Abstract:

Objective To clone the Helicobacter pylori （Hp） hp0169 gene and conduct the crystallographic study， and to clarify its secondary and tertiary structures. Methods The hp0169 gene and its encoded protein sequence of the Hp NCTC26695 strain were retrieved from the UniProt database. Bioinformatics method was used to analyze the physicochemical properties of the Hp recombinant protease （HpPrtC） protein； SOPMA and DNAStrar softwares were used to predict the secondary structure characteristics of HpPrtC protein； SWISS-MODEL software was used to construct the tertiary structure of the HpPrtC protein； IEDB and ABCpred softwares were used to predict the antigenic epitopes of the B lymphocytes HpPrtC protein； SYFPEITMI website was used to predict the antigenic epitopes of the T lymphocytes of HpPrtC protein； the expert pool （EP） and random forest （RF） algorithms were used to predict the crystallizability of the HpPrtC protein；the HpPrtC recombinant protein was expressed in the prokaryotic system； the HpPrtC recombinant protein was purified by Ni²⁺ affinity chromatography and size-exclusion chromatography；the crystallization conditions for HpPrtC were screened by crystallization kit. Results The hp0169 gene contained 1 269 base pairs and encoded the protein of 422 amino acids， the theoretical isoelectric point was 7.64 and the relative molecular weight was 47 300. HpPrtC was a hydrophilic and soluble protein. The number of amino acids of alpha helices of HpPrtC accounted for 35.78%， beta sheets 18.72%， beta turns 6.87%， and random coils 38.63%. The antigen epitope analysis results showed that HpPrtC contained five dominant linear epitopes of B lymphocytes， three conformational epitopes， and multiple potential dominant epitopes of T lymphocytes. The homology modeling results showed that HpPrtC formed a dimer， and each monomer displayed a barrel structure surrounded by β sheets， alpha helices， and random coils. HpPrtC was predicted to have moderate crystallizability without signal peptides and transmembrane helices. Small clustered needle-like crystals of HpPrtC were obtained under the conditions of 0.2 mol·L^-1 magnesium chloride， 0.1 mol·L^-1 tris （hydroxymethyl） amino methane（Tris）， 3.4 mol·L^-1 hexanediol， and pH=8.5. Conclusion HpPrtC is a hydrophilic protein that forms a dimeric structure and crystallizes into small clustered needle-like crystals under suitable conditions. HpPrtC contains dominant antigenic epitopes of the T lymphocytes and B lymphocytes and can serve as an antigen for the design of Hp vaccines to establish the multivalent fusion vaccines or multi-epitope vaccines； the results provide an experimental basis for the prevention and control of Hp.

Key words: Helicobacter pylori, hp0169 gene, Crystallization, Antigenic epitope, Bioinformatics