 |
PDBsum entry 1ywm
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Surface active protein
|
PDB id
|
|
|
|
1ywm
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Crystal structure of the n-Terminal domain of the group b streptococcus alpha c protein.
|
|
|
Authors
|
|
T.C.Aupérin,
G.R.Bolduc,
M.J.Baron,
A.Heroux,
D.J.Filman,
L.C.Madoff,
J.M.Hogle.
|
|
|
Ref.
|
|
J Biol Chem, 2005,
280,
18245-18252.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Group B Streptococcus (GBS) is the leading cause of bacterial pneumonia, sepsis,
and meningitis among neonates and an important cause of morbidity among pregnant
women and immunocompromised adults. Invasive diseases due to GBS are attributed
to the ability of the pathogen to translocate across human epithelial surfaces.
The alpha C protein (ACP) has been identified as an invasin that plays a role in
internalization and translocation of GBS across epithelial cells. The soluble
N-terminal domain of ACP (NtACP) blocks the internalization of GBS. We
determined the 1.86-A resolution crystal structure of NtACP comprising residues
Ser(52) through Leu(225) of the full-length ACP. NtACP has two domains, an
N-terminal beta-sandwich and a C-terminal three-helix bundle. Structural and
topological alignments reveal that the beta-sandwich shares structural elements
with the type III fibronectin fold (FnIII), but includes structural elaborations
that make it unique. We have identified a potential integrin-binding motif
consisting of Lys-Thr-Asp(146), Arg(110), and Asp(118). A similar arrangement of
charged residues has been described in other invasins. ACP shows a heparin
binding activity that requires NtACP. We propose a possible heparin-binding
site, including one surface of the three-helix bundle, and nearby portions of
the sandwich and repeat domains. We have validated this prediction using assays
of the heparin binding and cell-adhesion properties of engineered fragments of
ACP. This is the first crystal structure of a member of the highly conserved
Gram-positive surface alpha-like protein family, and it will enable the
internalization mechanism of GBS to be dissected at the atomic level.
|
|
|
|
|
|
|
|
Figure 2.
FIG. 2. Stereo ribbon representation of the structure of
the N-terminal domain of S. agalactiae Alpha C protein.  -sheets
are shown in burgundy,  -helices in blue, and
3[10]-helices in green. Figures were drawn with RIBBONS (67) and
rendered with POV-Ray.
|
|
Figure 5.
FIG. 5. Molecular surface representation of the N-terminal
domain of alpha C protein. The views are related by a rotation
of 180° about the vertical axis. The structure exhibits a
highly acidic surface (red). However, we have identified two
positively charged clusters, BR1 and BR2 (blue), as potential
glycosaminoglycan-binding sites. Figures were drawn with GRASP
(70).
|
|
|
|
|
|
The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
18245-18252)
copyright 2005.
|
|
|
Secondary reference #1
|
|
|
Title
|
|
Large, Identical, Tandem repeating units in the c protein alpha antigen gene, Bca, Of group b streptococci.
|
|
|
Authors
|
|
J.L.Michel,
L.C.Madoff,
K.Olson,
D.E.Kling,
D.L.Kasper,
F.M.Ausubel.
|
|
|
Ref.
|
|
Proc Natl Acad Sci U S A, 1992,
89,
10060-10064.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
Secondary reference #2
|
|
|
Title
|
|
The alpha c protein mediates internalization of group b streptococcus within human cervical epithelial cells.
|
|
|
Authors
|
|
G.R.Bolduc,
M.J.Baron,
C.Gravekamp,
C.S.Lachenauer,
L.C.Madoff.
|
|
|
Ref.
|
|
Cell Microbiol, 2002,
4,
751-758.
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
Secondary reference #3
|
|
|
Title
|
|
Alpha c protein of group b streptococcus binds host cell surface glycosaminoglycan and enters cells by an actin-Dependent mechanism.
|
|
|
Authors
|
|
M.J.Baron,
G.R.Bolduc,
M.B.Goldberg,
T.C.Aupérin,
L.C.Madoff.
|
|
|
Ref.
|
|
J Biol Chem, 2004,
279,
24714-24723.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Figure 11.
FIG. 11. Alpha C protein binds heparin by dot blot.
Full-length 1-repeat alpha C protein (ACP) and 9-repeat ACP, as
well as the N-terminal region ACP protein, 9RR, Alp3, and BSA
proteins were immobilized on nitrocellulose in equal quantities
and then incubated with heparin-albumin biotin, washed,
incubated with avidin, washed, and developed. As shown, 1
µg of full-length ACP proteins bound heparin more
effectively than the same amount of either the N-terminal
protein or the 9RR protein. Full-length Alp3 protein bound
heparin also. In blots using less protein per dot, visible
signal from heparin binding remained when the amount of
full-length 9-repeat ACP was diminished to as low as 0.04 µg.
|
|
Figure 13.
FIG. 13. Schematic of 9-repeat ACP structure. ACP includes
an N-terminal domain, repeat region(s) of 82 amino acids each,
and C-terminal domain. Numbers to the right of the diagram refer
to amino acid number; the first 56 amino acids encode a signal
sequence that is cleaved prior to surface expression. Structural
analysis indicates that residues in the distal portion of the
N-terminal region (Asp160-Leu226) form a pocket that is
compatible with heparin-binding activity.2 Residues in the
adjacent portion of the repeat region may also contribute
features compatible with heparin-binding activity.
|
|
|
|
|
|
The above figures are
reproduced from the cited reference
with permission from the ASBMB
|
|
Author's comment:
Functional studies indicate host GAG structures, and in particular heparan sulfate proteoglycans (HSPGs), serve as receptors for ACP. Data supporting this hypothesis include: (1) inhibition of this interaction by pretreatment of cells with sodium chlorate, which prevents sulfation of eukaryotic cell structures; (2) inhibition of this interaction by pretreatment of cells with heparitinases but not chondroitinase ABC; (3) inhibition of this interaction in the presence of soluble heparin or heparan sulfate (but less so by chondroitin or other GAG molecules tested); (4) binding of ACP to heparin-albumin-biotin in vitro; and (5) inhibition of this interaction by GAG derived from host cells.
Epitope mapping indicates that both the N-terminal region and at least one "repeat" are required for optimal binding to host cell GAG. Compatible with these data, crystallographic data from the N-terminal region reveal a putative heparin-binding domain, BR2, near the junction with the repeat-region that may extend into the repeat-region as well.
Miriam Baron
|
|
|
|
|
|
|
