Journal of Bacteriology, November 1998, p. 5591-5600, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Center for Microbial Pathogenesis and Department of Microbiology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214
Received 17 April 1998/Accepted 26 August 1998
The chiA gene of Vibrio cholerae encodes a
polypeptide which degrades chitin, a homopolymer of
N-acetylglucosamine (GlcNAc) found in cell walls of
fungi and in the integuments of insects and crustaceans.
chiA has a coding capacity corresponding to a polypeptide
of 846 amino acids having a predicted molecular mass of 88.7 kDa. A
52-bp region with promoter activity was found immediately upstream of
the chiA open reading frame. Insertional inactivation of
the chromosomal copy of the gene confirmed that expression of chitinase
activity by V. cholerae required chiA.
Fluorescent analogues were used to demonstrate that the enzymatic
activity of ChiA was specific for
,1-4 glycosidic bonds located
between GlcNAc monomers in chitin. Antibodies against ChiA were
obtained by immunization of a rabbit with a MalE-ChiA hybrid protein.
Polypeptides with antigenic similarity to ChiA were expressed by
classical and El Tor biotypes of V. cholerae and by the
closely related bacterium Aeromonas hydrophila.
Immunoblotting experiments using the wild-type strain 569B and the
secretion mutant M14 confirmed that ChiA is an extracellular protein
which is secreted by the eps system. The eps
system is also responsible for secreting cholera toxin, an oligomeric
protein with no amino acid homology to ChiA. These results indicate
that ChiA and cholera toxin have functionally similar extracellular
transport signals that are essential for eps-dependent
secretion.
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