NDLI: Processivity, Substrate Binding, and Mechanism of Cellulose Hydrolysis by Thermobifida fusca Cel9A▿

Content Provider	PubMed Central
Author	Li, Yongchao Irwin, Diana C. Wilson, David B.
Copyright Year	2007
Abstract	Thermobifida fusca Cel9A-90 is a processive endoglucanase consisting of a family 9 catalytic domain (CD), a family 3c cellulose binding module (CBM3c), a fibronectin III-like domain, and a family 2 CBM. This enzyme has the highest activity of any individual T. fusca enzyme on crystalline substrates, particularly bacterial cellulose (BC). Mutations were introduced into the CD or the CBM3c of Cel9A-68 using site-directed mutagenesis. The mutant enzymes were expressed in Escherichia coli; purified; and tested for activity on four substrates, ligand binding, and processivity. The results show that H125 and Y206 play an important role in activity by forming a hydrogen bonding network with the catalytic base, D58; another important supporting residue, D55; and Glc(−1) O1. R378, a residue interacting with Glc(+1), plays an important role in processivity. Several enzymes with mutations in the subsites Glc(−2) to Glc(−4) had less than 15% activity on BC and markedly reduced processivity. Mutant enzymes with severalfold-higher activity on carboxymethyl cellulose (CMC) were found in the subsites from Glc(−2) to Glc(−4). The CBM3c mutant enzymes, Y520A, R557A/E559A, and R563A, had decreased activity on BC but had wild-type or improved processivity. Mutation of D513, a conserved residue at the end of the CBM, increased activity on crystalline cellulose. Previous work showed that deletion of the CBM3c abolished crystalline activity and processivity. This study shows that it is residues in the catalytic cleft that control processivity while the CBM3c is important for loose binding of the enzyme to the crystalline cellulose substrate.
Related Links	http://dx.doi.org/10.1128/aem.02960-06
Ending Page	3172
Page Count	8
Starting Page	3165
File Format	PDF
ISSN	00992240
e-ISSN	10985336
Journal	Applied and Environmental Microbiology
Issue Number	10
Volume Number	73
Language	English
Publisher	American Society for Microbiology
Publisher Date	2007-05-15
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Biotechnology Food Science Ecology Applied Microbiology and Biotechnology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Ecology Food Science Applied Microbiology and Biotechnology Biotechnology

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