[Expression of Ietalurus punetaus β-defensin based on recombinant Pichia pastoris].

β-defensin is a primary protein immune factor in channel catfish's (Ietalurus punetaus) resistance to pathogenic microorganisms. Its primary structure contains a signal peptide composed of 24 amino acid residues at the N-terminal and a mature peptide composed of 43 amino acid residues at the C-terminal. The mature peptide region is responsible for the biological activity of β-defensin. In the present study, a recombinant strain of Pichia pastoris that produces channel catfish β-defensin, was constructed to realize the biosynthesis of channel catfish β-defensin based on eukaryotic expression. First, the β-defensin gene "IPBD" was isolated from the skin of channel catfish by RT-PCR. After linking it with the expression vector pPICZA, pPICZA-IPBD was transferred into competent P. pastoris X-33 cells to obtain recombinant P. pastoris strains. The yeast transformants with multi-copy gene inserts were obtained by using the culture medium containing 1 000 μg/mL zeocin. Using BMM culture medium (without amino nitrogen culture medium) instead of BMMY culture medium (with amino nitrogen culture medium), the fermentation and culture conditions of the recombinant strain were optimized, and the optimal conditions for producing channel catfish β-defensin were determined as follows: the expression was induced for 96 h with 1.0% methanol at 28 °C , 250 r/min. Purified protein with molecular weight of 5.98 kDa was obtained by nickel affinity chromatography, and MALDI-TOF/TOF mass spectrometry proved that it was the expected recombinant IPBD. The antibacterial test results showed that the inhibitory rates of recombinant IPBD on Gram-positive Staphylococcus aureus and Listeria monocytogenes and Gram-negative Pseudomonas aeruginosa were 69.6%, 71.6% and 65.8%, respectively. This study provides a recombinant DNA technique for the development of small molecule natural antibacterial peptide from fish.β-防御素是斑点叉尾鮰Ietalurus punetaus 抵御病原微生物侵染的首要蛋白质免疫因子，其一级结构包含氨基端24 个氨基酸组成的信号肽和羧基端43 个氨基酸组成的成熟肽，该成熟肽赋予β-防御素的生物学活性。文中首次构建了产斑点叉尾鮰β-防御素的毕赤酵母Pichia pastoris 重组菌株，实现了基于真核表达的斑点叉尾鮰β-防御素的生物合成。首先通过RT-PCR 从斑点叉尾鮰皮肤中分离β-防御素成熟肽基因“IPBD”，将其与表达载体pPICZαA连接并转入毕赤酵母X-33 后，获得重组毕赤酵母菌株；经含1 000 μg/mL 博来霉素的培养基筛选，获得高拷贝重组菌株。以BMM 培养基 (无氨基氮源培养基) 替代BMMY 培养基 (含氨基氮源培养基)，对重组菌株的发酵培养条件进行优化，确定其产斑点叉尾鮰β-防御素的最适条件为：28 ℃、250 r/min、1.0%甲醇诱导表达96 h。重组菌株产物经镍离子亲和层析获得分子量为5.98 kDa 的纯化蛋白，基于MALDI-TOF-TOF 的质谱分析证明该纯化蛋白为重组IPBD。抑菌活性测定结果表明重组IPBD 对革兰氏阳性的金黄色葡萄球菌Staphylococcus aureus、单增李斯特菌Listeria monocytogenes 以及革兰氏阴性的铜绿假单胞菌Pseudomonas aeruginosa 的抑菌率分别为69.6%、71.6%和65.8%。本研究为鱼类来源天然小分子抗菌肽的开发提供了可参考的重组DNA 技术。.