproteins bearing β-1,4-linked galactose and mannose moieties 27. In addition, database searching GPCR Compound Library datasheet has shown that the Rv1419 ORF displays 100% identity with its homologue from the clinical strain Mtb CDC1551 (GenBank accession number: AE000516.2) as well as M. bovis BCG (GenBank accession number: AM408590.1) and 78% identity to M. marinum (GenBank accession number: CP000854.1) as well Y27632 as M. ulcerans (Genbank accession number: CP000325.1) homologous gene (Table 1). These data suggest the existence of a previously uncharacterized secreted carbohydrate-binding protein from Mtb and related sequences in other mycobacteria. To further study possible functions of Rv1419 gene product, we have produced a recombinant protein as described in the Materials and methods section. A DNA fragment

of 496 bp was obtained (Fig. 1B), purified, and cloned into the vector pMOSBlue. Sequencing procedure confirmed that cloning and amplification experiments generated an unaltered Rv1419 sequence (data not shown). The fragment was then inserted in-frame with the start codon present at NdeI cleavage site into the plasmid pET15b enabling full production of Rv1419-gene product Aspartate using Escherichia coli. Figure 1C shows a typical SDS-PAGE experiment of the obtained recombinant Rv1419p demonstrating a single band with molecular weight of ∼17 kDa. Additionally, we have confirmed that Rv1419p possesses lectin activity based on classical erythrocyte agglutination assays (Fig. 1D). Following bidimensional gel analysis and mass spectrometry

of CFP from Mtb H37Rv, Malen et al. have recently detected a spot corresponding to the Rv1419 gene product 13. To further investigate whether Rv1419p is secreted and/or expressed in other Mtb compartments, we have generated a mAb (clone 276.B7/IgG1Kappa) against this protein. Figure 2A reveals a single ∼13 kDa band in CFP preparations from Mtb H37Rv, but not in the CFP fractions obtained from the non-tuberculous mycobacteria species M. avium, M. kansasii, M. fortuitum. Compared with the Mtb CFP, the whole cell lysate, cell wall, or membrane preparations presented lower amounts of a similar ∼13 kDa band following incubation with the mAb (Fig. 2B). In contrast, as previously demonstrated 28, high levels of the 19 kDa lipoprotein corresponding band from Mtb H37Rv were observed in the studied fractions incubated with an anti-19 kDa lipoprotein mAb (Fig. 2B).