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Currently, there is no three-dimensional structure of D-specific dehalogenase (DehD) in the protein database. We modeled DehD using ab initio technique, performed molecular dynamics (MD) simulation and docking of D-2-chloropropionate (D-2CP), D-2-bromopropionate (D-2BP), monochloroacetate (MCA), monobromoacetate (MBA), 2,2-dichloropropionate (2,2-DCP), D,L-2,3-dichloropropionate (D,L-2,3-DCP), and 3-chloropropionate (3-CP) into the DehD active site. The sequences of DehD and D-2-haloacid dehalogenase (HadD) from Pseudomonas putida AJ1 have 15% sequence similarity. The model had 80% of the amino acid residues in the most favored region when compared to the crystal structure of DehI from Pseudomonas putida PP3. Docking analysis revealed that Arg107, Arg134 and Tyr135 interacted with D-2CP, and Glu20 activated the water molecule for hydrolytic dehalogenation. Single residue substitutions at 25–30 °C showed that polar residues of DehD were stable when substituted with nonpolar residues and showed a decrease in activity within the same temperature range. The molecular dynamics simulation of DehD and its variants showed that in R134A variant, Arg107 interacted with D-2CP, while in Y135A, Gln221 and Arg231 interacted with D-2CP. It is our emphatic belief that the new model will be useful for the rational design of DehDs with enhanced potentials.

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Halogenated compounds are recalcitrant environmental pollutants prevalent in agricultural fields, waste waters and industrial by-products, but they can be degraded by dehalogenase-containing microbes. Notably, 2-haloalkanoic acid dehalogenases are employed to resolve optically active chloropropionates, as exemplified by the d-specific dehalogenase from Rhizobium sp. RCI (DehD), which acts on d-2-chloropropionate but not on its l-enantiomer. The catalytic residues of this dehalogenase responsible for its affinity toward d-2-chloropropionate have not been experimentally determined, although its three-dimensional crystal structure has been solved. For this study, we performed in silico docking and molecular dynamic simulations of complexes formed by this dehalogenase and d- or l-2-chloropropionate. Arg134 of the enzyme plays the key role in the stereospecific binding and Arg16 is in a position that would allow it to activate a water molecule for hydrolytic attack on the d-2-chloropropionate chiral carbon for release of the halide ion to yield l-2-hydroxypropionate. We propose that within the DehD active site, the NH group of Arg134 can form a hydrogen bond with the carboxylate of d-2-chloropropionate with a strength of ∼4 kcal/mol that may act as an acid–base catalyst, whereas, when l-2-chloropropionate is present, this bond cannot be formed. The significance of the present work is vital for rational design of this dehalogenase in order to confirm the involvement of Arg16 and Arg134 residues implicated in hydrolysis and binding of d-2-chloropropionate in the active site of d-specific dehalogenase from Rhizobium sp. RC1.

Diarrhoea is a leading cause of deaths amongst children below five years. Annona senegalensis plant is used traditionally to treat diarrhoea. This study aims at evaluating the antidiarrhoeal potency of the aqueous root and stem bark extracts of Annona senegalensis. Antimicrobial, antioxidant and antidiarrhoeal activity of aqueous extracts of the root bark (ARB), stem bark (ASB) and mixture of stem and root barks (AM) of Annona senegalensis were assessed. Stool inhibition, enteropooling, inhibition of gastro-intestinal motility and electrolyte secretion potential of the extracts were assessed in castor oil-induced diarrhoeic rats following administration of 100, 200 and 400 mg/kg body weight ASB, ARB and AM. The aqueous stem bark (ASB) had the greatest total antioxidant capacity, H2O2 scavenging activity and the ferric reducing assay power. The zone of inhibition of AM against Escherichia coli, Bacillus aureus and Shigella dysentriae was greater than 6 mm. All the extracts inhibited stooling by a percentage ranging from 17-24.7 but was significantly lower (p < 0.05) than the standard drug (30.0%). Inhibition of gastrointestinal tract transit was significantly increased by all the extracts but low dose (100 mg/kg b. wt. of ARB and ASB) significantly increased it the most. The weight and volume of intestinal fluid was significantly decreased by 100 mg/kg b. wt. ARB. The mixture (AM) exhibited synergistic antimicrobial effect. The aqueous stem bark exhibited good antioxidant property, antisecretory and proabsorptive property while the root exhibited good antienteropooling activity. Isolation of bioactive compounds in the extracts should be carried out.

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Africa is rich in a wide range of flora that are exploited as herbal medicines and remedies. Several diseases such as diabetes, diarrhea, dysentery and jaundice have been successfully managed using herbal medicines. Herbal decoctions or concoctions have been used as pain killers, antibiotics, and hematinics. This study evaluated the hematopoietic and biochemical properties of the stem bark of Sterculia setigera Del. in Wistar rats. Results showed that S. setigera decoction has copiously high tannin and cardiac glycoside levels. Ingestion of the decoction by rats over a 16-day period significantly (P < 0.05) increased the body weights of rats by 22.4% in the S. setigera-treated group. Hematological profiles showed raised levels of red blood cells, hemoglobin, packed cell volume, mean corpuscular volume, mean cell hemoglobin, mean cell hemoglobin concentration, and platelets, while biochemical parameters showed lower levels of alanine aminotransferase and aspartate aminotransferase, and slight increase in albumin and TP levels. We posit that the results justify the use of the stem bark of S. setigera as a hematinic by traditional medical practitioners and show its relative safety. Further experiments are needed to evaluate its safety.

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