Conopeptide Vt3.1 is a disulfide-cross-linked dimer identified from Conus vitulinus, characterized by its unique structure and preferential inhibition of BK potassium channels containing the β4 subunit. The peptide modulates channel activity by altering voltage-dependent gating, shifting the conductance-voltage relation by approximately 45 mV and reducing maximal conductance by up to 71%. Vt3.1 interacts with acidic residues in the extracellular loops of both the slo1 and β4 subunits via electrostatic interactions, highlighting a large interaction surface between these subunits. This specificity makes Vt3.1 a valuable tool for studying the structural and functional properties of BK channels, particularly those involving the β4 subunit.

Structurally, Vt3.1 lacks ordered secondary elements but adopts an L-shaped conformation with positively charged N-termini that facilitate its interaction with the channel. Unlike pore-blocking toxins, Vt3.1 influences voltage sensor movements and the coupling between voltage sensors and the pore, leading to altered activation kinetics. Its effects are rapid and reversible, further underscoring its utility in probing BK channel dynamics. The peptide's selectivity for β4-containing channels, which are predominantly expressed in neuronal tissues, provides insights into the role of auxiliary subunits in modulating BK channel function.

• Li M, Chang S, Yang L, Shi J, McFarland K, Yang X, Moller A, Wang C, Zou X, Chi C, Cui J. Conopeptide Vt3.1 preferentially inhibits BK potassium channels containing β4 subunits via electrostatic interactions. J Biol Chem. 2014 Feb 21;289(8):4735-42. doi: 10.1074/jbc.M113.535898. Epub 2014 Jan 7. PMID: 24398688; PMCID: PMC3931035.
• Wu XC, Zhou M, Peng C, Shao XX, Guo ZY, Chi CW. Novel conopeptides in a form of disulfide-crosslinked dimer. Peptides. 2010 Jun;31(6):1001-6. doi: 10.1016/j.peptides.2010.03.010. Epub 2010 Mar 20. PMID: 20307606.

三氟乙酸（Trifluoroacetic acid，简称 TFA）是高效液相色谱（简称 HPLC）纯化过程中常用的反离子。TFA 的存在可能会对肽的净重量、外观及溶解度产生影响，具体如下：

对净重量的影响：TFA 盐会增加产物的总质量。在大多数情况下，肽的含量占总重量的 80% 以上，剩余部分则为 TFA。

对溶解度的影响：TFA 盐通常能提高肽在水溶液中的溶解度。

在生物检测中的影响：对于大多数标准的体外检测，残留的 TFA 水平一般不会造成干扰。但需注意，在高灵敏度的细胞研究或生化研究中，需关注其存在可能带来的影响。

干品多肽的重量中不仅仅包含多肽，还包含有一些非肽的组份，如水、被吸收的溶剂、配位离子和盐等。肽的净含量是指肽在其中的重量百分比，这个百分比的数值范围很大，可能从50%到90%，取决于纯度、序列以及合成和纯化的方法，不要将肽的净含量和肽的纯度混为一谈，他们是两个完全不同的概念。纯度通常是通过HPLC测定的。纯度定义的是多肽样品中含正确序列的组分的百分比，而肽的净含量是指样品中肽类物质相对于总物质所占的百分比，肽的净含量通常是氨基酸组分分析或紫外分光法测定的，这个信息主要是在一些对肽的浓度很敏感的实验中，对计算肽的浓度是很重要的。