P. Bauerfeind et al., ALLELIC EXCHANGE MUTAGENESIS OF NIXA IN HELICOBACTER-PYLORI RESULTS IN REDUCED NICKEL TRANSPORT AND UREASE ACTIVITY, Infection and immunity, 64(7), 1996, pp. 2877-2880
Helicobacter pylori, an etiologic agent of gastritis and peptic ulcera
tion in humans, synthesizes urease, a nickel metalloenzyme, as its mos
t abundant protein. NixA, a high-affinity nickel transport protein, al
lows synthesis of catalytically active urease when coexpressed with H.
pylori urease in an Escherichia coli host. To determine whether NixA
is essential for the production of active urease in H. pylori, nixA wa
s insertionally inactivated with a kanamycin resistance cassette (aphA
) and this construct was electroporated into H. pylori ATCC 43504; all
elic exchange mutants were selected on kanamycin-containing medium. Th
e nixA mutation, confirmed by PCR, reduced urease activity by 42% (140
+/- 70 mu mol of NH3/min/mg of protein in the mutant versus 240 +/- 1
00 mu mol of NH3/min/mg of protein in the parent (P = 0.037). Rates of
nickel transport were dramatically reduced (P = 0.0002) in the nixA m
utant (9.3 +/- 3.7 pmol of Ni2+/min/10(8) bacteria) of H. pylori as co
mpared with the parent strain (30.2 +/- 8.1 pmol of Ni2+/min/10(8) bac
teria). We conclude that NixA is an important mediator of nickel trans
port in H. pylori. That residual nickel transport and urease activity
remain in the nixA mutant, however, provides evidence for the presence
of a redundant transport system in this species.