Up to 50 % of the world's population is infected with Helicobacter pylori. Colonization of
the mucus layer of the human stomach by H. pylori, is lifelong unless treated with antibiotics
(26). H. pylori, which is a neutralophilic bacterium, survives in the mucus layer of the human
stomach with the help of the enzyme urease. Urease is an enzyme that converts urea into
ammonium and carbon dioxide, thereby keeping the intracellular and periplasmic pH at
neutral. It is estimated that up to 10% of the whole cell protein consists of this nickelcofactored
enzyme (19). The nickel necessary to activate the urease is thought to come from
foodsources, such as nuts, tea and cereals, which are rich in nickel (1).
Metal ions like nickel or iron can be dangerous for bacteria, as they can react with oxygen
in order to create reactive oxygen species that in turn can destroy macromolecules like
nucleic acids, proteins and cell wall components (27). Therefore, the bacterial metal
metabolism has to be tightly regulated. In H. pylori, regulatory proteins are scarce. Only two
metal-regulatory proteins are known, the ferric uptake regulator Fur (4), and the nickel
responsive regulator NikR (31). Fur is a regulatory protein that can sense and bind
intracellular ferrous ions, and subsequently displays iron-dependent binding to conserved
promoter sequences (Fur boxes) of its target genes (17). The classical regulation is repression
of iron uptake genes in iron-replete conditions (15, 17, 33). Unlike all other Fur homologs
known so far, H. pylori Fur can also bind to Fur-boxes in an iron free form (apo-Fur), as was
shown for pfr (16) and sodB (Chapter 3).
The second metal-dependent regulatory protein is NikR, the nickel responsive regulator,
which belongs to the family of Ribbon-Helix-Helix regulatory proteins (9). NikR is directly
involved in the regulation of acid resistance via urease and nickel-uptake (Chapter 4), and
was previously demonstrated to mediate regulation of the ferric uptake regulator Fur (7, 12,
29).
The aim of this thesis was to gain further insight into the transcriptional regulation the
ferric uptake regulator Fur and the nickel responsive regulator NikR
