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Eukaryotic Cell, July 2007, p. 1178-1188, Vol. 6, No. 7
1535-9778/07/$08.00+0     doi:10.1128/EC.00354-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Two Novel, Putatively Cell Wall-Associated and Glycosylphosphatidylinositol-Anchored {alpha}-Glucanotransferase Enzymes of Aspergillus niger{triangledown}

R. M. van der Kaaij,1,2 X.-L. Yuan,3 A. Franken,3 A. F. J. Ram,3 P. J. Punt,4 M. J. E. C. van der Maarel,1,2,4* and L. Dijkhuizen1,2

Centre for Carbohydrate Bioprocessing, TNO-University of Groningen, Haren, The Netherlands,1 Microbial Physiology Research Group, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands,2 Fungal Genetics Research Group, Institute of Biology, Leiden University, Leiden, The Netherlands,3 Business Unit Food and Biotechnology Innovations, TNO Quality of Life, Zeist, The Netherlands4

Received 10 November 2006/ Accepted 25 April 2007

In the genome sequence of Aspergillus niger CBS 513.88, three genes were identified with high similarity to fungal {alpha}-amylases. The protein sequences derived from these genes were different in two ways from all described fungal {alpha}-amylases: they were predicted to be glycosylphosphatidylinositol anchored, and some highly conserved amino acids of enzymes in the {alpha}-amylase family were absent. We expressed two of these enzymes in a suitable A. niger strain and characterized the purified proteins. Both enzymes showed transglycosylation activity on donor substrates with {alpha}-(1,4)-glycosidic bonds and at least five anhydroglucose units. The enzymes, designated AgtA and AgtB, produced new {alpha}-(1,4)-glycosidic bonds and therefore belong to the group of the 4-{alpha}-glucanotransferases (EC 2.4.1.25 [EC] ). Their reaction products reached a degree of polymerization of at least 30. Maltose and larger maltooligosaccharides were the most efficient acceptor substrates, although AgtA also used small nigerooligosaccharides containing {alpha}-(1,3)-glycosidic bonds as acceptor substrate. An agtA knockout of A. niger showed an increased susceptibility towards the cell wall-disrupting compound calcofluor white, indicating a cell wall integrity defect in this strain. Homologues of AgtA and AgtB are present in other fungal species with {alpha}-glucans in their cell walls, but not in yeast species lacking cell wall {alpha}-glucan. Possible roles for these enzymes in the synthesis and/or maintenance of the fungal cell wall are discussed.

* Corresponding author. Mailing address: Centre for Carbohydrate Bioprocessing, TNO-University of Groningen, P.O. Box 14, 9750 AA 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 11 May 2007.

Eukaryotic Cell, July 2007, p. 1178-1188, Vol. 6, No. 7
1535-9778/07/$08.00+0     doi:10.1128/EC.00354-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Kelly, R. M., Leemhuis, H., Gatjen, L., Dijkhuizen, L. (2008). Evolution toward Small Molecule Inhibitor Resistance Affects Native Enzyme Function and Stability, Generating Acarbose-insensitive Cyclodextrin Glucanotransferase Variants. J. Biol. Chem. 283: 10727-10734 [Abstract] [Full Text]  
  • van der Kaaij, R. M., Janecek, S., van der Maarel, M. J. E. C., Dijkhuizen, L. (2007). Phylogenetic and biochemical characterization of a novel cluster of intracellular fungal {alpha}-amylase enzymes. Microbiology 153: 4003-4015 [Abstract] [Full Text]  


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