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Applied and Environmental Microbiology, March 2009, p. 1355-1362, Vol. 75, No. 5
0099-2240/09/$08.00+0     doi:10.1128/AEM.02141-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Unique Branching Patterns of Deinococcus Glycogen Branching Enzymes Are Determined by Their N-Terminal Domains{triangledown}

M. Palomo, S. Kralj,{dagger} M. J. E. C. van der Maarel,* and L. Dijkhuizen

Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands

Received 16 September 2008/ Accepted 27 December 2008

Glycogen branching enzymes (GBE) or 1,4-{alpha}-glucan branching enzymes (EC 2.4.1.18) introduce {alpha}-1,6 branching points in {alpha}-glucans, e.g., glycogen. To identify structural features in GBEs that determine their branching pattern specificity, the Deinococcus geothermalis and Deinococcus radiodurans GBE (GBEDg and GBEDr, respectively) were characterized. Compared to other GBEs described to date, these Deinococcus GBEs display unique branching patterns, both transferring relatively short side chains. In spite of their high amino acid sequence similarity (88%) the D. geothermalis enzyme had highest activity on amylose while the D. radiodurans enzyme preferred amylopectin. The side chain distributions of the products were clearly different: GBEDg transferred a larger number of smaller side chains; specifically, DP5 chains corresponded to 10% of the total amount of transferred chains, versus 6.5% for GBEDr. GH13-type GBEs are composed of a central (β/{alpha}) barrel catalytic domain and an N-terminal and a C-terminal domain. Characterization of hybrid Deinococcus GBEs revealed that the N2 modules of the N domains largely determined substrate specificity and the product branching pattern. The N2 module has recently been annotated as a carbohydrate binding module (CBM48). It appears likely that the distance between the sugar binding subsites in the active site and the CBM48 subdomain determines the average lengths of side chains transferred.

* Corresponding author. Mailing address: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands. Phone: 31 50 3632150. Fax: 31 50 3632154. E-mail: m.j.e.c.van.der.maarel{at}rug.nl

{triangledown} Published ahead of print on 9 January 2009.

{dagger} Present address: Genencor International B.V., Archimedesweg 30, 2333 CN Leiden, The Netherlands.

Applied and Environmental Microbiology, March 2009, p. 1355-1362, Vol. 75, No. 5
0099-2240/09/$08.00+0     doi:10.1128/AEM.02141-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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