A GFP-strategy for efficient recombinant protein overexpression and purification in Mycobacterium smegmatis

One of the major obstacles to obtaining a complete structural and functional understanding of proteins encoded by the Mycobacterium tuberculosis (Mtb) pathogen is due to significant difficulties in producing recombinant mycobacterial proteins. Recent advances that have utilised the closely related Mycobacterium smegmatis species as a native host have been effective. Here we have developed a method for the rapid screening of both protein production and purification strategies of mycobacterial proteins in whole M. smegmatis cells following green fluorescent protein (GFP) fluorescence as an indicator. We have adapted the inducible T7-promoter based pYUB1062 shuttle vector by the addition of a tobacco etch virus (TEV) cleavable C-terminal GFP enabling the target protein to be produced as a GFP-fusion with a poly-histidine tag for affinity purification. We illustrate the advantages of a fluorescent monitoring approach with the production and purification of the mycobacterial N-acetylglucosamine-6-phosphate deacetylase (NagA)-GFP fusion protein. The GFP system described here will accelerate the production of mycobacterial proteins that can be used to understand the molecular mechanisms of Mtb proteins and facilitate drug discovery efforts

Structural and functional determination of homologs of the Mycobacterium tuberculosis N-acetylglucosamine-6-phosphate deacetylase (NagA)

The (Mtb) pathogen encodes an -acetylglucosamine-6-phosphate deacetylase enzyme, NagA (Rv3332), that belongs to the amidohydrolase superfamily. NagA enzymes catalyze the deacetylation of -acetylglucosamine-6-phosphate (GlcNAc6P) to glucosamine-6-phosphate (GlcN6P). NagA is a potential anti-tubercular drug target because it represents the key enzymatic step in the generation of essential amino-sugar precursors required for cell wall biosynthesis and also influences recycling of cell wall peptidoglycan fragments. Here, we report the structural and functional characterization of NagA from (MSNagA) and (MMNagA), close relatives of Using a combination of X-ray crystallography, site-directed mutagenesis, and biochemical and biophysical assays, we show that these mycobacterial NagA enzymes are selective for GlcNAc6P. Site-directed mutagenesis studies revealed crucial roles of conserved residues in the active site that underpin stereo-selective recognition, binding, and catalysis of substrates. Moreover, we report the crystal structure of MSNagA in both ligand-free form and in complex with the GlcNAc6P substrate at 2.6 Å and 2.0 Å resolutions, respectively. The GlcNAc6P-complex structure disclosed the precise mode of GlcNAc6P binding and the structural framework of the active site, including two divalent metals located in the α/β binuclear site. Furthermore, we observed a cysteine residue located on a flexible loop region that occludes the active site. This cysteine is unique to mycobacteria and may represent a unique subsite for targeting mycobacterial NagA enzymes. Our results provide critical insights into the structural and mechanistic properties of mycobacterial NagA enzymes having an essential role in amino-sugar and nucleotide metabolism in mycobacteria

Thiamine responsive megaloblastic anemia syndrome associated with patent ductus arteriosus: First case report from Kashmir Valley of the Indian subcontinent

Thiamine responsive megaloblastic anemia syndrome, an autosomal recessive inherited disorder characterized by a triad of anemia, diabetes mellitus and sensorineural deafness is caused by a deficiency of a thiamine transporter protein. The disorder is rare and has not been reported from our community which has high background of consanguinity. We report a six years old girl who presented with diabetes mellitus which remitted after thiamine replacement. The girl in addition had sensorineural deafness, reinopathy, atrial septal defect and megaloblastic anemia which responded to high doses of thymine. This is the first case reported from Kashmir valley and third from India. The presentation and management in such cases is discussed