Structure at 1.44 A resolution of an N-terminally truncated form of the rat serum complement C3d fragment.
Complement component C3 plays a key role in the complement-mediated immune defence, and occupies a central position within the complement cascade system. One of its degradation products, C3dg, was purified from rat serum and crystallised in two different crystal forms as N-terminally truncated fragment. Despite the truncation and the lack of a significant portion of the N-terminus as compared to C3d, the structure of the fragment is highly similar to that of recombinant human C3d (Nagar et al., Science 280 (1998) 1277-1281). Structural details of the reactive site have been obtained, suggesting a possible mode of thioester bond formation between Cys-1010 and Gln-1013 and thioester bond cleavage in the transacylation reaction involving His-1126. The truncation at the N-terminus of C3d leads to the exposure of a surface of the molecule that favours dimerisation, so that in both crystal forms, the fragment is present as a dimer, with monomers related by a two-fold axis.
Zanotti
G
G
Department of Organic Chemistry and Biopolymer Research Center, University of Padova, Italy. zanotti@chor.unipd.it
Bassetto
A
A
Battistutta
R
R
Folli
C
C
Arcidiaco
P
P
Stoppini
M
M
Berni
R
R
D000818:Animals; D015933:Complement C3d / Q000737:chemistry* / Q000276:immunology / Q000302:isolation & purification; D003460:Crystallization; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments; D011487:Protein Conformation; D051381:Rats
D010446:Peptide Fragments; D015933:Complement C3d