https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/120 2026-04-27T15:59:41Z 2026-04-27T15:59:41Z Dhembla, Chetna Kumar, Ambrish Arya, Richa Kundu, Suman Sundd, Monica https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1543 2025-12-05T12:48:34Z 2023-01-01T00:00:00Z

Title: Mitochondrial Acyl Carrier Protein of Leishmania major Displays Features Distinct from the Canonical Type II ACP Authors: Dhembla, Chetna; Kumar, Ambrish; Arya, Richa; Kundu, Suman; Sundd, Monica Abstract: Prokaryotes synthesize fatty acids using a type II synthesis pathway (FAS). In this process, the central player, i.e., the acyl carrier protein (ACP), sequesters the growing acyl chain in its internal hydrophobic cavity. As the acyl chain length increases, the cavity expands in size, which is reflected in the NMR chemical shift perturbations and crystal structures of the acyl-ACP intermediates. A few eukaryotic organelles, such as plastids and mitochondria, also harbor type II fatty acid synthesis machinery. Plastid FAS from spinach and Plasmodium falciparum has been characterized at the molecular level, but the mitochondrial pathway remains unexplored. Here, we report NMR studies of the mitochondrial acyl-acyl carrier protein intermediates of Leishmania major (acyl-LmACP). Our studies show that LmACP experiences remarkably small conformational changes upon acylation, with perturbations confined to helices II and III only. CastP determined that the cavity size of apo-LmACP (PDB entry 5ZWT) is less than that of Escherichia coli ACP (PDB 1T8K). Thus, the small chemical shift perturbations observed in the LmACP intermediates, coupled with CastP results, suggest an unusually small cavity when fully expanded. The faster rate of C8-LmACP chain hydrolysis compared to E. coli ACP (EcACP) also supports these convictions. Structure comparison of LmACP with other type II ACP disclosed unique differences in the helix I and loop I conformations, as well as several residues present there. Numerous hydrophobic residues in helix I and loop I (conserved in all mitochondrial ACPs) are substituted with hydrophilic residues in the bacterial/plastid type II ACP. For instance, Phe and leucine at positions 14 and 34 in LmACP are substituted with a hydrophilic residue and Ala in bacterial/plastid type II ACP. Mutation of Leu 34 to Ala (corresponding residue in EcACP) resulted in a complete loss of structure, underscoring its importance in maintaining the ACP fold. Thus, our NMR studies, combined with insights from the crystal structure, highlight several unique features of LmACP, distinct from the prokaryote and plastid type II ACP. Given the high sequence identity, the features might be conserved in all mitochondrial ACPs.

2023-01-01T00:00:00Z Sundd, Monica Yadav, Usha Kundu, Suman Dhembla, Chetna https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1491 2025-12-05T12:49:12Z 2022-01-01T00:00:00Z

Title: Lipoate protein ligase B primarily recognizes the C8-phosphopantetheine arm of its donor substrate and weakly binds the acyl carrier protein Authors: Sundd, Monica; Yadav, Usha; Kundu, Suman; Dhembla, Chetna Abstract: Lipoic acid is a sulfur-containing cofactor indispensable for the function of several metabolic enzymes. In microorganisms, lipoic acid can be salvaged from the surroundings by lipoate protein ligase A (LplA), an ATP-dependent enzyme. Alternatively, it can be synthesized by the sequential actions of lipoate protein ligase B (LipB) and lipoyl synthase (LipA). LipB takes up the octanoyl chain from C8-acyl carrier protein (C8-ACP), a byproduct of the type II fatty acid synthesis pathway, and transfers it to a conserved lysine of the lipoyl domain of a dehydrogenase. However, the molecular basis of its substrate recognition is still not fully understood. Using Escherichia coli LipB as a model enzyme, we show here that the octanoyl-transferase mainly recognizes the 4'-phosphopantetheine-tethered acyl-chain of its donor substrate and weakly binds the apo-acyl carrier protein. We demonstrate LipB can accept octanoate from its own ACP and noncognate ACPs, as well as C8-CoA. Furthermore, our 1H saturation transfer difference and 31P NMR studies demonstrate the binding of adenosine, as well as the phosphopantetheine arm of CoA to LipB, akin to binding to LplA. Finally, we show a conserved 71RGG73 loop, analogous to the lipoate-binding loop of LplA, is required for full LipB activity. Collectively, our studies highlight commonalities between LipB and LplA in their mechanism of substrate recognition. This knowledge could be of significance in the treatment of mitochondrial fatty acid synthesis related disorders.

2022-01-01T00:00:00Z Sundd, Monica Nag, Tapas Chandra Dey, Soumil Bose, Samrat Suman Jain https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1490 2025-12-05T12:48:25Z 2023-01-01T00:00:00Z

Title: Therapeutic Potential of Low-Intensity Magnetic Field Stimulation in 6-Hydroxydopamine Rat Model of Parkinson's Disease: From Inflammation to Motor Function Authors: Sundd, Monica; Nag, Tapas Chandra; Dey, Soumil; Bose, Samrat; Suman Jain Abstract: Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder that mainly affects the aged population. Transcranial magnetic field (MF) stimulation has shown to provide temporary motor recovery in neurological disorders. Purpose: The aim of this study was to understand the cellular and molecular mechanism of low-intensity MF stimulation (17.96 µT; 50Hz; 2 h/day, four weeks) in a rat model of severe PD. Methods: A clinically relevant, bilateral striatal 6-hydroxydopamine (6-OHDA) lesioned rat model of severe PD was employed to test the efficacy of low-intensity MF stimulation in the management of motor symptoms. The mechanism of action of MF was dissected by assessing the microglial activation, tissue ultrastructure, and cerebrospinal fluid (CSF) metabolomics using microdialysis. Results: We observed a significant improvement in the postural balance and gait after MF exposure with a significant reduction in the number of activated microglia. There was an improvement in striatal dopaminergic innervation and glutamate levels but it did not reach a level of statistical significance. Conclusion: MF stimulation helped ameliorate the motor deficits and reduced inflammation but was unable to provide a significant change in terms of dopaminergic innervation and metabolic profile in the severe 6-OHDA PD rat model.

2023-01-01T00:00:00Z Sundd, Monica Kumar, Vijay Karalia, Shivani Dangi, Rohit Singh Meena, Vinod Kumar https://dspace.nii.res.in//https://dspace.nii.res.in/handle/123456789/1489 2025-12-05T12:48:32Z 2022-01-01T00:00:00Z

Title: Structural and mechanistic insights into modulation of α-Synuclein fibril formation by aloin and emodin Authors: Sundd, Monica; Kumar, Vijay; Karalia, Shivani; Dangi, Rohit Singh; Meena, Vinod Kumar Abstract: α-Synuclein (α-Syn) aggregation/fibrillation is a leading cause of neuronal death and is one of the major pathogenic factors involved in the progression of Parkinson's' disease (PD). Against this backdrop, discovering new molecules as inhibitors or modulators of α-Syn aggregation/fibrillation is a subject of enormous research. In this study, we have shown modulation, disaggregation, and neuroprotective potential of aloin and emodin against α-Syn aggregation/fibrillation. Thioflavin T (ThT) fluorescence assay showed an increase in lag phase from (51.14 ± 2) h to (68.58 ± 2) h and (74.14 ± 3) h in the presence of aloin and emodin respectively. ANS binding assay represents a modulatory effect of these molecules on hydrophobicity which is crucial for aggregates/fibril formation. NMR spectroscopy and tyrosine quenching studies reveal the binding of aloin/emodin with monomeric α-Syn. TEM and DLS micrographs illustrate the attenuating effect of aloin/emodin against the development of large aggregates/fibrils. Our seeding experiments suggest aloin/emodin generate seeding incompetent oligomers that direct the off-pathway aggregation/fibrillation. Also, aloin/emodin capably reduces the fibrils-induced cytotoxicity and disassembles the preexisting amyloid fibrils. These findings provide deep insight into the modulatory mechanism of α-Syn aggregation/fibrillation in the presence of aloin and emodin, thereby suggesting their potential roles as promising therapeutic molecules against aggregation/fibrillation related disorders.

2022-01-01T00:00:00Z