Effects of amino acid replacements around the reactive site of chicken ovomucoid domain 3 on the inhibitory activity toward chymotrypsin and trypsin

We have previously shown that replacing the P1-site residue(Ala) of chicken ovomucoid domain 3 (OMCHI3) with a Met or Lysresults in the acquisition of inhibitory activity toward chymotrypsinor trypsin, respectively. However, the inhibitory activitiesthus induced are not strong. In the present study, we introducedadditional amino acid replacements around the reactive siteto try to make the P1-site mutants more effective inhibitorsof chymotrypsin or trypsin. The amino acid replacement AspTyrat the P2' site of OMCHI3(P1Met) resulted in conversion to a35000-fold more effective inhibitor of chymotrypsin with aninhibitor constant (K_i) of 1.17x10^–11 M. The K_i valueof OMCHI3(P1Met, P2'Ala) indicated that the effect on the interactionwith chymotrypsin of removing a negative charge from the P2'site was greater than that of introducing an aromatic ring.Similarly, enhanced inhibition of trypsin was observed whenthe AspTyr replacement was introduced into the P2' site of OMCHI3(P1Lys).Two additional replacements, AspAla at the P4 site and ArgAlaat the P3' site, made the mutant a more effective inhibitorof trypsin with a K_i value of 1.44x10^–9 M. By contrast,ArgAla replacement at the P3' site of OMCHI3(P1Met, P2'Tyr)resulted in a greatly reduced inhibition of chymotrypsin, andAspAla replacement at the P4 site produced only a small changewhen compared with a natural variant of OMCHI3. These resultsclearly indicate that not only the P1-site residue but alsothe characteristics, particularly the electrostatic properties,of the amino acid residues around the reactive site of the proteaseinhibitor determine the strength of its interactions with proteases.Furthermore, amino acids with different characteristics arerequired around the reactive site for strong inhibition of chymotrypsinand trypsin.     

三步沉淀法纯化鸡卵类黏蛋白

鸡卵类黏蛋白（hen’s egg ovomucoid,HOVM）是鸡蛋清中最重要的过敏原蛋白,探讨三步沉淀（一步三氯乙酸沉淀以及两步硫酸铵盐析沉淀）从鸡蛋清中提取并纯化HOVM的工艺条件,并利用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳以及高效液相色谱（high performance liquid chromatography,HPLC）技术检测纯化效果。结果表明：用等体积去离子水稀释的鸡卵清液加入质量分数10%三氯乙酸去除大部分杂蛋白后,所得上清液加入硫酸铵至终饱和度50%,盐析沉淀进一步去除非HOVM的杂蛋白,上清液中最后再追加硫酸铵至终饱和度80%,离心所得沉淀再经过透析冻干即为高纯度的HOVM;HPLC（检测波长220 nm）检测所获HOVM的纯度为99.202%,此工艺条件下得到HOVM的提取率约为27.05%。     

鸡卵类黏蛋白过敏原性的在体与离体实验

通过观察卵类黏蛋白引起的豚鼠过敏性休克以及对致敏豚鼠离体肠平滑肌过敏性收缩反应（Schultz- Dale反应）的影响,研究鸡卵类黏蛋白的过敏原性,并初步建立其过敏实验的动物模型。结果显示：1）在实验 观察剂量下,1 mg/mL卵清白蛋白组豚鼠100%出现过敏性休克并死亡,全身性过敏反应呈极强阳性（4 分）; 卵类黏蛋白组豚鼠的反应与卵白蛋白组相似（P＞0.05）,大部分动物出现死亡,全身性过敏反应100%呈阳性 （2.04～3.68 分）;不同剂量的卵类黏蛋白引起的豚鼠全身过敏反应呈现出剂量依赖性,当致敏剂量为4 mg/mL 时,全身性过敏反应评分为3.68。2）卵类黏蛋白对Schultz-Dale反应的影响也与卵清白蛋白相似,使致敏的肠平滑 肌收缩活动明显加强;以2 mg/mL致敏时,豚鼠离体肠收缩力改变率最高,为538.5%。3）不同致敏剂量卵类黏蛋 白组豚鼠血清免疫球蛋白（immunoglobulin,Ig）G水平较对照组明显升高,且呈剂量依赖性。由此建立的卵类黏 蛋白在体与离体过敏实验的动物模型可用以检测卵类黏蛋白过敏原及评价其过敏原的消减效果。     

鸡卵类黏蛋白结构与性质研究进展

鸡卵类黏蛋白是鸡蛋中最主要也是过敏原性最强的过敏原蛋白。本文总结该蛋白的结构,包括氨基酸序列、糖基组成、二硫键位置、二级结构以及组成该蛋白的3 个结构域,并描述其理化性质,最后着重分析讨论其过敏原性,特别是其分子结构中二硫键、糖基和结构域等因素与过敏原性之间的内在联系。     

色谱法在鸡蛋清主要过敏原分离纯化中研究进展

鸡蛋营养丰富,同时也是引起人体过敏的主要食物之一。蛋清中含有4种主要过敏原,包括卵白蛋白、卵转铁蛋白、卵类黏蛋白和溶菌酶。概述了鸡蛋中4种主要过敏原的理化特性及色谱法纯化过敏原的研究进展,旨在为规模化分离得到高纯度和高活性的过敏原提供参考。     

The allergenicity of ovomucoid and the effect of its elimination from hen's egg white

In order to remove the ovomucoid from hen's egg white, chitin and hydrazide polystyrene beads were used as affinity ligands with 8.9 and 7.1 mg trypsin g^?1 ligand respectively. Ovomucoid was successfully depleted using the trypsin affinity column without hydrolysation of the other egg white constituents. The components of the egg white were purified by high‐performance liquid chromatography, and then the allergenicity of each of these components was compared with that of pooled human serum derived from patients who are allergic to hen's eggs. The importance of using pure protein for studies of the allergenicity of egg white is highlighted, and it was determined (using an enzyme‐immunosorbent assay) that ovomucoid and ovalbumin are major allergenic proteins in egg white. The ovomucoid‐eliminated egg white preparation exhibited significantly less IgE‐binding activity than normal egg white. The ovomucoid‐specific IgE antibodies may have important implications with regard to the egg‐allergic reaction in humans. © 2001 Society of Chemical Industry