Bacterial Hemoglobins and Flavohemoglobins for Alleviation of Nitrosative Stress in Escherichia coli

Abstract

Escherichia coli MG1655 cells expressing novel bacterial hemoglobin and flavohemoglobin genes from a medium-copy-number plasmid were grown in shake flask cultures under nitrosative and oxidative stress. E. coli cells expressing these proteins display enhanced resistance against the NO ⅐ releaser sodium nitroprusside (SNP) relative to that of the control strain bearing the parental plasmid. Expression of bacterial hemoglobins originating from Campylobacter jejuni (CHb) and Vitreoscilla sp. (VHb) conferred resistance on SNP-challenged cells. In addition, it has been shown that NO ⅐ detoxification is also a common feature of flavohemoglobins originating from different taxonomic groups and can be transferred to a heterologous host. These observations have been confirmed in a specific in vitro NO ⅐ consumption assay. Protein extracts isolated from E. coli strains overexpressing flavohemoglobins consumed authentic NO ⅐ more readily than protein extracts from the wildtype strain. Oxidative challenge to the cells evoked nonuniform responses from the various cell cultures. Improved oxidative-stress-sustaining properties had also been observed when the flavohemoglobins from E. coli, Klebsiella pneumoniae, Deinococcus radiodurans, and Pseudomonas aeruginosa were expressed in E. coli.

Maintenance of Nitric Oxide and Redox Homeostasis by the Salmonella Flavohemoglobin Hmp

“…Single domain globins are produced by a small number of bacterial species such as Vitreoscilla sp., Campylobacter jejuni, and Mycobacterium bovis (51,52). But the role of these globins is unclear.…”

Susceptibility of Gram-positive and -negative bacteria to novel nitric oxide-releasing nanoparticle technology

“…[25][26][27] Additionally, Gram-negative bacteria such as E. coli, K. pneumoniae and P. aeruginosa synthesize flavohemoglobins (Hmp), enzymes that neutralize NO and therefore counteract nitrosative stress. 28 Under aerobic conditions, Hmp are upregulated in the presence of NO acting as a denitrosylase that downgrade NO to a harmless NO 3 -ion. Therefore it was not surprising that Bioscreen and CFU analysis demonstrated that the Gram-positive organisms were more susceptible to NO-np, requiring lower concentrations to achieve a significant inhibitory effect on growth and survival as compared to the Gram-negative organisms evaluated.…”

An Unconventional Hexacoordinated Flavohemoglobin from Mycobacterium tuberculosis

“…1B) and modulates the geometry of proximal site is substituted by an alanine. The data suggest that the proximal histidine of MtbFHb lacks the peroxidase-like imidazolate character present in a typical FHb (7,20). The reductase domain of MtbFHb is also highly modified.…”

“…The most notable difference is the lack of hydrogen-bonding interactions between F8H-H23E-G5Y (Fig. 1, A and B) at the proximal site that is conserved among FHb family (7,8). Additionally, H12Y that interacts directly with G5Y (Fig.…”

“…The adaptability of tubercle bacillus within the intracellular environment, where a high level of toxic reactive species and scarcity of oxygen limits its survival, depends primarily on its specialized multi-tier defense system and metabolic flexibility to balance the oxidative/reductive reactions for energy generation (4 -6). Flavohemoglobins (FHbs), 4 carrying an oxygen binding globin domain and a FAD binding reductase domain, constitute an integral part of virulence and stress response in several pathogenic microbes due to their ability to maintain the cell redox homeostasis at the aerobic/anaerobic interface and scavenge nitric oxide (NO) with high efficiency (7)(8)(9). In M. tuberculosis, a similar function is carried out by a single-domain truncated hemoglobin, HbN, that displays a potent nitric oxide dioxygenase activity and detoxifies NO 15-fold faster than myoglobin (10,11), very similar to FHbs.…”