The secondary structure of human recombinant interleukin-4 (IL-4) has been investigated by three-dimensional (3D) IsNand I3C-edited nuclear Overhauser (NOE) spectroscopy on the basis of the 'H, ISN, and 13C assignments presented in the preceding paper [Powers, R., Garrett, D. S., March, C. J., Frieden, E. A" Gronenborn, A. M., & Clore, G. M. (1992) Biochemistry (preceding paper in this issue)]. Based on the NOE data involving the NH, CaH, and C@H protons, as well as 3Jma coupling constant,

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... exchange, and 13Ca and I3CB secondary chemical shift data, it is shown that IL-4 consists of four long helices (residues 9-21, 45-64, 74-96, and 113-129), two small helical turns (residues 27-29 and 67-70), and a mini antiparallel @-sheet (residues 32-34 and 110-1 12). In addition, the topological arrangement of the helices and the global fold could be readily deduced from a number of long-range interhelical NOES identified in the 3D I3C-edited NOE spectrum in combination with the spatial restrictions imposed by three disulfide bridges. These data indicate that the helices of interleukin-4 are arranged in a left-handed four-helix bundle with two overhand connections. Abbreviations: IL-4, interleukin-4 (the numbering scheme used in the present paper includes the four-residue sequence Glu-Ala-Glu-Ala at the N-terminus of the recombinant protein which is not part of the natural human IL-4; the natural IL-4 sequence therefore starts at residue 5); NMR, nuclear magnetic resonance; CD, circular dichroism; IgE, immunoglobulin E; NOE, nuclear Overhauser effect; NOESY; nuclear Overhauser enhancement spectroscopy; HMQC, heteronuclear multiple-quantum coherence; 3D, three dimensional; 4D, four dimensional; TPPI, time-proportional phase incrementation. 0