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Applied and Environmental Microbiology, June 2003, p. 3119-3128, Vol. 69, No. 6
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.6.3119-3128.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Growth of Hyperthermophilic Archaeon Pyrococcus furiosus on Chitin Involves Two Family 18 Chitinases
Jun Gao, Michael W. Bauer,
Keith R. Shockley, Marybeth A. Pysz, and Robert M. Kelly*
Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905
Received 10 September 2002/
Accepted 11 March 2003
Pyrococcus furiosus was found to grow on chitin, adding this polysacharide to the inventory of carbohydrates utilized by this hyperthermophilic archaeon. Accordingly, two open reading frames (chiA [Pf1234] and chiB [Pf1233]) were identified in the genome of P. furiosus, which encodes chitinases with sequence similarity to proteins from the glycosyl hydrolase family 18 in less-thermophilic organisms. Both enzymes contain multiple domains that consist of at least one binding domain and one catalytic domain. ChiA (ca. 39 kDa) contains a putative signal peptide, as well as a binding domain (ChiABD), that is related to binding domains associated with several previously studied bacterial chitinases. chiB, separated by 37 nucleotides from chiA and in the same orientation, encodes a polypeptide with two different proline-threonine-rich linker regions (6 and 3 kDa) flanking a chitin-binding domain (ChiBBD [11 kDa]), followed by a catalytic domain (ChiBcat [35 kDa]). No apparent signal peptide is encoded within chiB. The two chitinases share little sequence homology to each other, except in the catalytic region, where both have the catalytic glutamic acid residue that is conserved in all family 18 bacterial chitinases. The genes encoding ChiA, without its signal peptide, and ChiB were cloned and expressed in Escherichia coli. ChiA exhibited no detectable activity toward chitooligomers smaller than chitotetraose, indicating that the enzyme is an endochitinase. Kinetic studies showed that ChiB followed Michaelis-Menten kinetics toward chitotriose, although substrate inhibition was observed for larger chitooligomers. Hydrolysis patterns on chitooligosaccharides indicated that ChiB is a chitobiosidase, processively cleaving off chitobiose from the nonreducing end of chitin or other chitooligomers. Synergistic activity was noted for the two chitinases on colloidal chitin, indicating that these two enzymes work together to recruit chitin-based substrates for P. furiosus growth. This was supported by the observed growth on chitin as the sole carbohydrate source in sulfur-free media.
* Corresponding author. Mailing address: Department of Chemical Engineering, North Carolina State University, Stinson Dr., Box 7905, Raleigh, NC 27695-7905. Phone: (919) 515-6396. Fax: (919) 515-3465. E-mail:
rmkelly{at}eos.ncsu.edu.
Present address: Syngenta Biotechnology, Inc., Research Triangle Park, NC 27709.
Applied and Environmental Microbiology, June 2003, p. 3119-3128, Vol. 69, No. 6
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.6.3119-3128.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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