Valiyaveetil Francis I, MacKinnon Roderick, Muir Tom W
Howard Hughes Medical Institute, The Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, New York, New York 10021, USA.
J Am Chem Soc. 2002 Aug 7;124(31):9113-20. doi: 10.1021/ja0266722.
In this contribution we describe the semisynthesis of the potassium channel, KcsA. A truncated form of KcsA, comprising the first 125 amino acids of the 160-amino acid protein, was synthesized using expressed protein ligation. This truncated form corresponds to the entire membrane-spanning region of the protein and is similar to the construct previously used in crystallographic studies on the KcsA protein. The ligation reaction was carried out using an N-terminal recombinant peptide alpha-thioester, corresponding to residues 1-73 of KcsA, and a synthetic C-terminal peptide corresponding to residues 74-125. Chemical synthesis of the C-peptide was accomplished by optimized Boc-SPPS techniques. A dual fusion strategy, involving glutathione-S-transferase (GST) and the GyrA intein, was developed for recombinant expression of the N-peptide alpha-thioester. The fusion protein, expressed in the insoluble form as inclusion bodies, was refolded and then cleaved successively to remove the GST tag and the intein, thereby releasing the N-peptide alpha-thioester. Following chemical ligation, the KcsA polypeptide was folded into the tetrameric state by incorporation into lipid vesicles. The correctness of the folded state was verified by the ability of the KcsA tetramer to bind to agitoxin-2. To our knowledge, this work represents the first reported semisynthesis of a polytopic membrane protein and highlights the potential application of native chemical ligation and expressed protein ligation for the (semi)synthesis of integral membrane proteins.
在本论文中，我们描述了钾通道KcsA的半合成。使用表达蛋白连接法合成了KcsA的截短形式，该形式包含160个氨基酸的蛋白质的前125个氨基酸。这种截短形式对应于该蛋白质的整个跨膜区域，并且类似于先前用于KcsA蛋白晶体学研究的构建体。连接反应使用对应于KcsA的1-73位残基的N端重组肽α-硫酯和对应于74-125位残基的合成C端肽进行。C肽的化学合成通过优化的Boc-SPPS技术完成。开发了一种涉及谷胱甘肽-S-转移酶（GST）和GyrA内含肽的双重融合策略，用于N肽α-硫酯的重组表达。以不溶性形式作为包涵体表达的融合蛋白被重折叠，然后依次切割以去除GST标签和内含肽，从而释放N肽α-硫酯。化学连接后，通过将KcsA多肽掺入脂质囊泡中使其折叠成四聚体状态。通过KcsA四聚体与阿吉毒素-2结合的能力验证了折叠状态的正确性。据我们所知，这项工作代表了首次报道的多跨膜蛋白的半合成，并突出了天然化学连接和表达蛋白连接在整合膜蛋白（半）合成中的潜在应用。
