Raman, infrared, and circular dichroism spectroscopic studies on metallothionein: a predominantly "turn"-containing protein

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Abstract
Raman and IR spectra of rabbit liver metallothionein 1 (MT-1) containing 7 mol of either cadmium or zinc ions reveal high-lying amide III bands between 1290 and 1330 cm-1, indicative of .beta.-turns. A comparison of the splitting pattern in the amide III region below 1290 cm-1 and in the amide I band between 1600 and 1700 cm-1, with the normal-mode calculations of Lagant et al. [Lagant, P., Vergoten, G., Fleury, G., and Loucheux-Lefebvre, M. (1984a) Eur. J. Biochem. 139,137-148; Lagant, P., Vergoten, G., Fleury, G., and Loucheux-Lefebvre, M. (1984b) Eur. J. biochem. 1939, 149-154; Lagant, P., Vergoten, G., Fleury, G., and Loucheux-Lefebvre, M. (1984c) J. Raman Spectrosc. 15, 421-423] and Krimm and Bandekar [Krimm, S., and Bandekar, J. (1980) Biopolymers 19, 1-29], suggests that metal-bound (holo) MT-1 consists largely of .beta.-turns of type II. In contrast, the metal-free (apo) protein displays a predominantly unordered conformation. The Raman spectra of the holoproteins below 1000 cm-1 are characterized by several unusual skeletal stretching and bending modes. The spectral patter between 760 and 800 cm-1 in conjunction with the splitting of the amide I band agrees closely with the normal-mode calculations of Lagant et al. (1984b) on model peptides and is indicative of the presence of type III .beta.-turns (or 310-helical segments) in MT-1. The good agreement between the vibrational spectroscopic results presented here on MT-1 and the 2D NMR solution structure and X-ray crystal structure data on MT-2 [Braun, G., Wagner, G., Worgotter, E., Vasak, M., Kagi, J.H.R., and Wuthrich, K. (1986) J. Mol. biol. 187, 125-129; Wagner, G., Neuhaus, D., Worgotter, E., Vasak, M. Kagi, J.H.R., and Wuthrich, K. (1986) J. Mol. Bio. 187, 131-135; Furey, W.F., Robbins, A.H., Clancy, L.L., Winge, D.R., Wang, B.C., and Stout, C.D. (1986) Science (Washington, D.C.) 231, 704-710] demonstrates that both isoforms of the protein assume nearly identical folding patterns.