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Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892 Received December 7, 1989; Revised Manuscript Received February 28, 1990 abstract: A novel approach is described for obtaining sequential assignment of the backbone* H, 13C, and 15N resonances of largerproteins. The approach is demonstrated for the protein calmodulin (16.7 kDa), uniformly (~ 95%) labeled with 15N and 13C. Sequential assignment of the backbone residues by standard methods was not possible because of the very narrow chemical shift distribution range of both NH and C “H protons in this largely a-helical protein. We demonstrate that the combined use of four new types of heteronuclear 3D NMR spectra together with the previously described HOHAHA-HMQC 3D experiment [Marion, D., et al.(1989) Biochemistry 28, 6150-6156] can provide unambiguous sequential assignment of protein …