Spectroscopic, catalytic and binding properties of Bacillus subtilis NO synthase-like protein: comparison with other bacterial and mammalian NO synthases

Nitrosylmyoglobin formation in meat by Lactobacillus fermentum AS1.1880 is due to its nitric oxide synthase activity

The objective of this study was to clarify whether formation of nitrosylmyoglobin (MbFe^IINO) by Lactobacillus fermentum AS1.1880 in meat is due to nitric oxide synthase (NOS) activity. Confocal laser scanning microscopy exhibited strong green fluorescence in the L. fermentum sample treated with a nitric oxide (NO)-specific probe, directly indicating that NO was produced. Furthermore, determination of NOS activity based on the presence of NO metabolites indicated the existence of NOS in L.fermentum. A NOS inhibitor, N^G-nitro-L-arginine methyl ester, significantly inhibited the activity of NOS in L.fermentum (P < 0.05). Futhermore, NOS protein was detected in L.fermentum by Western blot analysis. L-arginine addition largely increased the NOS activity of L.fermentum (P < 0.05). In meat batters, the redness of a sample inoculated with L.fermentum was higher than that of the control and colour was significantly improved with the addition of L-arginine (P < 0.05), indicating that more MbFe^IINO was formed.

The Response of nor and nos Contributes to Staphylococcus aureus Virulence and Metabolism

Staphylococcus aureus causes a wide spectrum of disease, with the site and severity of infection dependent on virulence traits encoded within genetically distinct clonal complexes (CCs) and bacterial responses to host innate immunity. The production of nitric oxide (NO) by activated phagocytes is a major host response to which S. aureus metabolically adapts through multiple strategies that are conserved in all CCs, including an S. aureus nitric oxide synthase (Nos). Previous genome analysis of CC30, a lineage associated with chronic endocardial and osteoarticular infections, revealed a putative NO reductase (Nor) not found in other CCs that potentially contributes to NO resistance and clinical outcome. Here, we demonstrate that Nor has true nitric oxide reductase activity, with nor expression enhanced by NO stress and anaerobic growth. Furthermore, we demonstrate that nor is regulated by MgrA and SrrAB, which modulate S. aureus virulence and hypoxic response. Transcriptome analysis of the S. aureus UAMS-1, UAMS-1 Δnor, and UAMS-1 Δnos strains under NO stress and anaerobic growth demonstrates that Nor contributes to nucleotide metabolism and Nos to glycolysis. We demonstrate that Nor and Nos contribute to enhanced survival in the presence of human human polymorphonuclear cells and have organ-specific seeding in a tail vein infection model. Nor contributes to abscess formation in an osteological implant model. We also demonstrate that Nor has a role in S. aureus metabolism and virulence. The regulation overlap between Nor and Nos points to an intriguing link between regulation of intracellular NO, metabolic adaptation, and persistence in the CC30 lineage.IMPORTANCE Staphylococcus aureus can cause disease at most body sites, and illness spans asymptomatic infection to death. The variety of clinical presentations is due to the diversity of strains, which are grouped into distinct clonal complexes (CCs) based on genetic differences. The ability of S. aureus CC30 to cause chronic infections relies on its ability to evade the oxidative/nitrosative defenses of the immune system and survive under different environmental conditions, including differences in oxygen and nitric oxide concentrations. The significance of this work is the exploration of unique genes involved in resisting NO stress and anoxia. A better understanding of the functions that control the response of S. aureus CC30 to NO and oxygen will guide the treatment of severe disease presentations.

Molecular insights into frataxin-mediated iron supply for heme biosynthesis in Bacillus subtilis

Iron is required as an element to sustain life in all eukaryotes and most bacteria. Although several bacterial iron acquisition strategies have been well explored, little is known about the intracellular trafficking pathways of iron and its entry into the systems for co-factor biogenesis. In this study, we investigated the iron-dependent process of heme maturation in Bacillus subtilis and present, for the first time, structural evidence for the physical interaction of a frataxin homologue (Fra), which is suggested to act as a regulatory component as well as an iron chaperone in different cellular pathways, and a ferrochelatase (HemH), which catalyses the final step of heme b biogenesis. Specific interaction between Fra and HemH was observed upon co-purification from crude cell lysates and, further, by using the recombinant proteins for analytical size-exclusion chromatography. Hydrogen-deuterium exchange experiments identified the landscape of the Fra/HemH interaction interface and revealed Fra as a specific ferrous iron donor for the ferrochelatase HemH. The functional utilisation of the in vitro-generated heme b co-factor upon Fra-mediated iron transfer was confirmed by using the B. subtilis nitric oxide synthase bsNos as a metabolic target enzyme. Complementary mutational analyses confirmed that Fra acts as an essential component for maturation and subsequent targeting of the heme b co-factor, hence representing a key player in the iron-dependent physiology of B. subtilis.

Structural and biological studies on bacterial nitric oxide synthase inhibitors

Nitric oxide (NO) produced by bacterial NOS functions as a cytoprotective agent against oxidative stress in Staphylococcus aureus, Bacillus anthracis, and Bacillus subtilis. The screening of several NOS-selective inhibitors uncovered two inhibitors with potential antimicrobial properties. These two compounds impede the growth of B. subtilis under oxidative stress, and crystal structures show that each compound exhibits a unique binding mode. Both compounds serve as excellent leads for the future development of antimicrobials against bacterial NOS-containing bacteria.

EPR characterisation of the ferrous nitrosyl complex formed within the oxygenase domain of NO synthase

Nitric oxide is produced in mammals by a class of enzymes called NO synthases (NOSs). It plays a central role in cellular signalling but also has deleterious effects, as it leads to the production of reactive oxygen and nitrogen species. NO forms a relatively stable adduct with ferrous haem proteins, which, in the case of NOS, is also a key catalytic intermediate. Despite extensive studies on the ferrous nitrosyl complex of other haem proteins (in particular myoglobin), little characterisation has been performed in the case of NOS. We report here a temperature-dependent EPR study of the ferrous nitrosyl complex of the inducible mammalian NOS and the bacterial NOS-like protein from Bacillus subtilis. The results show that the overall behaviours are similar to those observed for other haem proteins, but with distinct ratios between axial and rhombic forms in the case of the two NOS proteins. The distal environment appears to control the existence of the axial form and the evolution of the rhombic form.

Heme protein and hydroxyarginase necessary for biosynthesis of D-cycloserine

We have recently cloned a D-cycloserine (DCS) biosynthetic gene cluster that consists of 10 genes, designated dcsA~dcsJ, from Streptomyces lavendulae ATCC 11924 (16). In the predicted pathway of hydroxyurea (HU) formation in DCS biosynthesis, L-arginine (L-Arg) must first be hydroxylated, prior to the hydrolysis of N(ω)-hydroxy-L-arginine (NHA) by DcsB, an arginase homolog. The hydroxylation of L-Arg is known to be catalyzed by nitric oxide synthase (NOS). In this study, to verify the supply route of HU, we created a dcsB-disrupted mutant, ΔdcsB. While the mutant lost DCS productivity, its productivity was restored by complementation of dcsB, and also by the addition of HU but not NHA, suggesting that HU is supplied by DcsB. A NOS-encoding gene, nos, from S. lavendulae chromosome was cloned, to create a nos-disrupted mutant. However, the mutant maintained the DCS productivity, suggesting that NOS is not necessary for DCS biosynthesis. To clarify the identity of an enzyme necessary for NHA formation, a dcsA-disrupted mutant, designated ΔdcsA, was also created. The mutant lost DCS productivity, whereas the DCS productivity was restored by complementation of dcsA. The addition of NHA to the culture medium of ΔdcsA mutant was also effective to restore DCS production. These results indicate that the dcsA gene product, DcsA, is an enzyme essential to generate NHA as a precursor in the DCS biosynthetic pathway. Spectroscopic analyses of the recombinant DcsA revealed that it is a heme protein, supporting an idea that DcsA is an enzyme catalyzing hydroxylation.