Hongbo Yuan

Nucleobase-Functionalized Conjugated Polymer for Detection of Copper(II)

In recent years, supramolecular organization of thiophene derivatives, oligo- and polythiophene, have been developed with various designs to achieve complex functions. Here, we describe the synthesis and characterization of a conjugated polymer with thymidine side chain bases and polythiophene backbones (PTT) instead of phosphate bonds in DNA, and the PTT exhibits exceptional fluorescence quenching efficiency upon binding of Cu(2+) ions in aqueous medium, which is suggested to be electron transfer from the π* orbit at the excited state of PTT to the 3d orbit of Cu(2+) ions and subsequent Cu(2+)-mediated interpolymer π-stacking aggregation. Furthermore, Cu(2+) ions can be selectively and easily monitored by the fluorescence quenching of PTT, which can be used for detection of Cu(2+) ions with good selectivity and high sensitivity in aqueous medium. Both experimental and theoretical methods have been devoted to demonstrate the strong affinity and steric interaction of PTT toward Cu(2+). These findings will illustrate new directions for the design of nucleobase-functionalized materials with transition metals responsive activity.

Divalent Cations Modulate TMEM16A Calcium-Activated Chloride Channels by a Common Mechanism

The gating of Ca2+-activated Cl− channels is controlled by a complex interplay among [Ca2+]i, membrane potential and permeant anions. Besides Ca2+, Ba2+ also can activate both TMEM16A and TMEM16B. This study reports the effects of several divalent cations as regulators of TMEM16A channels stably expressed in HEK293T cells. Among the divalent cations that activate TMEM16A, Ca2+ is most effective, followed by Sr2+ and Ni2+, which have similar affinity, while Mg2+ is ineffective. Zn2+ does not activate TMEM16A but inhibits the Ca2+-activated chloride currents. Maximally effective concentrations of Sr2+ and Ni2+ occluded activation of the TMEM16A current by Ca2+, which suggests that Ca2+, Sr2+ and Ni2+ all regulate the channel by the same mechanism.

Ca2+-controlled assembly for visualized detection of conformation changes of calmodulin.

A new strategy has been designed for visualized detection of the conformation changes of calmodulin bound to target peptide (CaM-M13) based on the conformation sensitive property of a water-soluble conjugated polythiophene derivative (PMNT) and the electrostatic interactions of PMNT/CaM-M13. Interestingly, the direct visualized PMNT color changes under UV irradiation and the turbidity changes of samples in aqueous medium can be applied to detect the conformation changes as well as the controllable assembly of PMNT/CaM-M13 with Ca(2+) in aqueous medium. Because of the specific binding of Ca(2+), the assembly of PMNT/CaM-M13 can be applied to sense calcium as well.

TMEM16A/B Associated CaCC: Structural and Functional Insights

Calcium-activated chloride channels (CaCCs) play fundamental roles in numerous physiological processes. Transmembrane proteins 16A and 16B (TMEM16A/B) were identified to be the best molecular identities of CaCCs to date. This makes molecular investigation of CaCCs become possible. This review discusses the latest findings of TMEM16A/B associated CaCCs, the calcium and voltage dual dependence，the reorganization of Ca(2+)-binding site, the mechanisms of direct or indirect activation, the structure-functional relationship, and the possible stereoscopic structure. TMEM16A and other members of the family are associated with several kinds of cancers and other chloride channelopathies. An understanding of TMEM16 associated channel proteins will shed some light on their role in oncology and in pharmacology development.

Carbon Dioxide‐Controlled Assembly of Water‐Soluble Conjugated Polymers Catalyzed by Carbonic Anhydrase

The CO2 -responsive and biocatalytic assembly based on conjugated polymers has been demonstrated by combining the signal amplification property of the polythiophene derivative (PTP) and the catalytic actions of carbonic anhydrase (CA). CO2 is applied as a new trigger mode to construct the smart assembly by controlling the electrostatic and hydrophobic interactions between the PTP molecules in aqueous solution, leading to the visible fluorescence changes. Importantly, the assembly transformation of PTP can be specifically and highly accelerated by CA based on the efficient catalytic activity of CA for the inter-conversion between CO2 and HCO3- , mimicking the CO2 -associated biological processes that occurred naturally in living organisms. Moreover, the PTP-based assembly can be applied for biomimetic CO2 sequestration with fluorescence monitoring in the presence of CA and calcium.

Conjugated Polyelectrolyte-Based New Strategy for in Situ Detection of Carbon Dioxide

A conjugated polymer centered on fluorene and 2,1,3-benzothia-diazole (PFBT) is prepared for sensing CO2 in situ with high sensitivity and low background. Upon introducing CO2, the weaker electrostatic repulsion and stronger hydrophobic interactions between neighboring PFBT molecules enhance the interchain contacts compared to that without CO2, leading to the energy transfer from fluorene to 2,1,3-benzothia-diazole sites and the emission color shift from blue to green, which is sensitive to sensing CO2 in atmospheric air with a content of ∼400 ppm. Importantly, PFBT is employed to monitor photosynthesis and respiration upon cycling day and night in situ.

A Multiple-Stimulus-Responsive Biomimetic Assembly Based on a Polyisocyanopeptide and Conjugated Polymer

An assembly was fabricated and was revealed to be a multiple-stimulus-responsive biomimetic hybrid polymer architecture. It was constructed by the hydrophobic interactions between a conjugated polyfluorene that contained 2,1,3-benzothiadiazole units (PFBT) and a tri(ethylene glycol)-functionalized polyisocyanopeptide (3OEG-PIC). The introduction of PFBT to the polyisocyanopeptide (PIC) network allowed for the incorporation of responsiveness to multiple stimuli including temperature, CO2 , carbonic anhydrase, and nonlinear mechanics, which mimics natural processes and interactions. Furthermore, the light-harvesting and signal amplification characteristics of PFBT endowed the supramolecular assembly with the essential function of fluorescence monitoring for biological processes.

Molecular simulation assisted identification of Ca2+ binding residues in TMEM16A

Calcium-activated chloride channels (CaCCs) play vital roles in a variety of physiological processes. Transmembrane protein 16A (TMEM16A) has been confirmed as the molecular counterpart of CaCCs which greatly pushes the molecular insights of CaCCs forward. However, the detailed mechanism of Ca2+ binding and activating the channel is still obscure. Here, we utilized a combination of computational and electrophysiological approaches to discern the molecular mechanism by which Ca2+ regulates the gating of TMEM16A channels. The simulation results show that the first intracellular loop serves as a Ca2+ binding site including D439, E444 and E447. The experimental results indicate that a novel residue, E447, plays key role in Ca2+ binding. Compared with WT TMEM16A, E447Y produces a 30-fold increase in EC50 of Ca2+ activation and leads to a 100-fold increase in Ca2+ concentrations that is needed to fully activate the channel. The following steered molecular dynamic (SMD) simulation data suggests that the mutations at 447 reduce the Ca2+ dissociation energy. Our results indicated that both the electrical property and the size of the side-chain at residue 447 have significant effects on Ca2+ dependent gating of TMEM16A.

Remote‐Controlling Potassium Channels in Living Cells through Photothermal Inactivation of Calmodulin

Spatiotemporal regulation of cellular functions provides a powerful strategy for understanding underlying mechanisms of cellular bioprocesses. Here, a strategy is reported to realize the remote control of the activities of potassium channels via photothermal inactivation of calmodulin (CaM) by using reduced graphene oxide decorated with calmodulin binding peptide (rGO-P) as the transducer with near-infrared light (NIR) irradiation. Upon NIR light irradiation, the CaM/Ca2+ bound to rGO-P is inactivated by the photothermal effect of rGO-P, resulting in the incapability of binding with Ca2+ . Hence, the closed Kv10.1 channel is converted to be open in the presence of calcium in living cells. Meanwhile, the SK2 channel is induced to be closed from the open state and the Kir2.1 channel is unaffected by the intracellular inactivation of CaM. This strategy gives a noninvasive and effective approach to remotely control the activities of potassium channels, offering an alternative for the development of optogenetics.