Moreover, estimated diacylglycerol modifications carrying C16 and C18 fatty acids were confirmed by neutral losses of fragments with the molecular mass of 256.24 Da and 282.44 Da, corresponding to the elimination of palmitic and oleic acid. In complemented mutant Δlnt-lntBCG_2070c, lipoproteins LprF and LppX were triacylated and glycosylated (see Additional files 6 and 7). This confirmed that BCG_2070c restored the BCG_2070c mutant. The absence of N-acylation of the four analyzed lipoproteins in the Δlnt mutant and the complementation of the mutant provide strong evidence that BCG_2070c is the only functional apolipoprotein N-acyltransferase
that modifies these lipoproteins with an amide-linked fatty acid in M. bovis BCG. In addition, it demonstrates that BCG_2279c is not able to adopt or substitute N-acylation of the four lipoproteins in the Δlnt mutant. Discussion Lipoproteins are present in all bacterial E7080 clinical trial species, but their biogenesis and lipid moieties differ, especially between Gram-negative and Gram-positive
bacteria. The three enzymes involved in lipoprotein biosynthesis, namely Lgt, LspA and Lnt first were identified in E. coli. Therefore, the lipoprotein biosynthesis pathway in E. coli is intensively studied and well described . Mycobacteria are classified as PDGFR inhibitor Gram-positive bacteria, but their lipoprotein biosynthesis pathway resembles that of Gram-negative bacteria. The discovery of Lnt in mycobacteria and the identification of lipoprotein N-acylation in M. smegmatis renewed interest within the field of mycobacterial lipoprotein research. The evidence of triacylated lipoproteins in mycobacteria AZD5582 nmr refuted the long held assumption, that N-acylation is restricted to Gram-negative bacteria. Thus, the acylation with three fatty acids is a common feature of mycobacterial and E. coli lipoproteins. But, mycobacterial lipoproteins differ from E. coli lipoproteins with respect to the fatty acids used for the triacylation. Mycobacteria-specific LY294002 fatty acid 10-methyl octadecanoic acid (tuberculostearic acid) is uniquely found in lipoproteins of M.
smegmatis[12, 13]. All three enzymes of the lipoprotein biosynthesis pathway, Lgt, LspA and Lnt are essential in Gram-negative, but not in Gram-positive bacteria. However, in M. tuberculosis, lgt, the first enzyme of the lipoprotein biosynthesis pathway is essential. A targeted deletion of lgt was not possible . In contrast, an lspA deletion mutant was viable, but the mutant strain showed a reduced number of CFU in an animal model and induced hardly any lung pathology. This confirmed a role of the lipoprotein biosynthesis pathway in pathogenesis of M. tuberculosis[23, 24]. Lipoproteins itself are well known virulence factors in pathogenic bacteria. M. tuberculosis lipoproteins in particular have been shown to suppress innate immune responses by TLR2 agonist activity .