Eukaryotic Cell doi:10.1128/EC.00354-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Characterization of two novel, putatively cell wall associated and GPI-anchored, 
- glucanotransferase enzymes of Aspergillus niger
R. M. van der Kaaij,
X-L. Yuan,
A. Franken,
A. F.J. Ram,
P. J. Punt,
M. J.E.C. van der Maarel*,
and
L. Dijkhuizen
Centre for Carbohydrate Bioprocessing, TNO-University of Groningen, Haren, The Netherlands; Microbial Physiology Research Group, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, The Netherlands; Fungal Genetics Research Group, Institute of Biology, Leiden University, Leiden, The Netherlands; Business Unit Food and Biotechnology Innovations, TNO Quality of Life, Zeist and Groningen, The Netherlands
* To whom correspondence should be addressed. Email:
m.j.e.c.van.der.maarel{at}rug.nl.
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Abstract |
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In the genome sequence of Aspergillus niger CBS 513.88 three genes were identified with high similarity to fungal 
-amylases. The derived protein sequences were in two ways aberrant from all described fungal -amylases: they were predicted to be glycosylphosphatidylinositol-anchored, and some highly conserved amino acids of the -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 -(1,4)-glycosidic bonds and at least five anhydroglucose units. The enzymes, designated AgtA and AgtB, produced new -(1,4)-glycosidic bonds and therefore belong to the group of the 4--glucanotransferases (EC 2.4.1.25). 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 -(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 -glucans in their cell walls, but not in yeast species lacking cell wall -glucan. The possible role for these enzymes in the synthesis and/or maintenance of the fungal cell wall is discussed.
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