Download Orientia tsutsugamushi is a parasitic bacterium living inside human

Ankyrin repeat and tetratricopeptide repeat genes — potential disease
genes for scrub typhus, a severe human disease caused by Orientia
tsutsugamushi
Jun Yin
Orientia tsutsugamushi is a parasitic bacterium living inside human cells. It can cause a
severe human disease, scrub typhus. In order to understand why it causes disease, Orientia’s
genome DNA, the whole DNA of this bacterium, was sequenced. Interestingly, a large
number of so-called repeat genes were found in Orientia’s genome. Such genes encode
proteins where series 20-40 amino acids are repeated szeveral times. The most common
repeat genes in Orientia were the ankyrin repeat (ANK) genes and the tetratricopeptide repeat
(TPR) genes. ANK and TPR genes encode proteins that help two proteins interact with each
other. Considering their high number in Orientia and their role in mediating protein
interaction, it is possible that ANK and TPR proteins contribute to scrub typhus.
In this project, DNA sequences from Orientia and its two relatives Wolbachia and
Rickettsia were searched to identify ANK and TPR genes. Several new ANK and TPR genes
were found that had not been described before. ANK and TPR genes in Orientia were divided
into different families and groups by sequence similarity and flanking genes. There was one
long “master gene” in each TPR gene group, which could be derived. This master gene could
be the ancestor of the other genes in the group. Most TPR genes were neighbors of tra genes.
tra genes encode proteins that are components of a bacteria secretion system that can
participate in secretion of harmful bacterial proteins into human cells. Thus TPR genes may
be associated with this secretion system and thereby contribute to scrub typhus.
Different TPR gene sequences from Rickettsia, Wolbachia and Orientia were compared in
order to understand the evolution of these genes. The TPR gene sequences from Orientia were
more similar to the ones from Rickettsia than the ones from Wolbachia. The result was similar
when using another gene sequences (rpoA) from these bacteria. This suggests that Orientia is
a member of the Wolbachia and Rickettsia group.
This study of ANK and TPR genes may provide clues to the distribution of repeat genes
among bacteria, give insights to their relationship with Orientia’s pathogenicity, and help to
realize their role in Orientia’s evolution.
Degree project in biology
Examensarbete i biology, 20p, Uppsala Universitet, våren 2006
Biology Education Centre and Department of Molecular Evolution, Uppsala University
Supervisor: Siv Andersson