OBJECTIVE: To investigate antagonistic activities of three isomers of α-conotoxin TxIB on rat and human α6 /α3β2β3 nicotinic acetylcholine receptors (nAChRs). METHODS: Three disulfide bond isomers were synthesized using Fmoc chemistry, which were identified by ultra performance liquid chromatography (UPLC)and confirmed by MALDI-TOF mass spectrometry. Rat and human α6/α3β2β3 nAChRs were expressed in oocytes of Xenopus laevis, which were used to test the antagonistic abilities of the 3 isomers. RESULTS: The three isomers of α-conotoxin TxIB were synthesized successfully. The retention time of each isomer of α-conotoxin TxIB was different each other significantly. The observed molecular masses of three isomers were the same, which were consistent with their theoretical molecular mass. Their hydrophilicity orders were globular > ribbon > bead. Both rat and human α6/α3β2β3 nAChRs were expressed in oocytes well. Inhibition of three isomers of α-conotoxin TxIB on rat and human α6 /α3β2β3 nAChRs were evaluated respectively. Among the three isomers of TxIB, the activity of the globular isomer was the most potent one, which had almost same activity at rat and human α6/α3β2β3 nAChRs with corresponding IC50 of 28.2 and 32.0 nmol·L-1 respectively. However, the other two isomers, ribbon and bead isomers displayed little antagonistic effect on both rat and human α6/α3β2β3 nAChRs only with an IC50 of > 10 μmol·L-1. CONCLUSION: The synthesized globular isomer of α-conotoxin TxIB in this work has a high selectivity and potent antagonistic activity on rat and human α6/α3β2β3 nAChRs, which would be helpful for its new drug development.

OBJECTIVE: To interrogate differential sensitivity of α-conotoxin TxID on stoichiometry of α3β4 nicotinic acetylcholine receptors(nAChRs). METHODS: Oocytes of Xenopus laevis were used to express rat α3β4 nAChRs with different stoichiometries by altering α3:β4 RNA injection ratios of 1:1, 1:10 or 10:1. Sensitivity of α-conotoxin TxID on these different stoichiometry receptors were evaluated and compared. RESULTS: The three stoichiometry receptors of α3β4 nAChRs were expressed in oocytes successfully. α-Conotoxin TxID showed differential sensitivity on α3β4 nAChR stoichiometries. Inhibition of 1:10 injection ratio by TxID was similar with regular 1:1 α3β4 nAChRs within 2-fold difference. While potency of 10:1 injection ratio by TxID decreased 5-fold significantly comparing with 1:1 α3β4 nAChRs. CONCLUSION: α-Conotoxin TxID exhibits distinct sensitivity on different stoichiometry of α3β4 nAChRs, which could reflecting different stoichiometries of α and β subunits. The RESULTS would be helpful for elucidation of structure and physiology function of α3β4 nAChRs.

Nicotinic acetylcholine receptors (nAChRs) belong to ligand-gated ion channel receptors, of which α7 nAChR subtype is widely distributed in the cerebral cortex, thalamus, hippocampus, and also identified in microglia, macrophages, bone marrow cells, etc. Previous studies revealed that α7 nAChR is closely related to the function of the cholinergic anti-inflammatory pathway, and is a vital target for drug development of Alzheimer's disease and schizophrenia. The establishment of a stable α7 nAChR in vitro drug screening system is crucial for the efficient screening of novel drugs targeting this target. Recombinant expression of different subtypes of nAChRs on Xenopus laevis oocyte membranes and current detected by two-electrode voltage clamp (TEVC) is an advanced and complex model for novel drug screening. Molecular chaperones can assist the assembly of some nAChR subunits to form functional receptors, providing a stable expression model for the screening of compounds targeting this receptor. In this study, a molecular chaperone gene of α7 nAChR, transmembrane protein 35A (Tmem35a), was isolated and cloned from rats. We constructed the recombinant expression vector and obtained the cRNA of Tmem35a by in vitro transcription technique. Two cRNAs (Tmem35a and α7) were mixed and injected into X. laevis oocytes for expression. Then, the effects of this molecular chaperone on the current expression and pharmacological properties of α7 nAChR were evaluated by the TEVC. The results revealed that TMEM35A, also known as novel acetylcholine receptor chaperone (NACHO) could effectively increase the expression of α7 nAChR protein on oocyte membranes, and the amount of α7 nAChR protein was increased about 1-fold. The peak current induced by agonist acetylcholine (ACh) was increased about 10-fold. After injection of Tmem35a cRNA, the median effect concentration (EC₅₀) value of α7 nAChR to agonist ACh is 228.5 μmol·L^-1, which shows almost no difference from native α7 nAChR (EC₅₀: 223.3 μmol·L^-1), indicating the preservation of the normal properties of α7 nAChR. The results of this investigation indicate that the molecular chaperone NACHO effectively assists the heterologous expression of α7 nAChR in X. laevis oocytes, which provides a model for screening the potency of lead compounds targeting α7 nAChR. All animal experiments in this study were reviewed and approved by the Ethics Committee of Guangxi University (approval number: GXU-2023-0249).

N-type voltage-gated calcium (Ca²⁺) channels (N-type VGCC, Ca_V2.2) mediate Ca²⁺ influx in response to action potential at the presynaptic terminal, and play an important role in synaptogenesis, neurotransmitter release and nociceptive signal transduction. It is a new target for the development of drugs for the treatment of neuralgia (chronic pain) and other major diseases. Due to the difficulty of calcium channel expression in vitro and the detection of channel current, there is a great lack of new drug screening models. In this study, we established and optimized the electrophysiological drug screening model using Xenopus laevis oocytes for the recombinant expression of Ca_V2.2 in vitro (this study were reviewed and approved by the Ethics Committee of Guangxi University, approval number: GXU-2023-0249). Firstly, the linear plasmids encoding cDNA of major subunit α1B and auxiliary subunits α2δ1 and β3 of rat Ca_V2.2 were used as templates for in vitro transcription to generate their related mRNA (cRNA), after which three kinds of cRNA were injected into Xenopus laevis oocytes at the mass ratio of 2∶1∶1 for expression. The two-electrode voltage clamp (TEVC) technique was used to detect the inward current produced by Ca_V2.2. At the same time, the expression conditions of Ca_V2.2 were optimized, and its gating function was characterized from the aspects of channel activation and inactivation. The results showed that 3-5 days after cRNA microinjection, stable Ca_V2.2-mediated barium ion (Ba²⁺) currents were successfully detected. The interference of endogenous potassium channels and Ca²⁺-activated chloride channels can be eliminated by tetraethylammonium hydroxide (TEAOH) and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (BAPTA-AM) treatment. The maximum potential for Ca_V2.2 activation is 0 mV, and the current reverses to be outward when the membrane potential is greater than +50 mV. By fitting the steady-state activation and inactivation curves, the half-maximal activation potential and half-maximal inactivation potential of Ca_V2.2 are identified as -15.9 and -60.2 mV. In this study, a stable Ca_V2.2 expression system was established based on Xenopus laevis oocytes. The in vitro expression system can provide a new way for the screening of Ca_V2.2 active compounds or lead drugs.

The cyanuric chloride linkers have been used for cyclizing polypeptide, but not used for α-conotoxin, the peptides with rich disulfide bonds and more amino acid residues. In this study, cyclic peptides c[A10L]PnIA-1-4 were synthesized efficiently by lysine assisted cyanuric chloride linkers with 28.92%-52.00% yields. The activity evaluation showed that the IC₅₀ values of c[A10L]PnIA-1 against α7 and α3β2 nAChR subtypes were 5 and 7 times higher than [A10L]PnIA respectively, and the subtype selectivity was maintained. The results of circular dichroism show that this cyclization method had no significant effect on its secondary structure. Compared with the commonly used head-to-tail cyclization in conotoxin cyclization, this method has the advantages of rapid reaction and high yield, which is expected to be further applied to the cyclization study of various α-conotoxins.

The α-conotoxins are peptide toxins that are identified from the venom of marine cone snails and they hold outstanding potency on various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs have an important role in regulating transmitter release, cell excitability, and neuronal integration, so nAChR dysfunctions have been involved in a variety of severe pathologies. Four types of α-3/5 conotoxins MI, MIA, MIB and MIC have been found from Conus magus. Among them, the activity and selectivity of MIA and MIB have not been well studied. In this study, four α-3/5 conotoxins MI, MIA, MIB and MIC were synthesized by solid peptide synthesis method, and the bioactivities of them were screened by double electrode voltage clamp electrophysiology. The results showed that MIA and MIB selectively inhibited muscle type acetylcholine receptors with IC₅₀ values of 14.45 and 72.78 nmol·L^-1, respectively, which are slightly weaker than MI and MIC. Molecular docking results have shown MIA and MIB interact with muscle-type nAChRs with similar mechanism. The reasons for activity differences may relate to the size of the N-terminal amino acids. Together, the conotoxins MIA and MIB may have the potential to develop as a tool for detect the function of muscle type nAChRs, as well as the diagnosis or treat of related diseases.

italic>α7 nicotinic acetylcholine receptor (nAChR) is widely distributed in the central and peripheral nervous systems, and is closely related to a variety of neurological diseases and inflammation response. α-Conotoxin [A10L]PnIA, as an antagonist targeting α7 nAChR, plays an important role in studying the physiological and pathological processes involved in α7 nAChR. [A10L]PnIA was labeled with fluorescein 5-carboxytetramethylrhodamine, and the active peptide ([A10L]PnIA-F) was obtained by a two-step oxidative folding procedure in vitro. The Xenopus oocyte expression system and the two-electrode voltage clamp technique were used to identify the potency of [A10L]PnIA-F fluorescent peptide, and its cytotoxicity was detected by mouse macrophages and CCK8 method. The molecular weight of [A10L]PnIA-F fluorescent peptide was identified by mass spectrometry as 2 077.28 Da, which was consistent with the theoretical value. Electrophysiological determination of its half-maximal inhibitory concentration (IC₅₀) for α7 nAChR is 17.32 nmol·L^-1, which is consistent with [A10L]PnIA (IC₅₀, 13.84 nmol·L^-1). The cytotoxicity test results showed that within the concentration range of 5 nmol·L^-1 to 10 μmol·L^-1, there was no significant inhibition on the growth of mouse macrophages. The results showed that the α-conotoxin fluorescent probe [A10L]PnIA could provide pharmacological tools for the research of α7 nAChR-related neurophysiological and pathological mechanisms.