Affiliation:
1. Molecular Genetics of Industrial Microorganisms, Wageningen Agricultural University, NL-6703 HA Wageningen, The Netherlands
Abstract
ABSTRACT
A gene encoding a third α-galactosidase (AglB) from
Aspergillus niger
has been cloned and sequenced. The gene consists of an open reading frame of 1,750 bp containing six introns. The gene encodes a protein of 443 amino acids which contains a eukaryotic signal sequence of 16 amino acids and seven putative N-glycosylation sites. The mature protein has a calculated molecular mass of 48,835 Da and a predicted pI of 4.6. An alignment of the AglB amino acid sequence with those of other α-galactosidases revealed that it belongs to a subfamily of α-galactosidases that also includes
A. niger
AglA.
A. niger
AglC belongs to a different subfamily that consists mainly of prokaryotic α-galactosidases. The expression of
aglA
,
aglB
,
aglC
, and
lacA
, the latter of which encodes an
A. niger
β-galactosidase, has been studied by using a number of monomeric, oligomeric, and polymeric compounds as growth substrates. Expression of
aglA
is only detected on galactose and galactose-containing oligomers and polymers. The
aglB
gene is expressed on all of the carbon sources tested, including glucose. Elevated expression was observed on xylan, which could be assigned to regulation via XlnR, the xylanolytic transcriptional activator. Expression of
aglC
was only observed on glucose, fructose, and combinations of glucose with xylose and galactose. High expression of
lacA
was detected on arabinose, xylose, xylan, and pectin. Similar to
aglB
, the expression on xylose and xylan can be assigned to regulation via XlnR. All four genes have distinct expression patterns which seem to mirror the natural substrates of the encoded proteins.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
88 articles.
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