Comparison of model and nuclear magnetic resonance structures for the human inflammatory protein C5a

The model structure previously proposed for human C5a, based upon the crystal structure of the homologous protein human C3a, is compared to the solution structure of human C5a recently determined by nuclear magnetic resonance (NMR) methods in our laboratory. The general folding and helix topography of the C5a protein were modeled very well. The N-terminus, which is disordered in the C3a crystal, was correctly predicted in the C5a model both as to its being a helix and as to its docking site on the rest of the molecule. On the other hand, the NMR data show that the biologically important C-terminal residues are disordered in solution, unlike the model and the C3a crystal structure where this region was helical.