posted on 2016-02-21, 12:48authored byPauline Krijgsheld, A. F.
Maarten Altelaar, Harm Post, Jeffrey
H. Ringrose, Wally H. Müller, Albert J. R. Heck, Han A. B. Wösten
Aspergillus niger is an important cell
factory
for the industrial production of enzymes. These enzymes are released
into the culture medium, from which they can be easily isolated. Here,
we determined with stable isotope dimethyl labeling the secretome
of five concentric zones of 7-day-old xylose-grown colonies of A. niger that had either or not been treated with cycloheximide.
As expected, cycloheximide blocked secretion of proteins at the periphery
of the colony. Unexpectedly, protein release was increased by cycloheximide
in the intermediate and central zones of the mycelium when compared
to nontreated colonies. Electron microscopy indicated that this is
due to partial degradation of the cell wall. In total, 124 proteins
were identified in cycloheximide-treated colonies, of which 19 secreted
proteins had not been identified before. Within the pool of 124 proteins,
53 secreted proteins were absent in nontreated colonies, and additionally,
35 proteins were released ≥4-fold in the central and subperipheral
zones of cycloheximide-treated colonies when compared to nontreated
colonies. The composition of the secretome in each of the five concentric
zones differed. This study thus describes spatial release of proteins
in A. niger, which is instrumental in understanding
how fungi degrade complex substrates in nature.