Proteins that act as antigens during the process of infection can be potential targets for the development of vaccines. In the case of O. tsutsugamushi, a number of major antigens were identified early in the molecular analysis of the organism (Oaks et al., 1989). One among these proteins was an antigen designated by size the 47-kDa antigen. Subsequent analysis of the protein indicated that it shows homology to members of the HtrA (high-temperature requirement A) protein family. HtrA proteins are characterized by serine protease and chaperone activities. Bacterial HtrAs are located in the periplasm and outer membrane of Gram-negative bacteria. The 47-kDa protein of O. tsutsugamushi has been shown to contain a trypsin domain, and it has significant sequence homology to the human HtrA1 (hHtrA1) protein.
The first reports of the DNA sequence for the 47-kDa (htrA) gene was the deposition of the sequence from the Kato strain in 1994. Subsequently, a few unpublished reports (with deposits in the DNA databases) occurred, until a major study of variation among 17 isolates was reported in 2013 (Jiang et al., 2013).
Additional sequences have become available including a number through recent releases of partial or complete genome sequences. As of August 2017, complete sequences of the 47-kDa (htrA) gene were available from 66 isolates (several additional complete sequences also exist because a number of isolates have been examined multiple times). In addition, 10 other isolates have been examined for a portion of the gene (ranging from 119 bp up to 773 bp of the ~1400 bp gene sequence).
Phylogenetic analyses of the dataset of complete 47-kDa (htrA) sequences will be included on this page in the future. In the interim, the phylogenetic analysis of the nucleotide sequences appearing in Jiang et al. (2013) is given below.
