A mixed β-turn and β-sheet structure for bovine tooth enamel amelogenin: Raman spectroscopic evidence
✍ Scribed by Siding Zheng; Antony T. Tu; V. Renugopalakrishnan; E. Strawich; Melvin J. Glimcher
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1987
- Tongue
- English
- Weight
- 316 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Amelogenins, a class of sparsely phosphorylated hydrophobic proteins characterized by a high concentration of Pro, Gln, Leu, and His have been implicated in the mineralization of tooth Recently a unique primary structure of bovine tooth enamel amelogenin was reported by Takagi et al.,3 characterized by repeating tripeptides Gln-Pro-X near the C-terminal region. Recent CD, Fourier transform infrared, and Chou-Fasman predictions of the secondary structure4 of the lower molecular weight component, M, -19.35 kD5 have revealed that the protein has a low a-helical content, and high /?-turn and /?-sheet composition. Molecular modeling and mechanics calculations of a 27-residue polypeptide fragment near the C-terminal from G l r ~, , ~ to Leu,,, (N. Pattabiraman, V. Renugopalakrishnan, E. Strawich, M. J.
Glimcher, and R. Langridge, submitted) have clearly highlighted the role of /?-turns in the secondary structure of this protein. To obtain further evidence of the proposed secondary structure, we have undertaken Raman spectroscopic studies of amelogenin. Recently many peptides known to have /?-turn from x-ray and nmr have been examined by Raman spectroscopy,6 and therefore there is sufficient Raman data in the literature t o elucidate p-turn conformation in polypeptides and proteins. Raman spectroscopic studies provide complimentary information to CD and FT-IR studies on the polypeptide backbone conformation. Theoretically expected amide I and I11 frequencies of /?-turns have been discussed by Lagant et al.7.' and Krimm and Seaton (see Refs. 9 and 10, and other references cited therein). In addition, Raman spectra provide information on the side-chain conformations of certain aromatic amino acid residues.
EXPERIMENTAL
Preparation of the major highest molecular weight bovine amelogenin from developing premolar teeth has been previously de~cribed.~ Raman spectra were obtained with a Spex Industries Ramalog 5 Raman spectrometer equipped with the computer Spex SCAMP. A sample of amelogenin in aqueous solution was placed in a capillary tube and was illuminated using the 514.5-nm excitation line of an argon-ion laser (Spectraphysics model SP-164). A green interference filter was used to eliminate plasma lines of the laser. The signal was averaged from 10 scans by SCAMP data acquisition processor. Deuterated amelogenin was made by dissolving amelogenin in D,O and then by lyophilization to recover the solid. The sample was again dissolved in D,O for