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

Abstract
15N nuclear magnetic resonance (NMR) studies of the B domain (FB) of Staphylococcus protein A, which is uniformly labeled with 15N, are reported. The α 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 the 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.