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PDBsum entry 2fqw
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Transport protein
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PDB id
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2fqw
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References listed in PDB file
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Key reference
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Title
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The pnra (tp0319; tmpc) lipoprotein represents a new family of bacterial purine nucleoside receptor encoded within an ATP-Binding cassette (abc)-Like operon in treponema pallidum.
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Authors
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R.K.Deka,
C.A.Brautigam,
X.F.Yang,
J.S.Blevins,
M.Machius,
D.R.Tomchick,
M.V.Norgard.
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Ref.
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J Biol Chem, 2006,
281,
8072-8081.
[DOI no: ]
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PubMed id
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Abstract
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Treponema pallidum, the bacterial agent of syphilis, cannot be cultivated in
vitro. This constraint has severely impeded the study of the membrane biology of
this complex human pathogen. A structure-to-function approach thus was adopted
as a means of discerning the likely function of Tp0319, a 35-kDa cytoplasmic
membrane-associated lipoprotein of T. pallidum formerly designated as TmpC. A
1.7-A crystal structure showed that recombinant Tp0319 (rTp0319) consists of two
alpha/beta domains, linked by three crossovers, with a deep cleft between them
akin to ATP-binding cassette (ABC) receptors. In the cleft, a molecule of
inosine was bound. Isothermal titration calorimetry demonstrated that rTp0319
specifically binds purine nucleosides (dissociation constant (Kd) approximately
10(-7) M). This predilection for purine nucleosides by rTp0319 is consistent
with its likely role as a receptor component of a cytoplasmic
membrane-associated transporter system. Reverse transcription-PCR analysis of
RNA isolated from rabbit tissue-extracted T. pallidum additionally showed that
tp0319 is transcriptionally linked to four other downstream open reading frames,
thereby supporting the existence of an ABC-like operon (tp0319-0323). We herein
thus re-name tp0319 as purine nucleoside receptor A (pnrA), with its operonic
partners tp0320-0323 designated as pnrB-E, respectively. Our study not only
infers that PnrA transports purine nucleosides essential for the survival of T.
pallidum within its obligate human host, but to our knowledge, this is the first
description of an ABC-type nucleoside transport system in any bacterium. PnrA
has been grouped with a functionally uncharacterized protein family (HBG016869),
thereby implying that other members of the family may have similar
nucleoside-binding function(s).
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Figure 2.
Structures and numbering conventions for nucleosides used in
this study.
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Figure 6.
Stereo diagram of the superposition of rTp0319 and RBP.
Smoothed traces through the C[α] positions of the superposed
rTp0319 (blue) and RBP (orange) are shown. The orientation is
similar to that shown in Fig. 1.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2006,
281,
8072-8081)
copyright 2006.
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