3-DIMENSIONAL SOLUTION STRUCTURE OF THE N-TERMINAL RECEIVER DOMAIN OFNTRC

NTRC is a transcriptional enhancer binding protein whose N-terminal do main is a member of the family of receiver domains of two-component re gulatory systems. Using 3D and 4D NMR spectroscopy, we have completed the H-1, N-15 and C-13 assignments and determined the solution structu re of the N-terminal receiver domain of the NTRC protein. Determinatio n of the three-dimensional structure was carried out with the program X-PLOR (Brunger, 1992) using a total of 915 NMR-derived distance and d ihedral angle restraints. The resultant family of structures has an av erage root mean square deviation of 0.81 Angstrom from the average str ucture for the backbone atoms involved in well-defined secondary struc ture. The structure is comprised of five alpha-helices and a five-stra nded parallel P-sheet, in a ((beta/alpha)(5))5 topology. Comparison of the solution structure of the NTRC receiver domain with the crystal s tructures of the homologous protein CheY in both the Mg2+-free and Mg2 +-bound forms [Stock, A. M., Mottonen, J. M., Stock, J. B., and Schutt , C. E. (1989) Nature 337, 745-749; Volt, K., and Matsumura, P. (1991) J. Biol. Chem. 296, 15511-15519; Stock, A. M., Martinez-Hackert, E., Rasmussen, B. F., West, A. H., Stock, J. B., Ringe, D., and Petsko, G. A. (1993) Biochemistry 32, 13375-13380; Bellsolell, L., Prieto, J., S errano, L., and Cell, M. (1994) J. Mel. Biol. 238, 489-495] reveals a very similar fold, with the only significant difference occurring in t he positioning of helix 4 relative to the rest of the protein. Examina tion of the conformation of consensus residues of the receiver domain superfamily [Volz, K. (1993) Biochemistry 32, 11741-11753] in the stru ctures of the NTRC receiver domain and CheY establishes the structural importance of residues whose side chains are involved in hydrogen bon ding or hydrophobic core interactions. The importance of some nonconse nsus residues which may be conserved for their ability to fulfill heli x capping roles is also discussed.