Dhiman Ghosh
Indian Institute of Technology Bombay
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Featured researches published by Dhiman Ghosh.
ACS Chemical Neuroscience | 2013
Pradeep K. Singh; Vasudha Kotia; Dhiman Ghosh; Ganesh M. Mohite; Ashutosh Kumar; Samir K. Maji
In human beings, Parkinsons disease (PD) is associated with the oligomerization and amyloid formation of α-synuclein (α-Syn). The polyphenolic Asian food ingredient curcumin has proven to be effective against a wide range of human diseases including cancers and neurological disorders. While curcumin has been shown to significantly reduce cell toxicity of α-Syn aggregates, its mechanism of action remains unexplored. Here, using a series of biophysical techniques, we demonstrate that curcumin reduces toxicity by binding to preformed oligomers and fibrils and altering their hydrophobic surface exposure. Further, our fluorescence and two-dimensional nuclear magnetic resonance (2D-NMR) data indicate that curcumin does not bind to monomeric α-Syn but binds specifically to oligomeric intermediates. The degree of curcumin binding correlates with the extent of α-Syn oligomerization, suggesting that the ordered structure of protein is required for effective curcumin binding. The acceleration of aggregation by curcumin may decrease the population of toxic oligomeric intermediates of α-Syn. Collectively; our results suggest that curcumin and related polyphenolic compounds can be pursued as candidate drug targets for treatment of PD and other neurological diseases.
Biochemistry | 2013
Dhiman Ghosh; Mrityunjoy Mondal; Ganesh M. Mohite; Pradeep K. Singh; Priyatosh Ranjan; A. Anoop; Saikat Kumar B. Ghosh; Narendra Nath Jha; Ashutosh Kumar; Samir K. Maji
α-Synuclein (α-Syn) aggregation is directly linked with Parkinsons disease (PD) pathogenesis. Here, we analyzed the aggregation of newly discovered α-Syn missense mutant H50Q in vitro and found that this mutation significantly accelerates the aggregation and amyloid formation of α-Syn. This mutation, however, did not alter the overall secondary structure as suggested by two-dimensional nuclear magnetic resonance and circular dichroism spectroscopy. The initial oligomerization study by cross-linking and chromatographic techniques suggested that this mutant oligomerizes to an extent similar to that of the wild-type α-Syn protein. Understanding the aggregation mechanism of this H50Q mutant may help to establish the aggregation and phenotypic relationship of this novel mutant in PD.
Biochemistry | 2014
Dhiman Ghosh; Shruti Sahay; Priyatosh Ranjan; Shimul Salot; Ganesh M. Mohite; Pradeep K. Singh; Saumya Dwivedi; Edmund Carvalho; Rinti Banerjee; Ashutosh Kumar; Samir K. Maji
α-Synuclein (α-Syn) oligomerization and amyloid formation are associated with Parkinsons disease (PD) pathogenesis. Studying familial α-Syn mutants associated with early onset PD has therapeutic importance. Here we report the aggregation kinetics and other biophysical properties of a newly discovered PD associated Finnish mutation (A53E). Our in vitro study demonstrated that A53E attenuated α-Syn aggregation and amyloid formation without altering the major secondary structure and initial oligomerization tendency. Further, A53E showed reduced membrane binding affinity compared to A53T and WT. The present study would help to delineate the role of A53E mutation in early onset PD pathogenesis.
Biomaterials | 2015
Reeba S. Jacob; Dhiman Ghosh; Pradeep K. Singh; Santanu Kumar Basu; Narendra Nath Jha; Subhadeep Das; Pradip K. Sukul; Sachin Patil; Sadhana Sathaye; Ashutosh Kumar; Arindam Chowdhury; Sudip Malik; Shamik Sen; Samir K. Maji
Amyloids are highly ordered protein/peptide aggregates associated with human diseases as well as various native biological functions. Given the diverse range of physiochemical properties of amyloids, we hypothesized that higher order amyloid self-assembly could be used for fabricating novel hydrogels for biomaterial applications. For proof of concept, we designed a series of peptides based on the high aggregation prone C-terminus of Aβ42, which is associated with Alzheimers disease. These Fmoc protected peptides self assemble to β sheet rich nanofibrils, forming hydrogels that are thermoreversible, non-toxic and thixotropic. Mechanistic studies indicate that while hydrophobic, π-π interactions and hydrogen bonding drive amyloid network formation to form supramolecular gel structure, the exposed hydrophobic surface of amyloid fibrils may render thixotropicity to these gels. We have demonstrated the utility of these hydrogels in supporting cell attachment and spreading across a diverse range of cell types. Finally, by tuning the stiffness of these gels through modulation of peptide concentration and salt concentration these hydrogels could be used as scaffolds that can drive differentiation of mesenchymal stem cells. Taken together, our results indicate that small size, ease of custom synthesis, thixotropic nature makes these amyloid-based hydrogels ideally suited for biomaterial/nanotechnology applications.
Scientific Reports | 2015
Dhiman Ghosh; Pradeep K. Singh; Shruti Sahay; Narendra Nath Jha; Reeba S. Jacob; Shamik Sen; Ashutosh Kumar; Roland Riek; Samir K. Maji
Mechanistic understanding of nucleation dependent polymerization by α-synuclein (α-Syn) into toxic oligomers and amyloids is important for the drug development against Parkinsons disease. However the structural and morphological characterization during nucleation and subsequent fibrillation process of α-Syn is not clearly understood. Using a variety of complementary biophysical techniques monitoring entire pathway of nine different synucleins, we found that transition of unstructured conformation into β-sheet rich fibril formation involves helix-rich intermediates. These intermediates are common for all aggregating synucleins, contain high solvent-exposed hydrophobic surfaces, are cytotoxic to SHSY-5Y cells and accelerate α-Syn aggregation efficiently. A multidimensional NMR study characterizing the intermediate accompanied with site-specific fluorescence study suggests that the N-terminal and central portions mainly participate in the helix-rich intermediate formation while the C-terminus remained in an extended conformation. However, significant conformational transitions occur at the middle and at the C-terminus during helix to β-sheet transition as evident from Trp fluorescence study. Since partial helix-rich intermediates were also observed for other amyloidogenic proteins such as Aβ and IAPP, we hypothesize that this class of intermediates may be one of the important intermediates for amyloid formation pathway by many natively unstructured protein/peptides and represent a potential target for drug development against amyloid diseases.
Journal of Biological Chemistry | 2015
Shruti Sahay; Dhiman Ghosh; Saumya Dwivedi; A. Anoop; Ganesh M. Mohite; Mamata Kombrabail; G. Krishnamoorthy; Samir K. Maji
Background: Aggregation of α-Syn is associated with PD pathogenesis. Results: Despite being natively unfolded, a site-specific structure exists in α-Syn that is significantly altered by familial PD-associated E46K, A53T, and A30P mutations. Conclusion: Altered site-specific structure of the PD-associated mutants may attribute to their different aggregation propensity. Significance: This study contributes to understanding the relationship between structure and aggregation of α-Syn. Human α-synuclein (α-Syn) is a natively unstructured protein whose aggregation into amyloid fibrils is associated with Parkinson disease (PD) pathogenesis. Mutations of α-Syn, E46K, A53T, and A30P, have been linked to the familial form of PD. In vitro aggregation studies suggest that increased propensity to form non-fibrillar oligomers is the shared property of these familial PD-associated mutants. However, the structural basis of the altered aggregation propensities of these PD-associated mutants is not yet clear. To understand this, we studied the site-specific structural dynamics of wild type (WT) α-Syn and its three PD mutants (A53T, E46K, and A30P). Tryptophan (Trp) was substituted at the N terminus, central hydrophobic region, and C terminus of all α-Syns. Using various biophysical techniques including time-resolved fluorescence studies, we show that irrespective of similar secondary structure and early oligomerization propensities, familial PD-associated mutations alter the site-specific microenvironment, solvent exposure, and conformational flexibility of the protein. Our results further show that the common structural feature of the three PD-associated mutants is more compact and rigid sites at their N and C termini compared with WT α-Syn that may facilitate the formation of a partially folded intermediate that eventually leads to their increased oligomerization propensities.
Langmuir | 2014
Dhiman Ghosh; Paulami Dutta; Chanchal Chakraborty; Pradeep K. Singh; A. Anoop; Narendra Nath Jha; Reeba S. Jacob; Mrityunjoy Mondal; Shruti Mankar; Subhadeep Das; Sudip Malik; Samir K. Maji
It has been suggested that conjugated charged polymers are amyloid imaging agents and promising therapeutic candidates for neurological disorders. However, very less is known about their efficacy in modulating the amyloid aggregation pathway. Here, we studied the modulation of Parkinsons disease associated α-synuclein (AS) amyloid assembly kinetics using conjugated polyfluorene polymers (PF, cationic; PFS, anionic). We also explored the complexation of these charged polymers with the various AS aggregated species including amyloid fibrils and oligomers using multidisciplinary biophysical techniques. Our data suggests that both polymers irrespective of their different charges in the side chains increase the fibrilization kinetics of AS and also remarkably change the morphology of the resultant amyloid fibrils. Both polymers were incorporated/aligned onto the AS amyloid fibrils as evident from electron microscopy (EM) and atomic force microscopy (AFM), and the resultant complexes were structurally distinct from their pristine form of both polymers and AS supported by FTIR study. Additionally, we observed that the mechanism of interactions between the polymers with different species of AS aggregates were markedly different.
Cell Death & Differentiation | 2017
Saikat Kumar B. Ghosh; Shimul Salot; Shinjinee Sengupta; Ambuja Navalkar; Dhiman Ghosh; Reeba S. Jacob; Subhadeep Das; Rakesh Kumar; Narendra Nath Jha; Shruti Sahay; Surabhi Mehra; Ganesh M. Mohite; Santanu Kumar Ghosh; Mamata Kombrabail; G. Krishnamoorthy; Pradip Chaudhari; Samir K. Maji
The transcriptional regulator p53 has an essential role in tumor suppression. Almost 50% of human cancers are associated with the loss of p53 functions, where p53 often accumulates in the nucleus as well as in cytoplasm. Although it has been previously suggested that amyloid formation could be a cause of p53 loss-of-function in subset of tumors, the characterization of these amyloids and its structure-function relationship is not yet established. In the current study, we provide several evidences for the presence of p53 amyloid formation (in human and animal cancer tissues); along with its isolation from human cancer tissues and the biophysical characterization of these tissue-derived fibrils. Using amyloid seed of p53 fragment (P8, p53(250-257)), we show that p53 amyloid formation in cells not only leads to its functional inactivation but also transforms it into an oncoprotein. The in vitro studies further show that cancer-associated mutation destabilizes the fold of p53 core domain and also accelerates the aggregation and amyloid formation by this protein. Furthermore, we also show evidence of prion-like cell-to-cell transmission of different p53 amyloid species including full-length p53, which is induced by internalized P8 fibrils. The present study suggests that p53 amyloid formation could be one of the possible cause of p53 loss of function and therefore, inhibiting p53 amyloidogenesis could restore p53 tumor suppressor functions.
Biochemistry | 2014
Saikat Kumar B. Ghosh; Dhiman Ghosh; Srivastav Ranganathan; A. Anoop; Santosh Kumar P; Narendra Nath Jha; Ranjith Padinhateeri; Samir K. Maji
Protein aggregation and amyloid formation are known to play a role both in diseases and in biological functions. Transcription factor p53 plays a major role in tumor suppression by maintaining genomic stability. Recent studies have suggested that amyloid formation of p53 could lead to its loss of physiological function as a tumor suppressor. Here, we investigated the intrinsic amyloidogenic nature of wild-type p53 using sequence analysis. We used bioinformatics and aggregation prediction algorithms to establish the evolutionarily conserved nature of aggregation-prone sequences in wild-type p53. Further, we analyzed the amyloid forming capacity of conserved and aggregation-prone p53-derived peptides PILTIITL and YFTLQI in vitro using various biophysical techniques, including all atom molecular dynamics simulation. Finally, we probed the seeding ability of the PILTIITL peptide on p53 aggregation in vitro and in cells. Our data demonstrate the intrinsic amyloid forming ability of a sequence stretch of the p53 DNA binding domain (DBD) and its aggregation templating behavior on full-length and p53 core domain. Therefore, p53 aggregation, instigated through an amyloidogenic segment in its DBD, could be a putative driving force for p53 aggregation in vivo.
Journal of Biological Chemistry | 2014
Prasanna K. R. Allu; Venkat R. Chirasani; Dhiman Ghosh; Anitha Mani; Amal Kanti Bera; Samir K. Maji; Sanjib Senapati; Ajit S. Mullasari; Nitish R. Mahapatra
Background: Pancreastatin is a potent physiological regulator of plasma glucose/insulin. Results: We discovered two human variants of pancreastatin that are profoundly more potent than the wild-type peptide. Conclusion: Higher potencies of the variants correlate well with their enhanced propensity to adopt longer helical structures than the wild-type peptide. Significance: These findings provide new insights into the mechanism of human metabolic diseases. Pancreastatin (PST), a chromogranin A-derived peptide, is a potent physiological inhibitor of glucose-induced insulin secretion. PST also triggers glycogenolysis in liver and reduces glucose uptake in adipocytes and hepatocytes. Here, we probed for genetic variations in PST sequence and identified two variants within its functionally important carboxyl terminus domain: E287K and G297S. To understand functional implications of these amino acid substitutions, we tested the effects of wild-type (PST-WT), PST-287K, and PST-297S peptides on various cellular processes/events. The rank order of efficacy to inhibit insulin-stimulated glucose uptake was: PST-297S > PST-287K > PST-WT. The PST peptides also displayed the same order of efficacy for enhancing intracellular nitric oxide and Ca2+ levels in various cell types. In addition, PST peptides activated gluconeogenic genes in the following order: PST-297S ≈ PST-287K > PST-WT. Consistent with these in vitro results, the common PST variant allele Ser-297 was associated with significantly higher (by ∼17 mg/dl, as compared with the wild-type Gly-297 allele) plasma glucose level in our study population (n = 410). Molecular modeling and molecular dynamics simulations predicted the following rank order of α-helical content: PST-297S > PST-287K > PST-WT. Corroboratively, circular dichroism analysis of PST peptides revealed significant differences in global structures (e.g. the order of propensity to form α-helix was: PST-297S ≈ PST-287K > PST-WT). This study provides a molecular basis for enhanced potencies/efficacies of human PST variants (likely to occur in ∼300 million people worldwide) and has quantitative implications for inter-individual variations in glucose/insulin homeostasis.