Biology subjects

Sahoo, B.

Publications and source records attributed to Sahoo, B..

24 records · Page 2Linked to original sources

bioRxiv2018

Self-assembly of polymer-encased lipid nanodiscs and membrane protein reconstitution

The absence of detergent and curvature makes nanodiscs to be excellent membrane mimetics. The lack of structural and mechanistic model of polymer-encapsulated lipid-nanodiscs limits their use to study the structure, dynamics and function of membrane proteins. In this study, we parametrized and optimized the coarse-graining (CG) bead-mapping for two differently charged and functionalized copolymers, namely styrene-maleic acid (SMAEA) and polymethacrylate (PMAQA), for the Martini force-field framework and showed nanodisc formation (< 8 nm diameter) on a time scale of tens of microseconds using molecular dynamics (MD) simulation. Structural models of ~ 2.0 or 4.8 kDa PMAQA and ~2.2 kDa SMAEA polymer based lipid-nanodiscs highlights the importance of polymer chemical structure, size and polymer:lipid molar ratio in the optimization of nanodisc structure. The ideal spatial arrangement of polymers in nanodisc, nanodisc size and thermal stability obtained from our MD simulation correlates well with the experimental observations. The polymer-nanodisc were tested for the reconstitution of single-pass or multi-pass transmembrane proteins. We expect this study to be useful in the development of novel polymer based lipid-nanodiscs and for the structural studies of membrane proteins. TOC GRAPHICS O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/476556v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@ae71c6org.highwire.dtl.DTLVardef@af961borg.highwire.dtl.DTLVardef@1a7e6c3org.highwire.dtl.DTLVardef@1f4a9a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2018

Alzheimer’s Amyloid-Beta Intermediates Generated by Polymer-Nanodiscs

Polymethacrylate-copolymer (PMA) encased lipid-nanodiscs (~10 nm) and macro-nanodiscs (>15 nm) are used to study A{beta}1-40 aggregation. We demonstrate that PMA-nanodiscs form a ternary association with A{beta} and regulate its aggregation kinetics by trapping intermediates. Results demonstrating reduced neurotoxicity of nanodisc-bound A{beta} oligomers are also reported.

biophysics↗

bioRxiv2018

Zinc Boosts EGCG’s hIAPP Amyloid Inhibition Both in Solution and Membrane

Amyloid aggregation of human islet amyloid polypeptide (hIAPP) is linked to insulin-producing islet cell death in type II diabetes. Previous studies have shown the amyloid inhibiting effects of zinc (Zn) and insulin that are co-present with hIAPP in islet cells, and the lipid membrane has been shown to significantly influence the aggregation kinetics. Increasing number of studies report the importance of developing small molecule inhibitors to suppress the hIAPPs toxicity. Particularly, the ability of epigallocatechin-gallate (EGCG) to inhibit amyloid aggregation of a variety of amyloid peptide/proteins including hIAPP initiated numerous studies including the development of compounds to potentially treat amyloid diseases. In this study, by using a combination of thioflavin-T fluorescence and transmission electron microscopy experiments, we demonstrate a significant enhancement in EGCGs efficiency, when mixed with Zn, to significantly suppress hIAPP amyloid aggregation both in presence and absence of lipid membrane. Circular dichroism experiments indicate the formation and stabilization of a helical structure of hIAPP in presence of EGCG:Zn complex. Our results also reveal the ability of EGCG or EGCG:Zn to suppress hIAPPs cellular toxicity and that the ability of EGCG to chelate with Zn suppresses zincs cellular toxicity. We suggest that the reported results would be useful to develop strategies to trap hIAPP intermediates for further biophysical and structural studies, and also to devise approaches to abolish amyloid aggregation and cellular toxicity.

biophysics↗

bioRxiv2018

Cationic polymethacrylate-copolymer acts as an agonist for beta-amyloid and antagonist for amylin fibrillation

In human, amyloid-beta (A{beta}) and islet amyloid polypeptide (hIAPP) aggregations are linked to Alzheimers disease and Type-2 Diabetes, respectively. There is significant interest in better understanding the aggregation process by using chemical tools. Here, we show the ability of a cationic polymethacrylate-copolymer (PMAQA) to quickly induce {beta}-hairpin structure and promote fibrillation in A{beta}40, and to constrain the conformational plasticity of hIAPP for several days and inhibit its aggregation at sub-micromolar concentrations. NMR experiments and atomistic molecular dynamics simulations reveal that PMAQA electrostatically interacts with A{beta}40s Glu22 and Asp23 followed by {beta}-sheet induction while it binds strongly to the closest proximity of amyloid core domain (NFGAIL) of hIAPP and restrain its structural rearrangement. This study provides a valuable approach to develop polymer-based anti-amyloid inhibitors that may diminish the population of intermediates of A{beta}40 or hIAPP.

biophysics↗

bioRxiv2018

ERBB2 and KRAS Alterations Mediate Response to EGFR Inhibitors in early stage Gallbladder Cancer

The uncommonness of gallbladder cancer has contributed to the generally poor understanding of the disease, with scant reports restricted to advance-stage tumors. Here, using an integrated analysis of whole exome and phospho-proteome, we show recurrent activating ERBB2 and KRAS somatic mutations are present in 6 and 3 of 44 early-stage rare gallbladder tumors, respectively. In vitro and in vivo cell-based and biochemical assays reveal an essential role of ErbB pathway activation for the survival of gallbladder cells. Interestingly, the genetic and pharmacological dependencies of gallbladder cells are dependent on the KRAS mutant allele status, reminiscent of the clinical algorithm commonly practiced to opt for anti-EGFR treatment in colorectal cancer. In overall, we present the first evidence that the presence of KRAS (G12V), but not KRAS (G13D) mutation, may preclude gallbladder cancer patients to respond to anti-EGFR treatment, leading to an early adoption of an approved treatment regimen for gallbladder cancer patients.

cancer biology↗

bioRxiv2018

A fluorescence correlation spectrometer for measurements in cuvettes

We have developed a fluorescence correlation spectroscopy (FCS) setup for performing single molecule measurements on samples inside regular cuvettes. We built this by using an Extra Long Working Distance (ELWD), 0.7 NA, air objective with working distance > 1.8 mm. We have achieved counts per molecule > 44 kHz, diffusion time < 64 s for rhodamine B in aqueous buffer and a confocal volume < 2 fl. The cuvette-FCS can be used for measurements over a wide range of temperature that is beyond the range permitted in the microscope-based FCS. Finally, we demonstrate that cuvette-FCS can be coupled to automatic titrators to study urea dependent unfolding of proteins with unprecedented accuracy. The ease of use and compatibility with various accessories will enable applications of cuvette-FCS in the experiments that are regularly performed in fluorimeters but are generally avoided in microscope-based FCS.

biophysics↗