Genomics and Applied Biology 2018, Vol.9, No.5, 24-31
25
found indicated that
TrkH
and
TrkG
could independently provide higher K
+
transport capacity for organisms,
which were related to the regulation of
TrkA
, that is, the system showed dependence on
TrkA
(Epstein et al., 2003;
Su et al., 2008; Feng et al., 2009; Herrera et al., 2014). Two
Trk
gene family members,
Va-TrkA
and
Va-TrkH
, were
also found in
Vibrio alginolyticus
. When the two
Trk
gene family members were expressed in
E. coli
△
trkA
and
△
trkH
△
trkG
mutants, the mutants could resume growth in low K
+
conditions (Nakamura et al., 1998a; 1998b).
In addition, studies on fungal
Trk
systems have shown that most fungi contain at least one or two
Trk
family
potassium transporters, such as
Saccharomyces cerevisiae
(Ariño et al., 2010; Bagriantsev et al., 2013; Herrera et
al., 2014),
Schizosaccharomyces pombe
(Ariño et al., 2010),
Kluyveromyces lactis
(Prista et al., 2007),
Ruthenium
(Miranda et al., 2003),
Cylindrotheca
(Stříbný et al., 2012),
Candida albicans
(Rivetta et al., 2013) and so on.
Sc-Trk1
is
the first member of the
Trk
gene family found in fungi, which was from
Saccharomyces cerevisiae
.
Sc-Trk1
acts as a potassium transfer protein in the plasma membrane (Rodríguez-Navarro et al., 1984; Ramos et
al., 1985). The study found that
trkl
-deficient strains of
Saccharomyces cerevisiae
still maintained a relatively low
level of K
+
uptake activity indicating that other members of the
TRK
gene family exist in
Saccharomyces
cerevisiae
. Subsequent studies have found that
ScTrk2
is also a potassium transporter and both play an important
role in maintaining potassium balance in
Saccharomyces cerevisiae
(Chen et al., 2004; Alkhuder et al., 2010). It
can be seen that there are
TRK
gene families in both prokaryotic and eukaryotic microorganisms to maintain
osmotic balance in the organism.
Aspergillus niger
is an important industrial fermentation microorganism and one of the edible safety strain
identified by the US Food and Drug Administration. Furthermore, it is widely used in organic acids and industrial
enzyme preparations.
Aspergillus niger
is always found in complex environment, such as food, plant products and
soils, resulting to its salt and acid resistance. The regulation of osmotic pressure plays a crucial role in both high
salt and low pH environments, but the genes and mechanisms associated with osmoregulation in
Aspergillus niger
have been rarely reported. In this study, bioinformatics methods were used to identify the entire
Trk
family
members in
Aspergillus niger
, which provided the basis for the cloning of members of the
TRK
gene family
.
The
analysis of their evolution, structure and protein interaction networks was of great significance for further study of
their function and the osmotic regulation mechanism of
Aspergillus niger
.
1 Results
1.1 Identification of
Aspergillus niger
gene family members
Four
TRK
gene family members were identified in the
Aspergillus niger
genome, including
AnTrk1
(Accession
number: EHA26772),
AnTrk2
(NM_001181562),
AnTrk3
(EHA26772) and
AnTrk4
(NM_001181562). The
encoded protein sequences are smaller than the
Trk
genes in yeast and the length of amino acid ranges from 617 to
826. The molecular weight ranges from 67.87 kD to 90.86 kD. Analysis of the domains revealed that the four
members of the
TRK
gene family in
Aspergillus niger
and yeast were all contained a
TrkH
functional domain, but
the size of the domains was different among the family. The
TrkH
functional domain is associated with cation
transport. Therefore, it can be inferred from the above results that
AnTrk1
,
AnTrk2
,
AnTrk3
and
AnTrk4
are four
members of the TRK gene family in
Aspergillus niger
(Table 1).
Table 1 The characteristics of identified TRK gene family in
Aspergillus niger
Gene
Gene accession
Protein length
Molecular mass( kD)
Functional domain
AnTrk1
EHA21096
826
90.86
111501
AnTrk2
EHA21450
701
77.11
128497
AnTrk3
EHA26772
617
67.87
189500
AnTrk4
EHA26877
681
74.91
118499
Trk1
NM_001181562
1235
135.85
2502
Trk2
NM_001179840
889
97.79
2501
1.2
Aspergillus niger TRK
genes and yeast
TRK
genes alignment da/ds calculation
The evolutionary selection pressure is often expressed as da/ds. To analyze the evolutionary pressure of the
TRK
gene family in
Aspergillus niger
, the gene sequences and mRNA sequences of
AnTrk1
,
AnTrk2
,
AnTrk3
, and
