Characterization of sulfhydryl oxidase from Aspergillus tubingensis
Abstract
Background: Despite of the presence of sulfhydryl oxidases (SOXs) in the secretomes of industrially relevant organisms
and their many potential applications, only few of these enzymes have been biochemically characterized. In addition,
basic functions of most of the SOX enzymes reported so far are not fully understood. In particular, the physiological
role of secreted fungal SOXs is unclear.
Results: The recently identified SOX from Aspergillus tubingensis (AtSOX) was produced, purified and characterized in
the present work. AtSOX had a pH optimum of 6.5, and showed a good pH stability retaining more than 80% of the
initial activity in a pH range 4-8.5 within 20 h. More than 70% of the initial activity was retained after incubation at 50 °C
for 20 h. AtSOX contains a non-covalently bound flavin cofactor. The enzyme oxidised a sulfhydryl group of glutathione
to form a disulfide bond, as verified by nuclear magnetic resonance spectroscopy. AtSOX preferred glutathione as
a substrate over cysteine and dithiothreitol. The activity of the enzyme was totally inhibited by 10 mM zinc sulphate.
Peptide- and protein-bound sulfhydryl groups in bikunin, gliotoxin, holomycin, insulin B chain, and ribonuclease A,
were not oxidised by the enzyme. Based on the analysis of 33 fungal genomes, SOX enzyme encoding genes were
found close to nonribosomal peptide synthetases (NRPS) but not with polyketide synthases (PKS). In the phylogenetic
tree, constructed from 25 SOX and thioredoxin reductase sequences from IPR000103 InterPro family, AtSOX
was evolutionary closely related to other Aspergillus SOXs. Oxidoreductases involved in the maturation of
nonribosomal peptides of fungal and bacterial origin, namely GliT, HlmI and DepH, were also evolutionary
closely related to AtSOX whereas fungal thioreductases were more distant.
Conclusions: AtSOX (55 kDa) is a fungal secreted flavin-dependent enzyme with good stability to both pH
and temperature. A Michaelis-Menten behaviour was observed with reduced glutathione as a substrate. Based
on the location of SOX enzyme encoding genes close to NRPSs, SOXs could be involved in the secondary
metabolism and act as an accessory enzyme in the production of nonribosomal peptides.
Main Authors
Format
Articles
Research article
Published
2017
Series
Subjects
Publication in research information system
Publisher
BioMed Central
The permanent address of the publication
https://urn.fi/URN:NBN:fi:jyu-201712114613Use this for linking
Review status
Peer reviewed
ISSN
1471-2091
DOI
https://doi.org/10.1186/s12858-017-0090-4
Language
English
Published in
BMC Biochemistry
Citation
- Nivala, O., Faccio, G., Arvas, M., Permi, P., Buchert, J., Kruus, K., & Mattinen, M.-L. (2017). Characterization of sulfhydryl oxidase from Aspergillus tubingensis. BMC Biochemistry, 18, Article 15. https://doi.org/10.1186/s12858-017-0090-4
Copyright© The Author(s) 2017. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0
International License.