jejuni shown to be involved in superoxide and peroxide defence [41] and it is likely that the induction of Dps is a consequence of the iron released upon acid stress. The induced 19 kDa protein (Cj1659) is a well-conserved periplasmic protein in C. jejuni and Campylobacter coli species [50] which previously was found to be Fur like (ferric uptake regulator) and iron regulated [20]. The p19 system is associated with an ABC iron transport system (cj1659 cj1663) [46] and up-regulation of the 19 kDa protein therefore indicates a way to control the intracellular
iron level during acid stress. The thioredoxin system is composed of both TrxB and NADPH. In E. coli, TrxB interacts with unfolded and denatured proteins in a way comparable with molecular chaperones which are involved in proper folding #KPT-8602 mw randurls[1|1|,|CHEM1|]# of mis-folded proteins after stress [51]. A similar function of TrxB in C. jejuni might be possible INK1197 as a part of the acid defence mechanisms. TrxB might mediate alkyl hydroperoxide reductase (AhpC) as is the case of H. pylori[37, 52]. During the acid stress response, the enzyme MogA was induced, which to our knowledge has not been
related to acid response before. However, an unpublished microarray study supported our result with acid exposure conditions comparable with our study (HCl exposure at pH 5.0 in strain NCTC 11168). After 10 minutes up-regulation mogA was measured, but only on the limit of the statistical threshold (Arnoud van Vliet, personal communications). MogA catalyzes the incorporation of molybdenum (Mo) into molybdopterin to form molybdenum cofactor (MoCo), a cofactor in molybdoenzymes [53]. Some molybdoenzymes in E. coli contain a modified form of MoCo. By transferring a GMP (guanosine monophosphate)
to the terminal phosphate of MoCo, a molybdenum guanine dinucleotide (MGD) is formed. MGD is present in the enzymes formate dehydrogenase (FdhA) and nitrate reductase (NapA) in E. coli[54, 55]. The periplasmic two-subunit complex, C. jejuni NAP, Tryptophan synthase is considered as an electron acceptor [56] and the enzyme is encoded by napAGHBLD[13]. The NapA is a ~105 kDa catalytic subunit protein that binds the cofactor MGD. Basically, during electron transport at low O2, the molybdenum-containing enzyme nitrate reductase reduces NO3 – to NO2 – by consuming 2 H+. A transcriptional profile of C. jejuni NCTC 11168 after exposure to HCl stress resulted in a transiently or constantly up-regulated napGHB and fdhA[24], indicating that MogA most likely is part of an acid stress response. The weak induction of SodB and AhpC indicate that the enzymatic oxidative stress defence play a role during acid stress. AhpC eliminates oxidative damaging compounds by converting alkyl hydroperoxides to the corresponding alcohol [37], and during this reaction a proton is consumed. SodB eliminates the damaging super oxides (O2 -) [37, 57], and in this reaction, protons are also consumed thereby preventing acidification of the cytoplasm.