Flavobacterium johnsoniae Chitinase ChiA Is Required for Chitin Utilization and Is Secreted by the Type IX Secretion System

Kharade, Sampada S.; McBride, Mark J.

doi:10.1128/jb.01170-13

Cited by 98 publications

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“…Eleven other F. johnsoniae proteins have TIGR04131-type CTDs, as do numerous proteins from other species belonging to the phylum Bacteroidetes that have T9SSs. We have speculated that these TIGR04131-type CTDs target proteins for secretion by the T9SS (7,8), but with the exception of SprB, T9SS-mediated secretion of these proteins has not been experimentally demonstrated in any organism.Proteins required for secretion by the F. johnsoniae T9SS include GldK, GldL, GldM, and GldN or its paralog GldO (6,11). SprA, SprE, and SprT also have important roles in T9SS-mediated secretion, and cells with mutations in the genes encoding these proteins are severely but incompletely deficient in secretion (5, 6, 18).…”

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“…Motility proteins are not the only cargo for the F. johnsoniae T9SS. It is also required for secretion of the soluble extracellular chitinase ChiA (7), and 51 other F. johnsoniae proteins are predicted to use this secretion system (6). Many proteins secreted by T9SSs are very large.…”

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“…The CTDs are necessary and sufficient for secretion by the T9SS. P. gingivalis HBP35 and F. johnsoniae ChiA lacking their CTDs are not secreted, and heterologous fusion proteins carrying the HBP35 and ChiA CTDs are efficiently secreted (7,17). Many T9SS CTDs of F. johnsoniae and P. gingivalis belong to TIGRFAM protein domain family TIGR04183 (6, 8, 14).…”

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“…Proteins secreted by T9SSs have cleavable N-terminal signal peptides and are apparently exported across the cytoplasmic membrane via the Sec system (9, 14). They also have conserved carboxy-terminal domains (CTDs) of approximately 60 to 100 amino acids that target them for secretion across the outer membrane by the T9SS (6,7,9,14,15). The CTDs appear to be proteolytically cleaved during or after secretion across the outer membrane (9, 16).…”

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Flavobacterium johnsoniae PorV Is Required for Secretion of a Subset of Proteins Targeted to the Type IX Secretion System

Kharade

McBride

2015

J Bacteriol

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Flavobacterium johnsoniae exhibits gliding motility and digests many polysaccharides, including chitin. A novel protein secretion system, the type IX secretion system (T9SS), is required for gliding and chitin utilization. The T9SS secretes the cell surface motility adhesins SprB and RemA and the chitinase ChiA. Proteins involved in secretion by the T9SS include GldK, GldL, GldM, GldN, SprA, SprE, and SprT. Porphyromonas gingivalis has orthologs for each of these that are required for secretion of gingipain protease virulence factors by its T9SS. P. gingivalis porU and porV have also been linked to T9SS-mediated secretion, and F. johnsoniae has orthologs of these. Mutations in F. johnsoniae porU and porV were constructed to determine if they function in secretion. Cells of a porV deletion mutant were deficient in chitin utilization and failed to secrete ChiA. They were also deficient in secretion of the motility adhesin RemA but retained the ability to secrete SprB. SprB is involved in gliding motility and is needed for formation of spreading colonies on agar, and the porV mutant exhibited gliding motility and formed spreading colonies. However, the porV mutant was partially deficient in attachment to glass, apparently because of the absence of RemA and other adhesins on the cell surface. The porV mutant also appeared to be deficient in secretion of numerous other proteins that have carboxy-terminal domains associated with targeting to the T9SS. PorU was not required for secretion of ChiA, RemA, or SprB, indicating that it does not play an essential role in the F. johnsoniae T9SS.C ells of Flavobacterium johnsoniae, and of many members of the phylum Bacteroidetes, crawl rapidly over surfaces by a process known as gliding motility (1). F. johnsoniae gliding involves the rapid movement of the adhesins SprB and RemA along the cell surface (2-4). These proteins are secreted across the outer membrane by a novel protein secretion system originally called the Por secretion system and more recently referred to as the type IX secretion system (T9SS) (5, 6). Motility proteins are not the only cargo for the F. johnsoniae T9SS. It is also required for secretion of the soluble extracellular chitinase ChiA (7), and 51 other F. johnsoniae proteins are predicted to use this secretion system (6). Many proteins secreted by T9SSs are very large. ChiA, RemA, and SprB, for example, are 166, 152, and 669 kDa, respectively (3, 4, 7). The mechanism that allows efficient secretion of such large proteins by the T9SS is not known. T9SSs are found in many members of the phylum Bacteroidetes, and they are apparently limited to this phylum (8, 9). The proteins required for T9SS-mediated secretion are not similar in sequence to proteins of other bacterial secretion systems (5,8,10). Although the T9SS was only recently discovered, it has already been associated with motility (11), virulence (5), chitin and cellulose digestion (7, 12), and colonization of and protection of plants from pathogens (13).T9SSs were originally identified in F. johnso...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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