IrgA is an iron-regulated virulence factor for infection in an animal model with classical Vibrio cholerae strain 0395. We detected gene sequences hybridizing to irgA at high stringency in clinical ...isolates in addition to 0395, including another classical strain of V. cholerae, three V. cholerae strains of the El Tor biotype, three non-O1 isolates of V. cholerae, and individual isolates of Vibrio parahaemolyticus, Vibrio fluvialis, and Vibrio alginolyticus. No hybridization to irgA was seen with chromosomal DNA from Vibrio vulnificus or Aeromonas hydrophila. To verify that irgA is the structural gene for the major iron-regulated outer membrane protein of V. cholerae, we determined the amino-terminal sequence of this protein recovered after gel electrophoresis and demonstrated that it corresponds to the amino acid sequence of IrgA deduced from the nucleotide sequence. Gel electrophoresis showed that two El Tor strains of V. cholerae had a major iron-regulated outer membrane protein identical in size and appearance to IrgA in strain 0395, consistent with the findings of DNA hybridization. We have previously suggested that IrgA might be the outer membrane receptor for the V. cholerae siderophore, vibriobactin. Biological data presented here, however, show that a mutation in irgA had no effect on the transport of vibriobactin and produced no defect in the utilization of iron from ferrichrome, ferric citrate, haemin or haemoglobin. The complete deduced amino acid sequence of IrgA demonstrated homology to the entire class of Escherichia coli TonB-dependent proteins, particularly Cir. Unlike the situation with Cir, however, we were unable to demonstrate a role for IrgA as a receptor for catechol-substituted cephalosporins. The role of IrgA in the pathogenesis of V. cholerae infection, its function as an outer membrane receptor, and its potential interaction with a TonB-like protein in V. cholerae remain to be determined.
The Pseudo-Symmetric Structure of Pb(SPh)2 Rae, A. D.; Craig, D. C.; Dance, I. G. ...
Acta crystallographica. Section B, Structural science,
June 1997, Letnik:
53, Številka:
3
Journal Article
Recenzirano
The crystal structure of Pb(SC
6
H
5
)2 is pseudo-
C
-centred orthorhombic,
a
= 54.06 (1),
b
= 11.468 (1),
c
= 7.4387 (8) Å, \alpha = \beta = \gamma = 90°,
Z
= 16, and may be described as a partial ...ordering of a 1:1 disordered parent structure of symmetry
Pmcn
,
Z
= 4 (
a
′ =
a
/2,
b
′ =
b
/2,
c
′ =
c
), in which the mirror imposes a 1:1 disorder on two-dimensionally polymeric layers perpendicular to
a
*. An ideally ordered structure has monoclinic space group
C
112
1
/
d
(
P
2
1
/
c
using an alternative axis system
b
,
c
,
a
+
b
/2), but may also be described as two inversion-related substructures of
Cmc
2
1
pseudo- symmetry, where the
b
-glide planes of one substructure coincide with the mirror planes of the other and
vice versa
. Moving one substructure by
b
/2 relative to the other creates a different orientation of the structure. The crystal studied showed a partial disorder of each substructure relative to origins
b
/2 apart 0.964 (4):0.036 for one substructure and 0.584 (3):0.416 for the other. This lowers the symmetry of the average structure to
C
112
1
with intensities realistically described as
K
2
(1−\delta)|
F
(
hkl
)|
2
+ \delta|
F
(
hkl
)|
2
, where
K
2
for
h
odd,
k
odd reflections is 0.444 (7) of the value for
h
even,
k
even reflections, \delta is 0.325 (5) and
F
(
hkl
) is the structure factor for an ideally ordered structure. Final values for
R
of 0.046 and 0.090 were obtained for the 844
h
even,
k
even and 687
h
odd,
k
odd reflections with
I
(
h
) > 3\sigma(
I
(
h
)) used in refinement. A bond-valence interpretation of the bonding within the polymeric layer structure is given.
