Rv0100, a proposed acyl carrier protein in Mycobacterium tuberculosis: expression, purification and crystallization. Corrigendum

The true identity of the protein found in the crystals reported by Bondoc et al. [(2019), Acta Cryst. F75, 646-651] is given.

Rv0100, a proposed acyl carrier protein in Mycobacterium tuberculosis: expression, purification and crystallization

Acyl carrier proteins (ACPs) are important components in fatty-acid biosynthesis in prokaryotes. Rv0100 is predicted to be an essential ACP in Mycobacterium tuberculosis, the pathogen that is the causative agent of tuberculosis, and therefore has the potential to be a novel antituberculosis drug target. Here, the successful cloning and purification of Rv0100 using Mycobacterium smegmatis as a host is reported. Crystals of the purified protein were obtained that diffracted to a resolution of 1.9 Å. Overall, this work lays the foundation for the future pursuit of drug discovery and development against this potentially novel drug target.

Inositol Monophosphatase: A Bifunctional Enzyme in Mycobacterium smegmatis

Inositol monophosphatase (IMPase) is a crucial enzyme for the biosynthesis of phosphatidylinositol, an essential component in mycobacterial cell walls. IMPase A (ImpA) from Mycobacterium smegmatis is a bifunctional enzyme that also functions as a fructose-1,6-bisphosphatase (FBPase). To better understand the bifunctional nature of this enzyme, point mutagenesis was conducted on several key residues and their enzyme activity was tested. Our results along with active site models support the fact that ImpA is a bifunctional enzyme with residues Gly94, Thr95 hypothesized to be contributing to the FBPase activity and residues Trp220, Asp221 hypothesized to be contributing to the IMPase activity. Double mutants, W220A + D221A reduced both FBPase and IMPase activity drastically while the double mutant G94A + T95A surprisingly partially restored the IMPase activity compared to the single mutants. This study establishes the foundation toward obtaining a better understanding of the bifunctional nature of this enzyme.

Nanoparticles against resistant Pseudomonas spp

Pseudomonas spp. collected from areas where human regularly comes into contact with were tested for their susceptibility to antibiotics. Twenty-nine samples were collected and screened for Pseudomonas spp. Of the nine isolated strains Pseudomonas spp. six were resistant to antibiotics. A few were used for an antimicrobial study on the interaction with silver and zinc oxide nanoparticles individually and as a mixture. A mixture of silver and zinc oxide nanoparticles showed synergy against resistant Pseudomonas spp.

Mutagenesis of threonine to serine in the active site of Mycobacterium tuberculosis fructose-1,6-bisphosphatase (Class II) retains partial enzyme activity

The glpX gene encodes for the Class II fructose-1,6-bisphosphatase enzyme in Mycobacterium tuberculosis (Mt), an essential enzyme for pathogenesis. We have performed site directed mutagenesis to introduce two mutations at residue Thr84, T84A and T84S, to explore the binding affinity of the substrate and the catalytic mechanism. The T84A mutant fully abolishes enzyme activity while retaining substrate binding affinity. In contrast, the T84S mutant retains some activity having a 10 times reduction in V_max and exhibited similar sensitivity to lithium when compared to the wildtype. Homology modeling using the Escherichia coli enzyme structure suggests that the replacement of the critical nucleophile OH^- in the Thr84 residue of the wildtype of MtFBPase by Ser84 results in subtle alterations of the position and orientation that reduce the catalytic efficiency. This mutant could be used to trap reaction intermediates, through crystallographic methods, facilitating the design of potent inhibitors via structure-based drug design.

Enzymatic Characterization of Fructose 1,6-Bisphosphatase II from Francisella tularensis, an Essential Enzyme for Pathogenesis

The glpX gene from Francisella tularensis encodes for the class II fructose 1,6-bisphosphatase (FBPaseII) enzyme. The glpX gene has been verified to be essential in F. tularensis, and the inactivation of this gene leads to impaired bacterial growth on gluconeogenic substrates. In the present work, we have complemented a ∆glpX mutant of Escherichia coli with the glpX gene of F. tularensis (FTF1631c). Our complementation work independently verifies that the glpX gene (FTF1631c) in F. tularensis is indeed an FBPase and supports the growth of the ΔglpX E. coli mutant on glycerol-containing media. We have performed heterologous expression and purification of the glpX encoded FBPaseII in F. tularensis. We have confirmed the function of glpX as an FBPase and optimized the conditions for enzymatic activity. Mn²⁺ was found to be an absolute requirement for activity, with no other metal substitutions rendering the enzyme active. The kinetic parameters for this enzyme were found as follows: K_m 11 μM, V_max 2.0 units/mg, k_cat 1.2 s^-1, k_cat/K_m 120 mM^-1 s^-1, and a specific activity of 2.0 units/mg. Size exclusion data suggested an abundance of a tetrameric species in solution. Our findings on the enzyme's properties will facilitate the initial stages of a structure-based drug design program targeting this essential gene of F. tularensis.