Variability analyses of functional domains within glucosamine-6-phosphate synthase of mycosescausing fungi

Responses of Sporothrix globosa to the cell wall perturbing agents Congo Red and Calcofluor White

It is well documented that disturbance of cell surface by some agents triggers compensatory responses aimed to maintain the cell wall integrity in fungi and other organisms. Here, the thermodimorphic fungus Sporothrix globosa, a member of the pathogenic clade of the Sporothrix complex, was propagated in yeast-peptone-dextrose medium under conditions to obtain the mycelium (pH 4.5, 27-28 °C) or the yeast (pH 7.8, 32-34 °C) morphotypes in the absence and presence of the wall-interacting dyes Congo Red (CR) and Calcofluor White (CFW) either alone or in combination. After different periods of time, growth, cell morphology and activity of glucosamine-6-phosphate synthase (GlcN-6-P synthase), an ubiquitous enzyme that plays a crucial role in cell wall biogenesis, were determined. CR and to a lower extent CFW affected growth and morphology of both fungal morphotypes and significantly increased enzyme activity. Notoriously, CR or CR in combination with CFW induced the transient conversion of yeasts into conidia-forming filamentous cells even under culture conditions adjusted for yeast development, most likely as a strategy to evade the noxious effect of the dye. After sometime, hypha returned to yeast cells. An hypothetical model to explain the effect of CR on morphology and enzyme activity based on the possible role of membrane-spanning proteins known as mechanosensors is proposed. Results are discussed in terms of the fungal responses to cell wall damage.

Design, synthesis and pharmacological studies of some new quinoline Schiff bases and 2,5-(disubstituted-[1,3,4])-oxadiazoles

G6P-Ligand (4f) and (5b) interactions as visualized using Chimera (Version 1.8).

Study on variability assessment and evolutionary relationships of glutamate racemase in Pseudomonas species

Pseudomonas species is known to cause multiple nosocomial infections in patients and results in high morbidity and mortality rates (10%). The greatest obstacle in treating patients infected with the Pseudomonas species is the widespread emergence of antibiotic resistance. Hence, there is an urgent need to develop new compounds which can be effective against Pseudomonas species and possibly remain tolerant to drug resistance. The enzyme glutamate racemase plays an important role in cell wall synthesis of bacteria and as a rate limiting step, thus it is an excellent target for the designing of new class of antibacterial agents. The objective of this study is to investigate the variations in sequences of glutamate racemase, a potential drug target across the all 31 species of Pseudomonas. Sequence variability and conservation for functional motif identification is helpful for identifying evolutionarily important residues with functional significance; subsequently these results of variable sites were supported by entropy profile obtained from protein variability server using Shannon entropy. Phylogenetic profile among the different Pseudomonas sp. having fully/highly conserved residues was observed, suggesting possible functional similarities between them. The variation analysis in conserved and non-conserved region of the sequence can be used to predict the binding site for target specific drug discovery.

Molecular docking of glucosamine-6-phosphate synthase in Rhizopus oryzae

Recent expansion of immunocompromised population has led to significant rise in zygomycosis caused by filamentous fungus Rhizopus oryzae. Due to emergence of fungal resistance and side-effects of antifungal drugs, there is increased demand for novel drug targets. The current study elucidates molecular interactions of peptide drugs with G-6-P synthase (catalyzing the rate-limiting step of fungal cell wall biosynthetic pathway) of R.oryzae by molecular docking studies. The PDB structures of enzyme in R.oryzae are not known which were predicted using I-TASSER server and validated with PROCHECK. Peptide inhibitors, FMDP and ADGP previously used against enzyme of E.coli (PDBid: 1XFF), were used for docking studies of enzyme in R.oryzae by SchrödingerMaestro v9.1. To investigate binding between enzyme and inhibitors, Glide and Induced Fit docking were performed. IFD results of 1XFF with FMDP yielded C1, R73, W74, T76, G99 and D123 as the binding sites. C379 and Q427 appear to be vital for binding of R.oryzae enzymes to inhibitors. The comparison results of IFD scores of enzyme in R.oryzae and E.coli (PDBid: 2BPL) yield appreciable score, hinting at the probable effectiveness of inhibitors FMDP and ADGP against R.oryzae, with ADGP showing an improved enzyme affinity. Moreover, the two copies of gene G-6-P synthase due to extensive fungal gene duplication, in R. oryzae eliminating the problem of drug ineffectiveness could act as a potential antifungal drug target in R. oryzae with the application of peptide ligands.

Functional co-evolutionary study of glucosamine-6-phosphate synthase in mycoses causing fungi

Invasive fungal opportunistic infections or mycoses have been on the rise with increase in the number of immuno-compromised patients accounting for associated high morbidity and mortality rates. The antifungal drugs are not completely effective due to increased resistance and varied susceptibility of fungi. Hence, the functional diversification study of novel targets has to be carried out. The enzyme glucosamine-6-phosphate synthase [EC 2.6.1.16], a novel drug target, catalyzes the rate-limiting step of the fungal cell-wall biosynthetic pathway, comprising four conserved domains, two glutaminase and sugar-isomerising (SIS) domains with active site. The amino acids within these domains tend to mutate simultaneously and exert mutual selective forces which might result in untoward fungal adaptations that are fixed through random genetic drift over time. The current study is an attempt to investigate such 'non-independent' coevolving residues which play critical functional and structural role in the protein. Residues with Shannon entropy ≦1 (calculated by the Protein Variability Server) were considered and subsequently, positional correlations were estimated by InterMap3D 1.3 server. It was observed that majority of coevolving pairs of first SIS domain involved interactions with hydrophobic leucine and found to be spatially coupled in 3-dimensional structure of the enzyme. The coevolving groups of Aspergillus niger and Rhizopus oryzae species might play a role in drug resistance. Such coevolutionary analysis is important for understanding the receptor-ligand interactions and effective drug designing.