Mammalian chitinase, a chitinolytic enzyme expressed by macrophages, has be
en detected in atherosclerotic plaques and is elevated in blood and tissues
of guinea pigs infected with Aspergillus, Its normal physiological functio
n is unknown, To understand how the enzyme interacts with its substrate, we
have characterized the chitin-binding domain, The C-terminal 49 amino acid
s make up the minimal sequence required for chitin binding activity, The ab
sence of this domain does not affect the ability of the enzyme to hydrolyze
the soluble substrate, triacetylchitotriose, but abolishes hydrolysis of i
nsoluble chitin, Within the minimal chitin-binding domain are six cysteines
; mutation of any one of these to serine results in complete loss of chitin
binding activity. Analysis of purified recombinant chitin-binding domain r
evealed the presence of three disulfide linkages. The recombinant domain bi
nds specifically to chitin but does not bind chitosan, cellulose, xylan, be
ta-1,3-glucan, beta-1,3-1,4-glucan, or mannan, Fluorescently tagged chitin-
binding domain was used to demonstrate chitin-specific binding to Saccharom
yces cerevisiae, Candida albicans, Mucor rouxii, and Neurospora crassa, The
se experiments define structural features of the minimal domain of human ch
itinase required for both specifically binding to and hydrolyzing insoluble
chitin and demonstrate relevant binding within the context of the fungal c
ell wall.