High worldwide conservation of a Helicobacter pylori outer membrane protein

Abstract

The genetic diversity and evolution of homD, coding for Helicobacter pylori outer membrane protein (OMP) was investigated in a panel of approximately 200 clinical and reference strains, isolated from patients from different geographical origins and presenting different gastric diseases. PCR, sequencing and bioinformatics analyses were used. The homD gene was present in all strains, at a conserved locus, and showed a low genomic diversity, displaying high similarity at both nucleotide and amino acid level. A similarity plot analysis also showed a high level of sequence conservation, although a small region (~30 nucleotides) differed between Western strains and the other strains (East Asian/Ameridian and African). This region was also found in some allelic variants of another hom family member, the homC gene, suggesting the existence of recombination events between these two OMP encoding genes. Sequence analysis of the HomD predicted protein showed a N terminus region with a variable number of KP motif repeats (2 9 KP), with a correlation between the lowest number of KP motif repeats (£4 KP) and peptic ulcer disease and the highest number of repeats (£7 KP) and gastritis. In silico analysis of the HomD protein showed that the region of KP motif repeats exhibits a strong hydrophilicity and antigenicity and a high probability of being exposed to the bacterial surface, suggesting that HomD is immunogenic. These results suggest that homD gene is an important H. pylori antigen and, because of its high global conservation, it is likely to constitute a new vaccine target