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cj0757 , cj0758 and cj0759 , homologs to hrcA , grpE and dnaK that are
involved in the heat-shock response ( Parkhill et al., 2000 ). In addition, other
upregulated genes included cj0311 , encoding Ctc that is involved in general
stress response ( Volkert, Loewen, Switala, Crowley, & Conley, 1994 ), trxA
and trxB (encoding a thioredoxin and its reductase) with a role in oxidative
stress tolerance, and 9 genes from a group of 18 genes involved in iron
transport that show transcriptional changes under low iron conditions
( Holmes et al., 2005 ). Certainly, the effect of nitrosative stress in the
upregulation of iron acquisition has been demonstrated in a number of other
bacteria ( Hernandez-Urzua et al., 2007; Moore et al., 2004; Mukhopadhyay
et al., 2004; Richardson et al., 2006 ). The binding of NO to iron-bound
Fur maintains the de-repression of genes under control of this transcriptional
repressor.
Differences in the chemistry of S -nitrosothiols (SNOs) such as GSNO (a
nitrosative agent) and NOCs (NO donors) and their biological interactions
have been recently reviewed ( Bowman et al., 2011 ). Indeed, SNOs and their
derivative species play biologically relevant roles far beyond the simple
release of NO ( Hess et al., 2005 ). Due to the moderate stability of GSNO,
this compound is widely used in bacterial growth experiments, although for
the purpose of studying the biological effects of NO it is not ideal. For
instance, transfer of NO รพ from GSNO to membrane thiols is proposed
in Bacillus species ( Morris & Hansen, 1981 ), but other studies suggest that
toxicity is related to active transport: in E. coli , S -nitroso- L -cysteinylglycine,
an SNO-derived nitrosated dipeptide, is transported inwards (via the
Dpp-encoded dipeptide permease), resulting in intracellular transnitrosation
reactions ( Jarboe, Hyduke, Tran, Chou, & Liao, 2008; Laver et al., 2013 ).
Interestingly, comparison of the transcriptional responses of C. jejuni
exposed to GSNO ( Monk et al., 2008 ) or a combination of NOCs
(NOC-5 and NOC-7) shows common features. The Cgb and Ctb globins,
heat-shock proteins and regulators seem to be similarly affected by either
NO or GSNO ( Smith et al., 2011 ). In contrast, transcriptional responses
of E. coli in continuous culture in the presence of GSNO or NOCs revealed
some similarities but several important differences ( Pullan et al., 2007 ).
NO is released from GSNO under biological conditions ( Singh, Hogg,
Joseph, & Kalyanaraman, 1996 ), albeit at concentrations much lower than
the GSNO concentration: 500
MNO
( Jarboe et al., 2008 ). It is therefore possible that the transcriptional profile
of C. jejuni in the presence of GSNO is a direct result of NO release. Indeed,
it has been suggested that, in E. coli , the upregulation of hmp via the
m
M GSNO releases less than 5
m
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