| 简介 |
Pseudomonas aeruginosa is a Gram negative bacterium that uses polar type IV pili to adhere to and rapidly colonize surfaces. Within the P. aeruginosa species, there are five distinct alleles of the structural subunit, PilA, varying in amino acid sequence, association with specific accessory genes and presence of post- translational modifications. Group IV pilins from strain Pa5196 continued to be modified in a lipopolysaccharide mutant of Pa5196, demonstrating that, unlik e group I strains, the pilins of group IV are not modified with O-antigen units. Usi ng a combination of mass spectrometry and NMR spectroscopy, the pilin glycan was determined to be a linear oligosaccharide of five to eight alpha-1, 5-linked D- arabinofuranose (D-Araf) residues, covalently O-linked to the pilin via Thr. This sugar is rare in prokaryotes, occurring mainly in the unusual cell walls of mycobacteria, including the important human pathogens Mycobacterium tuberculosis, M. leprae and M. avium-intracellulare complex, where alpha-1, 5 - linked D-Araf chains link mycolic acids to peptidoglycan. Due in part to the technical challenges of working with slow-growing, pathogenic mycobacteria and extracting complex cell wall components for analysis, biosynthesis of D-Araf containing -- polymers is poorly defined. Wepropose that P. aeruginosa Pa5196, a rapid-growing and genetically tractable strain of low virulence that expresses copious glycosylated pili on its surface, represents an excellent model system for elucidation of the pathways for biosynthesis of D-Araf and its polymerization into mycobacteria l- like .alpha.1, 5 linked oligomers. Identification of the enzymes catalyzing these steps could provide novel targets for development of new anti-mycobacterial drugs. |
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