广谱抗革兰氏阴性菌单克隆抗体3A8识别表位的初步研究

Characterization of the epitopes recognized by monoclonal antibody 3A8 specific to broad-spectrum Gram-negative bacteria

目的:利用噬菌体肽库技术筛选抗广谱革兰氏阴性菌与LPS单克隆抗体3A8的识别表位,以获得来源于不同LPS的保守表位。方法:用广谱抗G-菌、LPS的单克隆抗体3A8为靶,筛选噬菌体环七肽库,ELISA鉴定阳性噬菌体克隆并测序。根据阳性保守序列合成短肽A2及A5,并与KLH载体交联,ELISA鉴定A2-KLH、A5-KLH与3A8单抗的结合。结果:随机挑选的33个噬菌体克隆中有15个可特异性与3A8结合,该结合可被LPS2630所抑制。根据阳性克隆DNA序列推导氨基酸序列,共有7种序列,均以疏水氨基酸为主,且包含保守序列Ser Pro Pro/Pro X Pro;选择所获阳性序列经设计与改造合成延长的两个环肽;经ELISA鉴定表明这些环肽可特异地与3A8结合。结论:得到可被3A8单抗特异性识别并含保守残基Ser Pro Pro/ProX Pro的阳性序列,据此合成的短肽可特异性结合3A8,提示该短肽可能模拟LPS共同表位的抗原性,有望成为疫苗候选表位。

Objective：To screen and characterize the common epitopes recognized by monoclonal antibody 3A8,which binds several kinds of Gram negative bacteria,which were recognized by monoclonol antibody 3A8 agaisnt different strains of LPS.Methods：Phage clones binding to 3A8 were screened from C7C phage displayed peptide library,the attached phage clones were eluted by LPS2630（O111：B4）.After 3 rounds of panning,the positive phage clones were identified by ELISA,and the amino acid sequences of these positive clones were deduced from DNA sequences.In order to predict how these peptide mimics interaction with 3A8,peptides（A2 and A5） based on conserved sequences of positive clones were synthesized and conjugated with KLH for further study.The binding of A2-KLH and A5-KLH to 3A8 were identified by ELISA.Results：15 of 33 phage clones were identified as positive clones and shown specific binding with 3A8.LPS2630 potently inhibited the binding of phage clone to 3A8.In analysis of the amino acid sequence,there were seven kinds of sequences containing highly hydrophilic residues,and Ser Pro Pro/Pro X Pro was the conserved sequence.The peptides A2 and A5 could bind to 3A8 specially.Conclusion：The conserved sequences containing Ser Pro Pro/Pro X Pro are obtained,which are recognized by mAb 3A8 against broad spectrum Gram negative bacteria and several strain LPS.The synthetic peptides based on the conserved sequence can bind to 3A8,indicating that the peptides can mimic a common epitope of Gram negative bacteria,which be expected as candidate epitope for vaccinization.