Coproporphyrin excretion and low thiol levels caused by point mutation in the Rhodobacter sphaeroides S-adenosylmethionine synthetase gene

Detection and Sequencing of Iron Superoxide Dismutase Gene in Entamoeba histolytica Isolated from Patients with Diarrhea in Iraq

Parasites are among serious health problems that threaten the public health of humans. Entamoeba histolytica is considered the second or third most common cause of death among parasitic diseases. The present study was conducted to determine the molecular detection and sequencing of iron-containing superoxide dismutase (FeSOD) genes of E. histolytica. This cross-sectional study was carried out within March-August 2020. Genomic DNA from stool samples was extracted using an AccuPrep® stool DNA Extraction Kit. Afterward, four DNA samples were subjected to sequence alignment analysis of the FeSOD gene in local E. histolytica human isolated using a Clustal W alignment tool (Mega 6.0).The iron-containing superoxide dismutase gene was present at 62.8% in 15 out of 24 E. histolytica samples. The results of sequence alignment analysis of the FeSOD gene in local E.histolytica human isolates indicated the number of mutations in each of the 4 isolates. Accordingly, there were 2 (16.66%) silent mutations and 1(6.66%) nonsense mutation. There are a variety of genetic strains of E. histolytica associated with diarrheal illness in Iraqi patients, which are unique to this country.

Porphyrin Excretion Resulting From Mutation of a Gene Encoding a Class I Fructose 1,6-Bisphosphate Aldolase in Rhodobacter capsulatus

This paper describes a mutant (called SB1707) of the Rhodobacter capsulatus wild type strain SB1003 in which a transposon-disrupted rcc01707 gene resulted in a ∼25-fold increase in the accumulation of coproporphyrin III in the medium of phototrophic (anaerobic) cultures grown in a yeast extract/peptone medium. There was little or no stimulation of pigment accumulation in aerobic cultures. Therefore, this effect of rcc01707 mutation appears to be specific for the anaerobic coproporphyrinogen III oxidase HemN as opposed to the aerobic enzyme HemF. The protein encoded by rcc01707 is homologous to Class I fructose 1,6-bisphosphate aldolases, which catalyze a glycolytic reaction that converts fructose 1, 6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, precursors of pyruvate. There were significant differences in coproporphyrin III accumulation using defined media with individual organic acids and sugars as the sole carbon source: pyruvate, succinate and glutamate stimulated accumulation the most, whereas glucose suppressed coproporphyrin III accumulation to 10% of that of succinate. However, although quantitatively lesser, similar effects of carbon source on the amount of accumulated pigment in the culture medium were seen in a wild type control. Therefore, this mutation appears to exaggerate effects also seen in the wild type strain. It is possible that mutation of rcc01707 causes a metabolic bottleneck or imbalance that was not rectified during growth on the several carbon sources tested. However, we speculate that, analogous to other fructose 1,6-bisphosphate aldolases, the rcc01707 gene product has a “moonlighting” activity that in this case is needed for the maximal expression of the hemN gene. Indeed, it was found that the rcc01707 gene is needed for maximal expression of a hemN promoter-lacZ reporter. With the decrease in hemN expression due to the absence of the rcc01707 gene product, coproporphyrinogen III accumulates and is released from the cell, yielding the spontaneous oxidation product coproporphyrin III.

Iron-modulated virulence factors of Entamoeba histolytica

Entamoeba histolytica is a human parasite that causes amoebiasis, a disease that affects the colon and liver and is prevalent worldwide. This protozoan requires a high concentration of iron to survive and reproduce. Iron modulates the expression of parasite virulence factors, including hemoglobinases, hemoglobin-binding proteins and cysteine proteases, as well as proteins related to the amoebic cytoskeleton. This review summarizes the virulence factors that are affected by iron, resulting in upregulation or downregulation of E. histolytica genes. This review also discusses the functionality of iron in the mechanisms of pathogenesis.

Role of HemF and HemN in the heme biosynthesis of Vibrio vulnificus under S-adenosylmethionine-limiting conditions

Vibrio vulnificus contains two coproporphyrinogen III oxidases (CPOs): O2-dependent HemF and O2-independent HemN. The growth of the hemF mutant HF1 was similar to wild-type cells at pH 7.5 under 2% O2 conditions where HemN was active and had a half-life of 64 min. However, HF1 did not grow when the medium pH decreased to pH 5.0, where oxidative stress affects endogenous S-adenosylmethionine (SAM) levels. The growth of HF1 was restored not only by elevating the expression of MnSOD but also through the exogenous addition of SAM. For HF1 to grow under these SAM-limiting conditions, a mutation arose in hemN, encoding HemNY74F . Refolding of the denatured enzymes in vitro revealed that the apparent binding affinity of HemNY74F for the cofactor SAM1, which coordinates the 4Fe-4S cluster, was approximately sixfold higher than that of HemN. The Km of HemNY74F for the co-substrate SAM2, which provides radicals for CPO reactions, was threefold lower than that of HemN. Thus, affinities for both SAM1 and SAM2 were higher with the Y74F mutation. Taken together, when SAM is limiting, HemN is apparently nonfunctional, and heme synthesis is continued by HemF.

Gene expression profiling in Entamoeba histolytica identifies key components in iron uptake and metabolism

Entamoeba histolytica is an ameboid parasite that causes colonic dysentery and liver abscesses in humans. The parasite encounters dramatic changes in iron concentration during its invasion of the host, with relatively low levels in the intestinal lumen and then relatively high levels in the blood and liver. The liver notably contains sources of iron; therefore, the parasite's ability to use these sources might be relevant to its survival in the liver and thus the pathogenesis of liver abscesses. The objective of the present study was to identify factors involved in iron uptake, use and storage in E. histolytica. We compared the respective transcriptomes of E. histolytica trophozoites grown in normal medium (containing around 169 µM iron), low-iron medium (around 123 µM iron), iron-deficient medium (around 91 µM iron), and iron-deficient medium replenished with hemoglobin. The differentially expressed genes included those coding for the ATP-binding cassette transporters and major facilitator transporters (which share homology with bacterial siderophores and heme transporters) and genes involved in heme biosynthesis and degradation. Iron deficiency was associated with increased transcription of genes encoding a subset of cell signaling molecules, some of which have previously been linked to adaptation to the intestinal environment and virulence. The present study is the first to have assessed the transcriptome of E. histolytica grown under various iron concentrations. Our results provide insights into the pathways involved in iron uptake and metabolism in this parasite.

Detrimental effect of the 6 His C-terminal tag on YedY enzymatic activity and influence of the TAT signal sequence on YedY synthesis

Background

YedY, a molybdoenzyme belonging to the sulfite oxidase family, is found in most Gram-negative bacteria. It contains a twin-arginine signal sequence that is cleaved after its translocation into the periplasm. Despite a weak reductase activity with substrates such as dimethyl sulfoxide or trimethylamine N-oxide, its natural substrate and its role in the cell remain unknown. Although sequence conservation of the YedY family displays a strictly conserved hydrophobic C-terminal residue, all known studies on Escherichia coli YedY have been performed with an enzyme containing a 6 histidine-tag at the C-terminus which could hamper enzyme activity.

Results

In this study, we demonstrate that the tag fused to the C-terminus of Rhodobacter sphaeroides YedY is detrimental to the enzyme’s reductase activity and results in an eight-fold decrease in catalytic efficiency. Nonetheless this C-terminal tag does not influence the properties of the molybdenum active site, as assayed by EPR spectroscopy. When a cleavable His-tag was fused to the N-terminus of the mature enzyme in the absence of the signal sequence, YedY was expressed and folded with its cofactor. However, when the signal sequence was added upstream of the N-ter tag, the amount of enzyme produced was approximately ten-fold higher.

Conclusion

Our study thus underscores the risk of using a C-terminus tagged enzyme while studying YedY, and presents an alternative strategy to express signal sequence-containing enzymes with an N-terminal tag. It brings new insights into molybdoenzyme maturation in R. sphaeroides showing that for some enzymes, maturation can occur in the absence of the signal sequence but that its presence is required for high expression of active enzyme.