A 13C Nuclear Magnetic Resonance Study of Histone H1 in 2-ChIoroethanol and Aqueous Solutions. Identification of Peaks Characteristic of Secondary Folding1

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Abstract
A 13 C NMR study of calf thymus histone HI in both aqueous solution and 2-chlo-roethanol solution was performed to clarify the folding behavior in these systems. To ascertain the general trend of displacements of 13 C shifts upon folding in an enhanced manner, the latter solvent was employed since it is known to increase the amount of α-helix content in histone to about 50%. Generally, upfield displacements of C β signals (up to 1.4 ppm) were clearly identified as helix-induced peaks, although displacements of C α signals, which might be much larger, were not easily distinguished because of overlap of several broadened signals with reduced peak intensities. In particular, we found that the upfield displacement of Ala C β , by 1.1 ppm, is ah excellent probe to monitor the presence of α-helix conformation in both 2-chloroethanol and aqueous solutions. This upfield displacement of the C β signal in α-helix segment is consistent with our previous findings for a number of model polypeptides by ordinary and solid-state high resolution 13 C NMR spectroscopy. Further, we observed that 13 C peaks of several residues (Tyr, Ser, Leu, Ile, and Val) were suppressed as a result of specific folding of HI in the presence of NaCl in aqueous solution. Thus, it appears that several tightly-folded segments whose 13 C signals were considerably broadened are located in the central core portion.