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PDBsum entry 1c3d
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References listed in PDB file
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Key reference
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Title
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X-Ray crystal structure of c3d: a c3 fragment and ligand for complement receptor 2.
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Authors
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B.Nagar,
R.G.Jones,
R.J.Diefenbach,
D.E.Isenman,
J.M.Rini.
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Ref.
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Science, 1998,
280,
1277-1281.
[DOI no: ]
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PubMed id
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Abstract
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Activation and covalent attachment of complement component C3 to pathogens is
the key step in complement-mediated host defense. Additionally, the
antigen-bound C3d fragment interacts with complement receptor 2 (CR2; also known
as CD21) on B cells and thereby contributes to the initiation of an acquired
humoral response. The x-ray crystal structure of human C3d solved at 2.0
angstroms resolution reveals an alpha-alpha barrel with the residues responsible
for thioester formation and covalent attachment at one end and an acidic pocket
at the other. The structure supports a model whereby the transition of native C3
to its functionally active state involves the disruption of a complementary
domain interface and provides insight into the basis for the interaction between
C3d and CR2.
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Figure 2.
Fig. 2. Sequence conservation of C3d. (A) Multiple sequence
alignment of selected species of C3d and human C4d (B isotype)
(21). Residues shaded in yellow are at least 90% buried in the^
C3d structure, and those shaded in red are residues composing
the contiguous surface patch labeled in (B). Numbers correspond^
to the degree of conservation in C3d sequences only: 0 (not
conserved) to A (highly conserved), as determined by the program
AMAS (32). In human C4d, approximately 75% of the core residues,
as well as the putative domain interface residues, are highly
conserved^ [a conservation index (cons. index) of 7 or higher
when included^ in the AMAS calculation], which suggests that it
will adopt a^ similar fold and possess the analogous domain
interface. The helical segments in human C3d are indicated by
blue cylinders. [The figure^ was prepared with ALSCRIPT (35).]
(B) Mapping of residue^ conservation as determined in (A) onto
the surface of C3d; white^ (not conserved) to progressively
darker red (highly conserved). [The figure was prepared with
GRASP (36).] The conserved patch includes most of the surface
apolar residues shown in Fig. 1C.
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Figure 3.
Fig. 3. Stereo view of an electrostatic surface rendition of
C3d, showing the acidic pocket on the concave end of the
molecule. Acidic^ and basic residues are colored red and blue,
respectively. Labeled^ are the surface-exposed residues that
form the pocket. The contour level is at ±10 kT.
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The above figures are
reprinted
by permission from the AAAs:
Science
(1998,
280,
1277-1281)
copyright 1998.
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