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Figure 3 | BMC Genomics

Figure 3

From: The genome sequence of the fish pathogen Aliivibrio salmonicida strain LFI1238 shows extensive evidence of gene decay

Figure 3

Key steps in the chitinolytic cascade. Functional assignment of A. salmonicida CDSs are derived from bioinformatical analysis, and the abbreviated gene IDs are indicated at each step. Putative non-functional A. salmonicida products are boxed. Initially, a methyl chemotaxis protein (VSAL_II0134) and a chitin binding protein (VSAL_I2601) are involved in sensing and attachment to chitin respectively. Extracellular chitinases (VSAL_I0763/I0902, VSAL_I1414, VSAL_I1942, VSAL_I0757 and VSAL_II0217) partly break down chitin. Chitin oligomers (GlcNAc)n are translocated across the outer membrane by chitoporin (VSAL_I2352), while the transport of monomers and dimers (GlcNAc)1,2 is mediated by unspecific porins. In the periplasm, the chitin oligomers are further degraded to yield (GlcNAc)1,2 by chitodextrinase (VSAL_I1108), N-acetylglucosamidase (VSAL_I2583 and VSAL_II0052) and N-acetylhexosamidase (VSAL_II0575). (GlcNAc)1 are transported across the inner membrane by a permease (VSAL_I0831), while the transport of (GlcNAc)2 are mediated by an ABC-transporter (VSAL_I2577- I2580). Deacetylated monomers (GlcN) are transported into the cytosol by a PTS transporter (VSAL_I0703- I0708). Cytoplasmic enzymes (VSAL_I2581- I2582, VSAL_I2584- I2585, VSAL_I0830 and VSAL_I2812) convert the transport products into fructose-6-P, acetate and ammonia. In the absence of chitin, the perisplasmic chitin oligosaccharide binding protein CBP (VSAL_I2576) binds to the chitin sensor/kinase ChiS (VSAL_I2575) and represses transcription of chitinolytic genes. In presence of chitin, the complex dissociates as CBP binds to the chitin polysaccharides and chitinolytic genes are expressed.

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