Affiliation:
1. Pflanzenphysiologie, Universität Osnabrück, D-49069 Osnabrück, Germany,1 and
2. Laboratory of Molecular Biology, Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, Alabama 366882
Abstract
ABSTRACT
The genome of
Chlamydia trachomatis
, one of the most prominent human pathogens, contains two structural genes coding for proteins, herein called Npt1
Ct
and Npt2
Ct
(nucleoside phosphate transporters 1 and 2 of
C. trachomatis
), exhibiting 68 and 61% similarity, respectively, to the ATP/ADP transporter from the intracellular bacterium
Rickettsia prowazekii
at the deduced amino acid level. Hydropathy analysis and sequence alignments suggested that both proteins have 12 transmembrane domains. The putative transporters were expressed as histidine-tagged proteins in
Escherichia coli
to study their biochemical properties. His
10
-Npt1
Ct
catalyzed ATP and ADP transport in an exchange mode. The apparent K
m
values were 48 (ATP) and 39 (ADP) μM. ATP and ADP transport was specific since AMP, GTP, CTP, UTP, dATP, dCTP, dGTP, and dTTP did not inhibit uptake. In contrast, His
10
-Npt2
Ct
transported all four ribonucleoside triphosphates with apparent K
m
values of 31 μM (GTP), 302 μM (UTP), 528 μM (CTP), and 1,158 μM (ATP). Ribonucleoside di- and monophosphates and deoxyribonucleotides were not substrates. The protonophore m -chlorocarbonylcyanide phenylhydrazone abolished uptake of all nucleoside triphosphates by Npt2
Ct
. This observation indicated that His
10
-Npt2
Ct
acts as a nucleosidetriphosphate/H
+
symporter energized by the proton motive force across the
Escherichia coli
cytoplasmic membrane. We conclude that Npt1
Ct
provides chlamydiae with energy whereas Npt2
Ct
catalyzes the net uptake of ribonucleoside triphosphates required for anabolic reactions.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
133 articles.
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