Affinity purification of phosphacan core protein expressed in Escherichia coli as histidine-tagged fusion protein

Specific regions of core protein of phosphacan, one of the chondroitin sulfate proteoglycans, were expressed as fusion proteins with histidine-tag (His-tag) in Escherichia coli (E.coli) and were affinity purified using nickel-nitrilotriacetic acid (Ni-NTA) matrix. cDNA fragments encoding amino acid residues 343-446 (P3) and 1-340 (P4) of phosphacan core protein were amplified by polymerase chain reaction from E18 rat brain mRNA as template. The amplified products were subcloned into pQE30 vector and were introduced into E.coli strain M15 [pREP4] for the expression. The His-tagged fusion proteins were expressed by cultivating the transformants at 37℃ for 5h in the presence of 1mM IPTG. His-tagged P3 fusion protein (His-P3) was expressed as soluble form, and was purified using Ni-NTA matrix. His-tagged P4 fusion protein (His-P4) which was sequestered into insoluble inclusion bodies was treated with 8.0M urea to solubilize, and then was purified under denaturing conditions.

コンドロイチン硫酸プロテオグリカンの一つであるホスファカンのコア蛋白の特定領域を,ヒスチジンタグ(His-tag)を持つ融合蛋白として大腸菌内で発現させニッケル-ニトリロ3酢酸(Ni-NTA)アフィニティ担体を用いて精製した｡ホスファカンコア蛋白のアミノ酸残基343-446(P3)及び1-340(P4)に相当するcDNA断片を,胎性18日目のラット脳由来のmRNAを鋳型としたPCRによって増幅した｡増幅された断片は発現ベクターpQE30に組み込まれ,これで大腸菌(M15[pREP4])を形質転換した｡His-tag融合蛋白の発現は形質転換株を1mM IPTG存在下で37℃,5時間培養することによって行われた｡His-tagged P3融合蛋白は可溶性蛋白質として発現し,Ni-NTA担体を用いて精製された.His-tagged P4融合蛋白は不溶性の封入体を形成したが,8M尿素によって可溶化され,変性条件下で同様に精製された｡