Conformational studies on the N-linked carbohydrate chain of bromelain.

1H- and 13C-NMR assignments for the carbohydrate part of the glycopeptide alpha-D-Man-(1----6)-[beta-D-Xyl-(1----2)]-beta-D-Man-(1----4)-beta-D- GlcNAc-(1----4)-[alpha-L-Fuc-(1----3)]-beta-D-GlcNAc-(1----N)-Asn approximately, derived from the proteolytic enzyme bromelain (EC 3.4.22.4), have been obtained using homo- and heteronuclear correlation spectroscopy, two-dimensional homonuclear Hartmann-Hahn and nuclear Overhauser enhancement experiments. A conformational model for the carbohydrate chain, deduced from the NMR data and consistent with hard-sphere exo-anomeric calculations shows that the rotamer population about the C-5--C-6 bond of beta-Man is restricted to the P omega = 180 rotamer, mainly.