Conformational equilibria of curcumin, a potential therapeutic agent, can be modulated by changing pH, temperature and solvent composition.

No abstract

Allostery can be manifested as a combination of repression and activation in multidomain proteins allowing for fine tuning of regulatory mechanisms. Here we have used single molecule fluorescence resonance energy transfer (smFRET) and molecular dynamics simulations to study the mechanism of allostery underlying negative cooperativity between the two agonists glutamate and glycine in the NMDA receptor. These data show that binding of one agonist leads to conformational flexibility and an increase in conformational spread at the second agonist site. Mutational and cross-linking studies show that the dimer–dimer interface at the agonist-binding domain mediates the allostery underlying the negative cooperativity. smFRET on the transmembrane segments shows that they are tightly coupled in the unliganded and single agonist-bound form and only upon binding both agonists the transmembrane domain explores looser packing which would facilitate activation.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that has been associated with the deposition of aggregates of superoxide dismutase 1 (SOD1). Effective therapeutics against SOD1 fibrillation is still an area of active research. Herein, we demonstrate the potential of two naturally occurring flavonoids (quercetin and baicalein) to inhibit fibrillation of wild-type SOD1 with the aid of a series of biophysical techniques. Our seeding experiments reveal that both of these flavonoids significantly affect the fibril elongation. Interestingly, our ThT binding assay, TEM, and SDS-PAGE experiments suggest that these flavonoids also disintegrate the fibrils into shorter fragments but do not completely depolymerize them into monomers. Binding parameters obtained from the analysis of UV−vis spectra suggest that these flavonoids bind moderately to native SOD1 dimer and have different binding sites. Docking of these flavonoids with a non-native monomer, non-native trimer, and oligomer derived from the 11-residue segment of SOD1 indicates that both quercetin and baicalein can bind to these species and thus can arrest the elongation of fibrils by blocking the fibrillar core regions on the intermediate species formed during aggregation of SOD1. MTT assay data revealed that both the flavonoids reduced the cytotoxicity of SOD1 fibrils. Experimental data also show the antiamyloidogenic potential of both flavonoids against A4V SOD1 mutant fibrillation. Thus, our findings may provide a direction for designing effective therapeutic agents against ALS which can act as promising antiamyloidogenic and fibril destabilizing agents.

Zn 21 has been shown to have a wide range of modulatory effects on neuronal AMPARs. However, the mechanism of modulation is largely unknown. Here we show that Zn 21 inhibits GluA2(Q) homomeric receptors in an activity-and voltage-dependent manner, indicating a pore block mechanism. The rate of inhibition is slow, in the hundreds of milliseconds at millimolar Zn 21 concentrations; hence, the inhibition is only observed in the residual nondesensitizing currents. Consequently, the inhibition is higher for GluA2 receptors in complex with auxiliary subunits c2 and c8 where the residual activation is larger. The extent of inhibition is also dependent on charge at site 607, the site that undergoes RNA editing in GluA2 subunits replacing glutamine to arginine, with the percent inhibition being lower and IC 50 being higher for the edited GluA2(R) relative to unedited GluA2(Q) and to GluA2(Q607E), a mutation observed in the genetic screen of a patient exhibiting developmental delays. We also show that Zn 21 inhibition is significant during rapid repetitive activity with pulses of millimolar concentrations of glutamate in both receptors expressed in HEK cells as well as in native receptors in cortical neurons of C57BL/6J mice of either sex, indicating a physiological relevance of this inhibition.