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Journal of Bacteriology, January 1999, p. 284-290, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
An Endoglucanase, EglA, from the Hyperthermophilic Archaeon
Pyrococcus furiosus Hydrolyzes
-1,4 Bonds in
Mixed-Linkage (1
3),(1
4)-
-D-Glucans and
Cellulose
Michael W.
Bauer,1,
Lance E.
Driskill,1
Walter
Callen,2
Marjory A.
Snead,2
Eric J.
Mathur,2 and
Robert M.
Kelly1,*
Department of Chemical Engineering, North
Carolina State University, Raleigh, North Carolina
27695,1 and
Diversa Corporation, San
Diego, California 921212
Received 19 June 1998/Accepted 19 October 1998
The eglA gene, encoding a thermostable endoglucanase
from the hyperthermophilic archaeon Pyrococcus furiosus,
was cloned and expressed in Escherichia coli. The
nucleotide sequence of the gene predicts a 319-amino-acid protein with
a calculated molecular mass of 35.9 kDa. The endoglucanase has a
19-amino-acid signal peptide but not cellulose-binding domain. The
P. furiosus endoglucanase has significant amino acid
sequence similarities, including the conserved catalytic nucleophile
and proton donor, with endoglucanases from glucosyl hydrolase family
12. The purified recombinant enzyme hydrolyzed
-1,4 but not
-1,3
glucosidic linkages and had the highest specific activity on
cellopentaose (degree of polymerization [DP] = 5) and cellohexaose
(DP = 6) oligosaccharides. To a lesser extent, EglA also
hydrolyzed shorter cellodextrins (DP < 5) as well as the
amorphous portions of polysaccharides which contain only
-1,4 bonds
such as carboxymethyl cellulose, microcrystalline cellulose, Whatman
paper, and cotton linter. The highest specific activity toward
polysaccharides occurred with mixed-linkage
-glucans such as barley
-glucan and lichenan. Kinetics studies with cellooliogsaccharides and p-nitrophenyl-cellooligosaccharides indicated that the
enzyme had three glucose binding subsites (
I,
II, and
III) for
the nonreducing end and two glucose binding subsites (+I and +II) for
the reducing end from the scissile glycosidic linkage. The enzyme had
temperature and pH optima of 100°C and 6.0, respectively; a half-life
of 40 h at 95°C; and a denaturing temperature of 112°C as
determined by differential scanning calorimetry. The discovery of a
thermostable enzyme with this substrate specificity has implications for both the evolution of enzymes involved in polysaccharide hydrolysis and the occurrence of growth substrates in hydrothermal vent environments.
*
Corresponding author. Mailing address: North Carolina
State University, Department of Chemical Engineering, Box 7905, Raleigh, NC 27695-7905. Phone: (919) 515-6396. Fax: (919) 515-3465. E-mail: rmkelly{at}eos.ncsu.edu.

Present address: Novartis Agribusiness Research, Inc., Research
Triangle Park, NC
27709.
Journal of Bacteriology, January 1999, p. 284-290, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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