Publications by authors named "Kanchan Garai"

Apolipoprotein E4 (apoE4) is the strongest genetic risk factor for Alzheimer's disease (AD). However, structural differences between apoE4 and the AD-neutral isoform, apoE3, still remain unclear. Recent studies suggest that apoE4 harbors intermediates.

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Alzheimer's disease (AD) is associated with the aggregation of amyloid β (Aβ) and tau proteins. Why ApoE variants are significant genetic risk factors remains a major unsolved puzzle in understanding AD, although intracellular interactions with ApoE are suspected to play a role. Here, we show that specific changes in the fluorescence lifetime of fluorescently tagged small Aβ oligomers in rat brain cells correlate with the cellular ApoE content.

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The formation of amyloid fibrils and oligomers is a hallmark of several neurodegenerative disorders, including Alzheimer's disease (AD), and contributes to the disease pathway. To progress our understanding of these diseases at a molecular level, it is crucial to determine the mechanisms and rates of amyloid formation and replication. In the context of AD, the self-replication of aggregates of the Aβ42 peptide by secondary nucleation, leading to the formation of new aggregates on the surfaces of existing ones, is a major source of both new fibrils and smaller toxic oligomeric species.

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Molecular chaperone Hsp70 plays important roles in the pathology of amyloid diseases by inhibiting aberrant aggregation of proteins. However, the biophysical mechanism of the interaction of Hsp70 with the intrinsically disordered proteins (IDPs) is unclear. Here, we report that Hsp70 inhibits aggregation of islet amyloid polypeptide (IAPP) at substoichiometric concentrations under diverse solution conditions, including in the absence of ATP.

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ApoE4(C112R) is the strongest risk factor for Alzheimer's disease, while apoE3(C112) is considered normal. The C112R substitution is believed to alter the interactions between the N-terminal (NTD) and the C-terminal domain (CTD) leading to major functional differences. Here we investigate how the molecular property of the residue at position 112 affects domain interaction using an array of C112X substitutions with arginine, alanine, threonine, valine, leucine and isoleucine as 'X'.

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Podocytes are crucial cells of the glomerular filtration unit and plays a vital role at the interface of the blood-urine barrier. Podocyte slit-diaphragm is a modified tight junction that facilitates size and charge-dependent permselectivity. Several proteins including podocin, nephrin, CD2AP, and TRPC6 form a macromolecular assembly and constitute the slit-diaphragm.

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Although the interaction of apoE isoforms with amyloid-β (Aβ) peptides plays a critical role in the progression of Alzheimer's disease, how they interact with each other remains poorly understood. Here, we investigate the molecular mechanism of apoE-Aβ interactions by comparing the effects of the different domains of apoE on Aβ. The kinetics of aggregation of Aβ1-42 are delayed dramatically in the presence of substoichiometric, nanomolar concentrations of N-terminal fragment (NTF), C-terminal fragment (CTF) and full-length apoE both in lipid-free and in lipidated forms.

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Article Synopsis
  • The study utilizes NMR to investigate how Aβ1-40 monomers bind transiently to fibers.
  • It identifies that the strongest interactions occur near specific residue pairs (F19-K28) and weaker interactions near the C-terminus (L34-G37).
  • These findings suggest a need to rethink inhibitor designs by moving away from the previously focused KLVFFA sequence (residues 16-21).
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Altered intestinal permeability has been correlated with Parkinson's pathophysiology in the enteric nervous system, before manifestations in the central nervous system (CNS). The inflammatory endotoxin or lipopolysaccharide (LPS) released by gut bacteria is known to modulate α-synuclein amyloidogenesis through the formation of intermediate nucleating species. Here, biophysical techniques in conjunction with microscopic images revealed the molecular interaction between lipopolysaccharide and α-synuclein that induce rapid nucleation events.

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Subcutaneous insulin delivery serves as the major treatment for the ever-increasing spread of type II diabetes worldwide. However, long-term exposure to insulin results in local aggregates at the site of injection. This therapeutic concern accentuates the need to develop newer effective excipients to stabilize the insulin in pharmaceutical formulations.

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Fluorescence correlation spectroscopy (FCS) is a single-molecule sensitive technique with widespread applications in biophysics. However, conventional microscope-based FCS setups have limitations in performing certain experiments such as those requiring agitations such as stirring or heating, and those involving measurements in solvents with the mismatch of refractive indices. We have recently developed an FCS setup that is suitable for performing measurements inside regular cuvettes.

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We have developed a fluorescence correlation spectroscopy (FCS) setup for performing single-molecule measurements on samples inside regular cuvettes. The cuvette FCS uses a horizontally mounted extra-long working distance, 0.7 NA, air objective with a working distance of >1.

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Transthyretin (TTR) is a homotetrameric protein that is found in the plasma and cerebrospinal fluid. Dissociation of TTR tetramers sets off a downhill cascade of amyloid formation through polymerization of monomeric TTR. Interestingly, TTR has an additional, biologically relevant activity, which pertains to its ability to slow the progression of amyloid beta (Aβ) associated pathology in transgenic mice.

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Amyloids are heterogeneous assemblies of extremely stable fibrillar aggregates of proteins. Although biological activities of the amyloids are dependent on its conformation, quantitative evaluation of heterogeneity of amyloids has been difficult. Here we use disaggregation of the amyloids of tetramethylrhodamine-labeled Aβ (TMR-Aβ) to characterize its stability and heterogeneity.

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Injection of exogenous insulin in the subcutaneous mass has been a proven therapy for type II diabetes. However, chronic administration of insulin often develops local amyloidosis at the injection site, pathologically known as "Insulin Ball". This reduces the insulin bioavailability and exacerbates the disease pathology.

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In aqueous solutions with high concentrations of chemical denaturants such as urea and guanidinium chloride (GdmCl) proteins expand to populate heterogeneous conformational ensembles. These denaturing environments are thought to be good solvents for generic protein sequences because properties of conformational distributions align with those of canonical random coils. Previous studies showed that water is a poor solvent for polypeptide backbones, and therefore, backbones form collapsed globular structures in aqueous solvents.

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Deposition of amyloid-β (Aβ) in Alzheimer's disease (AD) is strongly correlated with the APOE genotype. However, the role of apolipoprotein E (apoE) in Aβ aggregation has remained unclear. Here we have used different apoE preparations, such as recombinant protein or protein isolated from cultured astrocytes, to examine the effect of apoE on the aggregation of both Aβ1-40 and Aβ1-42.

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Emerging paradigms mandate discovery of imaging agents for diagnosing Alzheimer's disease (AD) prior to appearance of clinical symptoms. To accomplish this objective, a novel heterocyclic molecule (4) was synthesized and validated as Aβ targeted probe. The agent shows labeling of numerous diffuse Aβ plaques in confirmed AD human brain tissues and traverses the blood-brain barrier to enable labeling of parenchymal Aβ plaques in live mice (APP(±)/PS1(±)) brains.

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Huntington disease is caused by mutational expansion of the CAG trinucleotide within exon 1 of the huntingtin (Htt) gene. Exon 1 spanning N-terminal fragments (NTFs) of the Htt protein result from aberrant splicing of transcripts of mutant Htt. NTFs typically encompass a polyglutamine tract flanked by an N-terminal 17-residue amphipathic stretch (N17) and a C-terminal 38-residue proline-rich stretch (C38).

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Apolipoprotein E (apoE), first described in 1973, is a truly fascinating protein. While studies initially focused on its role in cholesterol and lipid metabolism, one apoE isoform (apoE4) is a major risk factor for development of late onset Alzheimer's disease. Yet the difference between apoE3, the common form, and apoE4 is a single amino acid of the 299 in this 34 kDa protein.

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Apolipoprotein E gene (APOE) alleles may shift the onset of Alzheimer's disease (AD) through apoE protein isoforms changing the probability of amyloid-β (Aβ) accumulation. It has been proposed that differential physical interactions of apoE isoforms with soluble Aβ (sAβ) in brain fluids influence the metabolism of Aβ, providing a mechanism to account for how APOE influences AD risk. In contrast, we provide clear evidence that apoE and sAβ interactions occur minimally in solution and in the cerebrospinal fluid of human subjects, producing apoE3 and apoE4 isoforms as assessed by multiple biochemical and analytical techniques.

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Although amyloid β (Aβ) is a critical player in the pathology of Alzheimer's disease, there is currently little Information on the rate and extent of formation of oligomers that lead to the presence of Aβ fibrils observed in amyloid plaques. Here we describe a unique method to monitor the full time course of Aβ aggregation. In this method, Aβ is labeled with tetramethylrhodamine at a lysine residue on the N-terminal end.

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Apolipoproteins E3 and E4, proteins with a molecular mass of 34.15 kDa, differ by a single amino acid change. ApoE4 contains an arginine residue at position 112, whereas apoE3 has a cysteine at this position.

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Apolipoprotein E, a 34 kDa protein, plays a key role in triglyceride and cholesterol metabolism. Of the three common isoforms (ApoE2, -3, and -4), only ApoE4 is a risk factor for Alzheimer's disease. All three isoforms of wild-type ApoE self-associate to form oligomers, a process that may have functional consequences.

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The three common isoforms of apolipoprotein E (ApoE) differ at two sites in their 299 amino acid sequence; these differences modulate the structure of ApoE to affect profoundly the isoform associations with disease. The ε4 allele in particular is strongly associated with Alzheimer's disease. The study of the structural effects of these mutation sites in aqueous media is hampered by the aggregation proclivity of each ApoE isoform.

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