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Applied and Environmental Microbiology, September 1998, p. 3202-3208, Vol. 64, No. 9
Institute for Biochemical Technology and
Microbiology, Technische Universität Wien, A-1060 Vienna,
Austria,1 and
CAYLA, 31400 Toulouse,
France2
Received 2 February 1998/Accepted 14 June 1998
Cell extracts of Trichoderma reesei exhibited dibasic
endopeptidase activity toward the carboxylic side of KR, RR, and PR sequences. This activity was stimulated by the presence of
Ca2+ ions and localized in vesicles of low bouyant density;
it therefore exhibited some similarity to yeast Kex2. Analytical
chromatofocusing revealed a single peak of activity. The dibasic
endopeptidase activity was strongly and irreversibly inhibited in vitro
as well as in vivo by 1 mM p-amidinophenylmethylsulfonyl
fluoride (pAPMSF) but not by PMSF at concentrations up to 5 mM. We
therefore used pAPMSF to study the role of the dibasic endopeptidase in
the secretion of protein by T. reesei. Secretion of
xylanase I (proprotein processing sequence -R-R-
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Role of Endoproteolytic Dibasic Proprotein
Processing in Maturation of Secretory Proteins in
Trichoderma reesei
-R-
-A-) and
xylanase II (-K-R-
-Q-) was strongly inhibited by 1 mM pAPMSF, and a
larger, unprocessed enzyme form was detected intracellularly under
these conditions. Secretion of cellobiohydrolase II (CBH II;
-E-R-
-Q-) was only slightly inhibited by pAPMSF, and no accumulation
of unprocessed precursors was detected. In contrast, secretion of CBH I
(-R-A-
-Q-) was stimulated by pAPMSF addition, and a simultaneous
decrease in the concentration of intracellular CBH I was detected.
Similar experiments were also carried out with a single heterologous
protein, ShBLE, the phleomycin-binding protein from
Streptoalloteichus hindustanus, fused to a series of model
proprotein-processing sequences downstream of the expression signals of
the Aspergillus nidulans gpdA promoter. Consistent with the
results obtained with homologous proteins, pAPMSF inhibited the
secretion of ShBLE with fusions containing dibasic (RK and KR) target
sequences, but it even stimulated secretion in fusions to LR, NHA, and
EHA target sequences. Addition of 5 mM PMSF, a nonspecific inhibitor of
serine protease, nonspecifically inhibited the secretion of
heterologous proteins from fusions bearing the NHA and LR targets.
These data point to the existence of different endoproteolytic
proprotein processing enzymes in T. reesei and demonstrate
that dibasic processing is obligatory for the secretion of the
proproteins containing this target.
*
Corresponding author. Mailing address: Institute for
Biochemical Technology and Microbiology, Technische Universität
Wien, Getreidemarkt 9/172.5, A-1060 Vienna, Austria. Phone:
43-1-58801-4707. Fax: 43-1-581-62-66. E-mail:
ckubicek{at}fbch.tuwien.ac.at.
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