Secondary structure of complement component C3a anaphylatoxin in solution as determined by NMR spectroscopy: differences between crystal and solution conformations.
Two-dimensional 1H NMR investigations were used to locate elements of regular secondary structure in the human complement protein C3a (the des-Arg77 derivative) in solution. The results were compared to a refined crystal structure based on the 3.2-A resolution structure of des-Arg77-C3a [Huber, R., Scholze, H., Paques, E. P. & Deisenhofer, J. (1980) Hoppe-Seyler's Z. Physiol. Chem. 361, 1389-1399]. In excellent agreement with the x-ray data, helices occur in the regions of residues 17-28 and 36-43 in solution. In contrast to the x-ray data, where a third long helix was found from residue 47 to residue 73, the solution data show a shorter helix in the region from residue 47 to residue 66, followed by a transition range at positions 67-70, leading into a six-residue carboxyl-terminal peptide in dynamic random coil conformation. At the amino terminus, a well-defined helix is observed in solution for the residues 8-15 region, which, like the carboxyl terminus, gradually changes to dynamic random coil toward the end of the polypeptide chain. This is at variance with the x-ray data as well, in which residues 13-15 are nonhelical and no electron density could be assigned to the first 12 residues due to disorder.
Nettesheim
D G
DG
Pharmaceutical Discovery Division, Abbott Laboratories, Abbott Park, IL 60064.
Edalji
R P
RP
Mollison
K W
KW
Greer
J
J
Zuiderweg
E R
ER
D000706:Anaphylatoxins; D003176:Complement C3; D015926:Complement C3a; D003182:Complement C5; D015936:Complement C5a; D003460:Crystallization; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides; D011487:Protein Conformation; D012996:Solutions; D014961:X-Ray Diffraction
D000706:Anaphylatoxins; D003176:Complement C3; D003182:Complement C5; D010455:Peptides; D012996:Solutions; D015926:Complement C3a; D015936:Complement C5a