Binding of the Bovine and Porcine Pancreatic Secretory Trypsin Inhibitor (Kazal) To Human Leukocyte Elastase: A Thermodynamic Study

Abstract

The effect of pH and temperature on the apparent association equilibrium constant (K_a) for the binding of the bovine and porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, PSTI) to human leukocyte elastase has been investigated. At pH8.0, values of the apparent thermodynamic parameters for human leukocyte elastase: Kazal-type inhibitor complex formation are: bovine PSTT – K_a = 6.3 × 10⁴M^?1, δ5G° = -26.9kJ/mol, δH° = +11.7kJ/mol, and δS° = +1.3 × 10² entropy units; porcine PSTI –K_a = 7.0 × 10³M^?1,δG° = -21.5kJ/mol, δH° = +13.0kJ/mol, and δS° = +1.2 × 10² entropy units (values of K_a δG° and δS° were obtained at 21.0°C; values of δH° were temperature independent over the range (between 5.0°C and 45.0°C) explored). On increasing the pH from 4.5 to 9.5, values of K_a for bovine and porcine PSTI binding to human leukocyte elastase increase thus reflecting the acidic pK-shift of the His57 catalytic residue from ?7.0, in the free enzyme, to ?5.1, in the serine proteinase: inhibitor complexes. Thermodynamics of bovine and porcine PSTI binding to human leukocyte elastase has been analyzed in parallel with that of related serine (pro)enzyme/Kazal-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of bovine and porcine PSTI to human leukocyte elastase was related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).     

Binding of the Recombinant Proteinase Inhibitor Eglin c,of the Soybean Bowman-Birk Proteinase Inhibitor and of its Chymotrypsin and Trypsin Inhibiting Fragments to Leu-Proteinase,the Leucine Specific Serine Proteinase from Spinach (Spinacia oleracea L.) Leaves: Thermodynamic Study

Abstract

The effect of pH and temperature on the apparent association equilibrium constant (K_a) for the binding of the recombinant proteinase inhibitor eglin c (eglin c), of the soybean Bowman-Birk proteinase inhibitor (BBI) and of its chymotrypsin and trypsin inhibiting fragments (F-C and F-T, respetively) to Leuproteinase, the leucine specific serine proteinase from spinach (Spinacia oleracea L.) leaves, has been investigated. On lowering the pH from 9.5 to 4.5, values of K_a (at 21°C) for complex formation decrease thus reflecting the acidic pK-shift of the hystidyl catalytic residue from ～6.9, in the free Leu-proteinase, to ～5.1, in the enzyme: inhibitor adducts. At pH 8.0, values of the apparent thermodynamic parameters for the proteinase:inhibitor complex formation are: Leu-proteinase:eglin c - K_a = 2.2 × 10¹¹ M^-1, δG°= - 64kJ/mol, δH° = + 5.9kJ/mol, and δS° = + 240J/molK; Leu-proteinase:BBI - K_a = 3.2 × 10¹⁰ M^-1, δG° = - 59kJ/mol, δH°= + 8.8kJ/mol, and δS° = + 230J/molK; and Leu-proteinase:F-C - K_a = 1.1 × 10⁶ M^-1, δG°= - 34kJ/mol, δH° = + 18J/mol, and δS° = + 180J/molK (values of K_a, δG° and δS° were obtained at 21.0°C; values of δH° were temperature-independent over the range explored, i.e. between 10.0°C and 40.0°C). F-T does not inhibit Leu-proteinase up to an inhibitor concentration of 1.0 × 10^-3 M, suggesting that the upper limit of K_a is 1 × 10² M^-1. Considering the known molecular models, the observed binding behaviour of eglin c, BBI, F-C and F-T to Leu-proteinase has been related to the inferred stereochemistry of the enzyme/inhibitor contact region     

大豆Kunitz型胰蛋白酶抑制剂新类型Tid的全序列分析

大豆ｋｕｎｉｔｚ型胰蛋白酶抑制剂（ＳＢＴｉＡ２）是一种大量存在于大豆（Ｇｌｙｃｉｎｅｍａｘ）中的种子贮藏蛋白．虽然对它的生化特性及结构已有较多的研究,但它在体内的主要功能仍不很清楚．国际上所发现的３个由显性等位基因Ｔｉａ、Ｔｉｂ、Ｔｉｃ编码的大豆ｋｕｎｉｔｚ胰蛋白酶抑制剂的氨基酸顺序已被明确测定,相互间有一到多个氨基酸残基的不同［１］．Ｔｉｄ是从我国１５０００余份大豆资源中筛选到的唯一一份ｋｕｎｉｔｚ型胰蛋白酶抑制剂位点的新类型,遗传分析证明它是另一个ＳＢＴｉＡ２的显性等位基因［２,３］．严…     

人二氢乳清酸脱氢酶蛋白的表达、纯化及其与新型抑制剂的晶体结构

人二氢乳清酸脱氢酶（human dihydroorotate dehydrogenase, hDHODH）是催化嘧啶从头合成途径的一个关键酶。近年来,多种研究表明,抑制该酶可缓解类风湿性关节炎的症状。但该酶的抑制剂甚少,寻找该酶的高效抑制剂具有重要意义。本研究利用PCR技术扩增hDHODH基因,构建重组质粒pET-19b-hDHODH,并在大肠杆菌(Escherichia coli, E.coli ) BL21(DE3)中表达,获得可溶性蛋白质。用Ni2+-NTA亲和层析柱对蛋白质进行纯化,获得较高（90%）纯度的hDHODH蛋白,将蛋白质与抑制剂3-(5-乙硫基)-1H-1, 2, 4-三氮唑-3-)苯甲酸和底物DHO混合孵育。用Hampton试剂盒初筛晶体并用棋盘法进行优化,获得晶形完美、衍射能力很强的hDHODH蛋白复合物单晶。用X射线衍射晶体,用CCP4、Coot软件解析结构,获得hDHODH蛋白复合物晶体结构。从解析的结构中可以看出,抑制剂与蛋白质的吻合度非常高,且抑制剂通过亲水的羧基端与蛋白质356位和147位的酪氨酸形成氢键网络。抑制剂的5元环与蛋白质359位的亮氨酸和360位的苏氨酸相互作用,使抑制剂与蛋白质牢固结合。该复合物晶体结构的顺利解析,将为开发新型特异性抗类风湿性关节炎药物提供重要基础。     

核糖核酸酶抑制蛋白变体RIv在大肠杆菌和家蚕细胞中的表达

人源的核糖核酸酶抑制蛋白 (ribonucleaseinhibitor,RI)是一种富含亮氨酸和半胱氨酸残基的酸性蛋白质 ,分子量为 5 0kD。从人胚胎肝cDNA文库中克隆到一个核糖核酸酶抑制蛋白RI基因的变体 (ribonucleaseinhibitorvari ant,RIv)。序列分析表明 ,与RI相比较 ,RIv序列中仅有Arg359Ala和Leu36 5Pro两个氨基酸突变 ,而核苷酸同源性较低 ,为 78%。将RIv克隆于pET2 8a( ) ,并转化大肠杆菌BL2 1(DE3) ,IPTG诱导表达 ,利用 6×His亲和层析柱纯化得到了His RIv重组蛋白。将RIv克隆于转移载体pBacPAK8,利用家蚕核型多角体病毒 (BmNPV)表达系统表达得到重组RIv。体外活性测定实验表明 ,重组RIv具有抑制牛胰RNaseA酶解 2 8S和 18SrRNA的作用。     

人组织型基质金属蛋白酶抑制剂-1在Pichia pastoris酵母中重组表达研究

 为研究组织型基质金属蛋白酶抑制剂 (TIMPs)的分子作用机制 ,探讨了在 Pichia pastoris酵母中高效表达分泌型人组织型基质金属蛋白酶抑制剂 - 1 (TIMP- 1 )的技术路线 ,并对产物性质进行初步研究 .通过 PCR从含有 TIMP- 1基因的 p BS质粒获得了该基因的全长序列 ,构建了 p PIC9/T1表达载体 ,电击法转化酵母 ,通过表型筛选和 PCR鉴定证实了目的基因已稳定整合入 Pichiapastoris酵母基因组中 .SDS- PAGE表明表达量高达 40 mg/L培养上清 .用免疫印迹法确定了产物的正确性 ;同时 ,反向明胶酶谱法证明了重组蛋白具有抑制基质金属蛋白酶的活性 .