15N nuclear magnetic resonance studies of the B domain of staphylococcal protein A: sequence specific assignments of the imide 15N resonances of the proline residues and the interaction with human immunoglobulin G.

15N nuclear magnetic resonance (NMR) studies of the B domain (FB) of Staphylococcus protein A, which is uniformly labeled with 15N, are reported. The alpha CH(i)-15N(i) connectivity in the 1H-15N HMBC spectrum and the 13C(i-1)-15N(i) spin coupling in the 15N spectrum of a 13C-, 15N-doubly labeled FB were used to establish the assignments of the imide 15N resonances for all three Pro residues that exist in FB. Addition of human IgG caused a significant downfield shift of the Pro-39 resonance. This result is quite consistent with our previous suggestion that a significant conformation change is induced in the Ser-42-Ala-55 helical region of FB when it is bound to human IgG.