力生长因子在大肠杆菌中的表达及活性分析

MGF(Mechano-growth factor)是一种IGF-1变体形式, 研究发现该因子具有应力敏感性, 并且具有促进肌肉肥大、再生以及神经损伤修复的功能。通过RT-PCR从拉伸刺激的人成骨细胞中克隆MGF cDNA序列, 并去除5'端9 bp的序列, 使N端缺少对肠激酶(Enterokinase, EK)具有抑制作用的脯氨酸, 将截短型MGF (des(1-3) MGF) cDNA序列克隆入pET32a(+)质粒, 构建重组表达质粒。重组质粒转化E. coli BL21(DE3), 在30oC培养下以可溶形式表达融合蛋白Trx/ des(1-3)MGF, 采用离子交换层析和Ni2+金属亲和层析, 获得纯度95%以上的融合蛋白。再对融合蛋白EK酶切, rpHPLC分离获得纯度达98%的des(1-3)MGF, SDS-PAGE电泳及质谱分析蛋白分子量与理论值相符。生物活性实验显示, 所制备的des(1-3)MGF比des(1-3)IGF-1更显著的促进MC3T3-E1细胞的增值和迁移。

Expression of Mechano-growth Factor in Escherichia coli and Activity Analysis

Mechano-growth factor (MGF) is one of IGF-1 isoforms. MGF is mechanosensitive and has important functions in muscle hypertrophy, regeneration and nerve injury recovery. In this study, MGF cDNA (330 bp) was cloned from stretched osteoblasts by RT-PCR. In order to avoid prolin residue inhibiting enterokinase cleavage, 9bp of MGF cDNA 5' end sequence was truncated by primer, then the obtained truncated MGF (des(1-3)MGF) cDNA (321 bp) was subcloned in pET32a(+) vector to construct a prokaryotic recombination expression plasmid. Trx/des(1-3)MGF fusion protein, existing in forms of solution, was expressed in transformed Escherichia coli strain BL21(DE3) by IPTG induction at 30 degres C. The supernatant of cell lysates was subjected to ion exchange chromatography and Ni2+ metal affinity chromatography, and the fusion protein was obtained with the purity over 95%. After the fusion protein was cleaved by enterokinase, Trx and des(1-3)MGF was isolated by reverse-phase HPLC. Through these procedures, des(1-3) MGF was obtained with the purity of 98%. The protein molecular mass was conformity to the theoretical value by SDS-PAGE and mass spectrometry analysis. The purified des(1-3)MGF was incubated with MC3T3-E1 for cell proliferation and migration assays. The results show that des(1-3)MGF exhibited more facilitative effects on proliferation and migration of MC3T3-E1 than that of des(1-3)IGF-1.