and is performed by deneddylases such as the
COP9 signalosome (constitutive photomorphogenesis 9, CSN) (Beckmann et al. 2015). In most
fungi, plants or in humans, it is a highly conserved complex consisting of eight CSN subunits including an intrinsic JAMM motif with
Nedd8 isopeptidase activity in one subunit.
Neurospora crassa and S. pombe possess
seven- and six-subunit CSNs, respectively, and
in S. cerevisiae there is only the conserved
deneddylase subunit as part of an alternative
CSN complex. Dysfunction of CSN results in
lethality in plants or mammals but not in
fungi, which makes them an attractive model
organism to study CSN complex assembly and
the function of the different subunits (Braus
et al. 2010). CSN recognizes substrate free
CRLs (Lingaraju et al. 2014) and physically
interacts within the nucleus with a second
deneddylase Den1/A. This interaction is found
in A. nidulans as well as in human cells (Christmann et al. 2013; Schinke et al. 2016). Fungal
CSN is composed of an inactive seven-subunit
pre-complex, which incorporates the deneddylase subunit in a final step, resulting in a catalytically active complex (Beckmann et al. 2015).
In N. crassa, CSN mutant strains result in stabilization of the circadian clock regulator FRQ,
defects in light control (see Sect. II.A.2), and
impaired asexual development (Wang et al.
2010). Loss of any of the eight CSN subunits
of A. nidulans leads to impaired light control, a
block in sexual development and a brownish
colony with more than a hundred accumulated
secondary metabolites including orsellinic acid
derivatives (Busch et al. 2003, 2007; Nahlik et al.
2010).
COP9-mediated deneddylation of CulA
deactivates E3 SCF ubiquitin ligases and results
in disassembly. Cand1 (cullin associated Nedd8
dissociated 1) acts as Fbox receptor exchange
factor by blocking the neddylation site of CulA.
Multiple cycles of disassembly and assembly
ensure the appropriate exchange of different
Fbox proteins to degrade different target proteins in different environments or during development (Choo et al. 2011; Wu et al. 2013).
Cand1/A is encoded as single protein in higher
eukaryotes and fungi like N. crassa, Verticillium
dahliae, or the opportunistic pathogen C. albicans, whereas the A. nidulans gene has been
split into two separate genes, which encoded
proteins are interacting (Helmstaedt et al.
2011; Sela et al. 2012). Deletion of one or both
cand genes in A. nidulans leads to impaired
conidiospore and fruiting body formation and
to a similarly altered secondary metabolism
with a brownish colony color as for the defective CSN (Helmstaedt et al. 2011; Nahlik et al.
2010). The deneddylation of cullins, the dissociation of the SkpA adaptor/Fbox receptor
complex, the binding of the Cand protein, and
the following reactivation of the SCF complex
are highly dynamic processes that require tight
regulation (Liu et al. 2018).
Deubiquitinases (DUBs) are required for
the processing of ubiquitin precursors and for
the removal of ubiquitin molecules from target
proteins in order to generate the free ubiquitin
pool for E1 ubiquitin-activating enzymes
(Fig. 8.4). DUBs are classified into seven different families (Komander et al. 2009; Rehman
et al. 2016). (1) The JAMM domain metalloprotease DUBs, such as the Rpn11 (regulatory particle non-ATPase 11) of the proteasomal lid,
6
contain an MPN+ domain and are similar to the
deneddylase subunit of CSN (Meister et al.
2016). All other DUBs are cysteine proteases:
(2) ubiquitin C-terminal hydrolases (UCH); (3)
Machado-Joseph domain (Josephin-domain)
containing proteases (MJD), which are missing
in some yeasts (Hutchins et al. 2013); (4) ovarian tumor proteases (OTU); (5) ubiquitinspecific proteases (USP); (6) the motif interacting with Ub-containing novel DUB family
(MINDY) (Rehman et al. 2016); and (7) the
zinc finger with UFM1-specific peptidase
domain protein/C6orf113/ZUP1 (ZUFSP) family (Haahr et al. 2018).
The DUB distribution to the different
families is quite conserved between fungi and
humans with most members in the ubiquitinspecific proteases family with 17 USPs in S.
cerevisiae and more than 50 in humans (Hutchins et al. 2013). Any single deletion of the genes
for the 17 USP DUBs of S. cerevisiae is viable
6 lid ¼ removable or hinged cover of a container, here: the
cover of the proteasome core.
192
J. Gerke et al.
COP9 signalosome (constitutive photomorphogenesis 9, CSN) (Beckmann et al. 2015). In most
fungi, plants or in humans, it is a highly conserved complex consisting of eight CSN subunits including an intrinsic JAMM motif with
Nedd8 isopeptidase activity in one subunit.
Neurospora crassa and S. pombe possess
seven- and six-subunit CSNs, respectively, and
in S. cerevisiae there is only the conserved
deneddylase subunit as part of an alternative
CSN complex. Dysfunction of CSN results in
lethality in plants or mammals but not in
fungi, which makes them an attractive model
organism to study CSN complex assembly and
the function of the different subunits (Braus
et al. 2010). CSN recognizes substrate free
CRLs (Lingaraju et al. 2014) and physically
interacts within the nucleus with a second
deneddylase Den1/A. This interaction is found
in A. nidulans as well as in human cells (Christmann et al. 2013; Schinke et al. 2016). Fungal
CSN is composed of an inactive seven-subunit
pre-complex, which incorporates the deneddylase subunit in a final step, resulting in a catalytically active complex (Beckmann et al. 2015).
In N. crassa, CSN mutant strains result in stabilization of the circadian clock regulator FRQ,
defects in light control (see Sect. II.A.2), and
impaired asexual development (Wang et al.
2010). Loss of any of the eight CSN subunits
of A. nidulans leads to impaired light control, a
block in sexual development and a brownish
colony with more than a hundred accumulated
secondary metabolites including orsellinic acid
derivatives (Busch et al. 2003, 2007; Nahlik et al.
2010).
COP9-mediated deneddylation of CulA
deactivates E3 SCF ubiquitin ligases and results
in disassembly. Cand1 (cullin associated Nedd8
dissociated 1) acts as Fbox receptor exchange
factor by blocking the neddylation site of CulA.
Multiple cycles of disassembly and assembly
ensure the appropriate exchange of different
Fbox proteins to degrade different target proteins in different environments or during development (Choo et al. 2011; Wu et al. 2013).
Cand1/A is encoded as single protein in higher
eukaryotes and fungi like N. crassa, Verticillium
dahliae, or the opportunistic pathogen C. albicans, whereas the A. nidulans gene has been
split into two separate genes, which encoded
proteins are interacting (Helmstaedt et al.
2011; Sela et al. 2012). Deletion of one or both
cand genes in A. nidulans leads to impaired
conidiospore and fruiting body formation and
to a similarly altered secondary metabolism
with a brownish colony color as for the defective CSN (Helmstaedt et al. 2011; Nahlik et al.
2010). The deneddylation of cullins, the dissociation of the SkpA adaptor/Fbox receptor
complex, the binding of the Cand protein, and
the following reactivation of the SCF complex
are highly dynamic processes that require tight
regulation (Liu et al. 2018).
Deubiquitinases (DUBs) are required for
the processing of ubiquitin precursors and for
the removal of ubiquitin molecules from target
proteins in order to generate the free ubiquitin
pool for E1 ubiquitin-activating enzymes
(Fig. 8.4). DUBs are classified into seven different families (Komander et al. 2009; Rehman
et al. 2016). (1) The JAMM domain metalloprotease DUBs, such as the Rpn11 (regulatory particle non-ATPase 11) of the proteasomal lid,
6
contain an MPN+ domain and are similar to the
deneddylase subunit of CSN (Meister et al.
2016). All other DUBs are cysteine proteases:
(2) ubiquitin C-terminal hydrolases (UCH); (3)
Machado-Joseph domain (Josephin-domain)
containing proteases (MJD), which are missing
in some yeasts (Hutchins et al. 2013); (4) ovarian tumor proteases (OTU); (5) ubiquitinspecific proteases (USP); (6) the motif interacting with Ub-containing novel DUB family
(MINDY) (Rehman et al. 2016); and (7) the
zinc finger with UFM1-specific peptidase
domain protein/C6orf113/ZUP1 (ZUFSP) family (Haahr et al. 2018).
The DUB distribution to the different
families is quite conserved between fungi and
humans with most members in the ubiquitinspecific proteases family with 17 USPs in S.
cerevisiae and more than 50 in humans (Hutchins et al. 2013). Any single deletion of the genes
for the 17 USP DUBs of S. cerevisiae is viable
6 lid ¼ removable or hinged cover of a container, here: the
cover of the proteasome core.
192
J. Gerke et al.