@article {45687, title = {Kinetics and thermodynamics of transpeptidation catalysed by Bacillus subtilis gamma glutamyl transferase}, journal = {Indian Journal of Biochemistry and Biophysics }, volume = {54 }, year = {2017}, month = {JUN}, pages = {109-113}, type = {Article}, abstract = {Gamma glutamyl transferases (GGT) catalyse the removal (deglutamylation) of the terminal gamma-glutamate residue from compounds such as glutathione and poly-gamma-glutamic acid and its transfer either to a water molecule (hydrolysis) or to a peptide/amino acid (transpeptidation). We analysed the kinetics of Bacillus subtilis GGT (BsGGT) catalysed transpeptidation using gamma-glutamyl-(3-carboxyl)-4-nitroaniline as the gamma-glutamate-donor and glycylglycine (Gly-Gly) as the gamma-glutamate acceptor. Addition of Gly-Gly improved the affinity (Km) of the enzyme for gamma-glutamyl-(3-carboxyl)-4-nitroaniline by nearly 25 times with negligible impact on the rate of deglutamylation (V-max). The asymmetric changes in the kinetic parameters improved the specificity constant (K-cat/K-m.) by about 43 times. BsGGT catalysed transpeptidation was pronounced in conditions that are unfavorable for hydrolysis. Maximum transpeptidation occurred near neutral pH and when the concentration of the gamma-glutamate-donor substrate is lower. The effect of Gly-Gly on the kinetics of BsGGT is contrastingly different from that observed for eukaryotic GGTs. In the case of mammalian GGTs, the addition of Gly-Gly increases both Km and k(cat); and, the specificity constant (K-cat/K-m) remains unaltered}, author = {Balakrishna, Sharath and Prabhune, Asmita A.} } @article {44606, title = {Photophysical studies on curcumin-sophorolipid nanostructures: applications in quorum quenching and imaging}, journal = {Royal Society Open Science}, volume = {5}, year = {2018}, month = {FEB}, pages = {170865}, abstract = {

Sophorolipid biosurfactants are biodegradable, less toxic and FDA approved. The purified acidic form of sophorolipid is stimuli-responsive with self-assembling properties and used for solubilizing hydrophobic drugs. This study encapsulated curcumin (CU) with acidic sophorolipid (ASL) micelles and analysed using photophysical studies like UV-visible spectroscopy, photoluminescence (PL) spectroscopy and timecorrelated single photon counting (TCSPC). TEM images have revealed ellipsoid micelles of approximately 100nm size and were confirmed by dynamic light scattering. The bacterial fluorescence uptake studies showed the uptake of formed CUASL nanostructures into both Gram-positive and Gram-negative bacteria. They also showed quorum quenching activity against Pseudomonas aeruginosa. The results have demonstrated this system has potential theranostic applications.

}, keywords = {curcumin, photophysical, Quorum quenching, Sophorolipid}, issn = {2054-5703}, doi = {10.1098/rsos.170865}, author = {Vasudevan, Sahana and Prabhune, Asmita A.} } @article {46645, title = {Lauric acid sophorolipid: accelerating the gelation of silk fibroin}, journal = {ACS Omega}, volume = {5}, year = {2020}, month = {NOV}, pages = {28571-28578}, type = {Article}, abstract = {

Silk fibroin (SF) hydrogels find wide applications in tissue engineering. However, their scope has been limited due to the long gelation time in ambient conditions. This paper shows the reduction in gelation time of silk fibroin to minutes upon doping with a newly synthesized lauric acid sophorolipid (LASL). LASL comprises a fatty acid, lauric acid (with a 12-carbon aliphatic chain), that is derivatized by glucose molecules using a non-pathogenic yeast Candida bombicola. LASL was characterized using spectroscopic (Fourier transform infrared spectroscopy) and chromatographic (high-performance liquid chromatography, thin-layer chromatography, and high-resolution mass spectrometry) methods. This gelation of SF is comparable to the effect of an anionic surfactant, sodium dodecyl sulfate (SDS). The microstructure of SF-LASL hydrogels was investigated by small-angle neutron scattering (SANS) measurements and exhibited the beads-on-a-necklace model. The rheological properties of these hydrogels show similarity to SF-SDS hydrogels, therefore presenting a greener alternative for tissue engineering applications.

}, issn = {2470-1343}, doi = {10.1021/acsomega.0c03411}, author = {Hirlekar, Swarali and Ray, Debes and Aswal, Vinod K. and Prabhune, Asmita A. and Nisal, Anuya} } @article {47104, title = {Myristic acid derived sophorolipid: efficient synthesis and enhanced antibacterial activity}, journal = {ACS Omega}, volume = {6}, year = {2021}, month = {JAN}, pages = {1273-1279}, type = {Article}, abstract = {

Microbial glycolipids are one of the most interesting alternatives to chemical-based surfactants as they exhibit improved biodegradability and less toxicity. However, their potential has been limited because of specificity of the yeast toward fatty acids having a carbon 16 or carbon 18 chain. This study focuses on sophorolipid (SL) production by the yeast Starmerella bombicola using myristic acid, a medium-chain carbon-14 fatty acid that has not been used as a substrate for SL production. The production was optimized for inoculum size and lipophilic substrate concentration. Furthermore, we also studied the effect of medium-chain fatty acid on yeast cell growth and optimized the process for excellent yield. The myristic acid SL (MASL) so synthesized consisted of mono- and diacetylated forms with preferential glycosylation at the methyl end group, as determined by high-resolution mass spectrometry. Individual congeners of the crude mixture were separated using dry column chromatography and then structurally characterized by mass spectrometry. The synthesized MASL was also shown to have promising surface tension, lowering abilities with a low CMC of 14 mg/L. The SL derived from myristic acid exhibited superior antibacterial activity as compared to SL derived from oleic acid. MASL was also found to be more potent against Gram-positive organisms as compared to Gram-negative organisms. This work, therefore, demonstrates successful synthesis of myristic acid-derived SL and its superior antibacterial activity, establishing a promising future for this biosurfactant.

}, issn = {2470-1343}, doi = {10.1021/acsomega.0c04683}, author = {Abhyankar, Isha and Sevi, Ganesh and Prabhune, Asmita A. and Nisal, Anuya and Bayatigeri, Santhakumari} } @article {47498, title = {Red fluorescent ultra-small gold nanoclusters functionalized with signal molecules to probe specificity in quorum sensing receptors in gram-negative bacteria}, journal = {Archives of Microbiology}, year = {2021}, month = {JUN}, type = {Article; Early Access}, abstract = {Ultra-small (size < 2 nm) gold nanoclusters (AuNCs) are used as fluorescent probes which have excellent applications in bioimaging and sensing due to their emission in visible and NIR spectral region. Here, this property is exploited for understanding the quorum sensing phenomenon in bacteria which is regulated by signal molecules which are specific to various species. AuNCs are then functionalized with the signal molecules, Acyl Homoserine Lactones (AHL) of varying carbon chain length, C-6, C-8, and C-12 without 3rd C modification, to sense different strains of gram-negative bacteria i.e., Escherichia coli, Cronobacter sakazakii and Pseudomonas aeruginosa. In the concentration employed, selectivity to a limited extent is observed between the three Gram-negative bacteria tested. E. coli showed emission with all the AHL conjugates and P. aeruginosa did not interact with any of the three conjugates, whereas C. sakazakii showed specificity to C-8AHL. This is probably due to selectivity for cognate AHL molecules of appropriate concentrations.}, keywords = {acyl homoserine lactone, fluorescence imaging, Gold nanoclusters, quorum sensing, Receptors, selectivity}, issn = {0302-8933}, doi = {10.1007/s00203-021-02338-y, Early Access Date = JUN 2021}, author = {Chahande, Anurag M. and Lathigara, Disha and Prabhune, Asmita A. and Devi, R. Nandini} }