NMR-STUDY OF THE INTERACTION BETWEEN THE B-DOMAIN OF STAPHYLOCOCCAL PROTEIN-A AND THE FC PORTION OF IMMUNOGLOBULIN-G

The solution structure of the B domain of staphylococcal protein A (FB ) complexed with the Fc fragment of immunoglobulin G (IgG) is reported . A previous NMR analysis has shown that in solution FB is composed of a bundle of three or-helices, helix I, helix II, and helix III [Gouda , H., Torigoe, H., Saito, A., Sate, M., Arata, Y., and Shimada, I. (19 92) Biochemistry 31: 9665-9672]. In contrast, the crystal structure of FB in the FB-Fc complex lacks helix III. Uniformly N-15-and N-15/C-13 -labeled FB were prepared, and the backbone C-13 resonances were assig ned. The spectral data obtained in the present study indicated that in solution all three helices including helix III are preserved in the F B-Fc complex. The mode of interaction of FB with the Fc fragment was d iscussed on the basis of the combined data of hydrogen-deuterium excha nge experiments and H-1-N-15 correlation spectroscopy. It was conclude d that a contiguous surface shaped by F14, Y15, E16, L18, and H19 in h elix I, and N29, Q33, L35, and K36 in helix II is responsible for the binding.