Identification of predominant T-and B-combined antigenic epitopes in outer membrane protein GroEL of Helicobacter pylori
Objective To screen and identify the predominant T-and B-cell (T-B) combined antigenic epitopes in outer membrane protein GroEL of Helicobacter pylori (H.pylori).Methods The entire groEL gene of H.pylori strain NCTC11637 was amplified by PCR,and then a prokaryotic expression system for groEL gene was constructed.The expressed target recombinant protein rGroEL was analyzed by SDSPAGE and purified by Ni-NTA affinity chromatography.Laser confocal microscopy was applied to determine the distribution of GroEL in H.pyloristrains of NCTC11637 and SS1.The outer membrane protein (OMP) samples were extracted from the two strains using Triton X-114 method.GroEL in OMP samples was detected by Western blot assay.Special bioinformatic softwares were used to predict T-B combined antigenic epitopes on GroEL molecule,and phage display systems for every T-B combined antigenic epitope were established.Western blot assay and ELISA were used to detect the immunoreactivity of recombinant T-B combined antigenic epitope-containing phage PⅢ proteins and artificially synthesized T-B combined antigenic epitope peptides,respectively.Results The groEL genes from H.pylori strains of NCTC11637 and SS1 showed 97.68％ ～99.63％ identities in their nucleotide and amino acid sequences.The established prokaryotic expression system could efficiently express soluble rGroEL.GroEL located on the outer membrane of H.pylori strains of NCTC11637 and SS1.Among the six major predicted T-B combined epitopes (GroEL168,GroEL258,GroEL288,GroEL365,GroEL396 and GroEL438),GroEL168 showed the strongest positive immunoblotting signal.The results of ELISA showed that the immunoreactivity of GroEL168 was also the strongest (P＜0.01),followed by GroEL258 and GroEL288 (P＜0.05).Conclusion GroEL is an outer membrane protein of H.pylori.GroEL168 being the predominant T-B combined antigenic epitope of GroEL can be used to develop multiple antigenic peptide vaccines of H.pylori. 
 
Key words: 
Helicobacter pylori;  Outer membrane protein;  GroEL;  T-B combined antigenic epitope;  Phage display