| Two-dimensional proton NMR experiments have been used to sequentially assign resonances to all of the peptide backbone protons of turkey ovomucoid third domain (OMTKY3) except those of the N-terminal S-amino group whose signal was not resolved owing to exchange with the solvent. Assignments also have been made for more than 80% of the side-chain protons. Two-dimensional chemical shift correlated spectroscopy (COSY), relayed coherence transfer spectroscopy (RELAY), and two-dimensional homonuclear Hartmann-Hahn spectroscopy (HOHAHA) were used to identify the spin systems of almost half of the residues prior to sequential assignment. Assignments were based on two-dimensional nuclear Overhauser enhancements observed between adjacent residues. The secondary structure of OMTKY3 in solution was determined from additional assigned NOESY cross-peaks; it closely resembles the secondary structure determined by single-crystal X-ray diffraction of OMTKY3 in complex with Streptomyces griseus proteinase B (Fujinaga, M., Read, R. J., Sielecki, A., Ardelt, W., Laskowski, M., Jr., and James, M. N. G. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 4868-4872). Through studies of the pH dependence for amide proton chemical shifts, we have confirmed pK... |
