Sequential 1H NMR assignments and secondary structure identification of human ubiquitin.

1H NMR assignments of human ubiquitin (76 amino acids, Mr 8565) have been made by a combination of DQF-COSY, DQF-RELAY, NOESY, DQ, and isotropic mixing experiments. Complete NH, C alpha H, and C beta H assignments were obtained; resonances not yet assigned are the side-chain amides of Q-40, Q-41, Q-49, N-60, and Q-62 and the peripheral protons (C gamma H and outward) of M-1 and K-27. A total of 558 out of 579 (96%) potentially observable protons were assigned. Particular attention was directed toward obtaining complete assignments of the aliphatic residues (seven Ile, nine Leu, four Val) since these residues form an extensive hydrophobic core and NOEs from these residues are invaluable for structure calculations. The secondary structure elements were also identified from the sequential NOE data and differ slightly in description from the published 2.8 A resolution crystal structure [Vijay-Kumar, S., Bugg, C. E., Wilkinson, K. D., & Cook, W. J. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 3582-3585]; the NMR data suggest that residues 48-50 form a short fifth strand in the beta-sheet and that residues 56-61 form a helical turn. The sequential assignment results presented here are in agreement with the main chain directed assignments presented in the preceding paper [Di Stephano, D., & Wand, A. J. (1987) Biochemistry (preceding paper in this issue)].