 |
PDBsum entry 2bb5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Transport protein
|
PDB id
|
|
|
|
2bb5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Structural basis for mammalian vitamin b12 transport by transcobalamin.
|
|
|
Authors
|
|
J.Wuerges,
G.Garau,
S.Geremia,
S.N.Fedosov,
T.E.Petersen,
L.Randaccio.
|
|
|
Ref.
|
|
Proc Natl Acad Sci U S A, 2006,
103,
4386-4391.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Cobalamin (Cbl, vitamin B(12)) serves for two essential cofactors in mammals.
The pathway for its intestinal absorption, plasma transport, and cellular uptake
uses cell surface receptors and three Cbl-transporting proteins, haptocorrin,
intrinsic factor, and transcobalamin (TC). We present the structure
determination of a member of the mammalian Cbl-transporter family. The crystal
structures of recombinant human and bovine holo-TCs reveal a two-domain
architecture, with an N-terminal alpha(6)-alpha(6) barrel and a smaller
C-terminal domain. One Cbl molecule in base-on conformation is buried inside the
domain interface. Structural data combined with previous binding assays indicate
a domain motion in the first step of Cbl binding. In a second step, the weakly
coordinated ligand H(2)O at the upper axial side of added H(2)O-Cbl is displaced
by a histidine residue of the alpha(6)-alpha(6) barrel. Analysis of amino acid
conservation on TC's surface in orthologous proteins suggests the location of
the TC-receptor-recognition site in an extended region on the alpha(6)-alpha(6)
barrel. The TC structure allows for the mapping of sites of amino acid variation
due to polymorphisms of the human TC gene. Structural information is used to
predict the overall fold of haptocorrin and intrinsic factor and permits a
rational approach to the design of new Cbl-based bioconjugates for diagnostic or
therapeutic drug delivery.
|
|
|
|
|
|
|
|
Figure 2.
Fig. 2. Cbl interactions with bovine TC (monoclinic crystal
form). (A) Stereoview of the F[o] - F[c] omit electron density
map at 2.0-Å resolution around the coordination of His-175
N  to the Co ion of Cbl
(contour level 3  ). Some solvent water
molecules are shown as red spheres, one of which forms a H-bond
to His-175 N  . The Co ion (magenta)
is axially coordinated by the imidazole N at a distance of 2.13
Å (above the corrin plane) and by the
dimethylbenzimidazole nitrogen N3B at 2.09 Å. (B) Scheme
of polar interactions. H-bonds are shown as dotted lines (red,
to residues in the  -domain; blue, to
residues in the  -domain; green,
solvent-mediated interactions). The main or side chain is
indicated for residues in direct contact with Cbl, whereas dots
indicate residues linked to Cbl via solvent molecules (11 H[2]O
and a Cl- ion from NaCl salt). The same scheme of direct
contacts is observed in human TC (to translate from bovine to
human TC numbering, see Fig. 3).
|
|
Figure 5.
Fig. 5. Mapping the amino acid conservation among seven TCs
(Fig. 9B) on the molecular surface of human TC. Color coding:
red, identity; orange, conserved; yellow, semiconserved; white,
not conserved. The view to the -domain is as in Fig.
1C. The conserved region proposed as TC's receptor-recognition
site is located on the right half and involves the surface of
the labeled helices 3- 6 and their loops. A
low level of conservation is present on the -domain surface.
|
|
|
|
|
|
|
|
|
|
