Two- and three-dimensional proton NMR studies of apo-neocarzinostatin

Neocarzinostatin (NCS) is an antitumor protein from Streptomyces carzinostaticus that is identical in apo-protein sequence with mitomalcin (MMC) from Streptomyces malayensis. We describe the use of apo-NCS as a model system for applying combined two- and three-dimensional (2D and 3D) proton NMR spectroscopy to the structure determination of proteins (Mr greater than 10K) without isotope labeling. Strategies aimed at accurately assigning overlapped 2D cross-peaks by using semiautomated combined 2D and 3D data analysis are developed. Using this approach, we have assigned 99% of the protons, including those of the side chains, and identified about 1270 intra- and interresidue proton-proton interactions (fixed distances are not included) in apo-NCS. Comparing our results with those reported recently on 2D NMR studies of apo-NCS [Adjadj, E., Mispelter, J., Quiniou, E., Dimicoli, J.-L., Favadon, V., & Lhoste, J.-M. (1990) Eur. J. Biochem. 190, 263-271; Remerowski M. L., Glaser, S. J., Sieker, L., Samy, T. S. A., & Drobny, G. P. (1990) Biochemistry 29, 8401-8409] demonstrated advantages of proton 3D NMR spectroscopy in protein spectral assignments. We are able to obtain more complete proton resonance and secondary structural assignments and find several misassignments in the earlier report. Strategies utilized in this work should be useful for developing automation procedures for spectral assignments.