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Structural diversity of amyloid fibril formed in human calcitonin as revealed by site‐directed 13 C solid‐state NMR spectroscopy
Author(s) -
Naito Akira,
Kamihira Miya,
Inoue Ryozo,
Saitô Hazime
Publication year - 2004
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1323
Subject(s) - chemistry , nuclear magnetic resonance spectroscopy , solid state nuclear magnetic resonance , fibril , spectroscopy , amyloid fibril , crystallography , solid state , amyloid (mycology) , stereochemistry , nuclear magnetic resonance , amyloid β , biochemistry , inorganic chemistry , medicine , disease , pathology , physics , quantum mechanics
Fibril formation in human calcitonin (hCT) from aqueous solution at pH 4.1 was examined and compared with those at pH 3.3 and 7.5 corresponding to three different net charges by means of site‐directed 13 C solid‐state NMR spectroscopy. Notably, the observed 13 C chemical shifts and lineshapes of the 13 C CP/MAS spectra differed substantially among fibrils prepared at different pHs. It was found that antiparallel β‐sheet structures were formed at pH 7.5 and 4.1 in the central core regions. In the C‐terminal region, random coils were formed at both pH 7.5 and 4.1, although the random coil region at pH 4.1 was larger than that at pH 7.5. Fibrillation kinetics analyzed by a two‐step autocatalytic reaction mechanism showed that the rate constants k 1 and k 2 for nucleation and maturation reactions of the fibril formation, respectively, were separately determined and the values correlated well with the net positive charges of Lys 18 and His 20 rather than the existence of a negative charge of Asp 15 . Further, an attempt was made to assess interatomic distances between amide nitrogen and carbonyl carbon of neighboring chains of 13 C, 15 N‐labeled hCT and a model pentapeptide by 13 C REDOR measurements by taking into account its dipolar interaction analyzed by the 3 spin system proposed previously. A unique chain packing of the antiparallel β‐sheets was proposed as a dominant fibril structure, although the possibility of a contribution of chain packing consisting of sliding one or two residues perpendicular to the fibril direction cannot be ruled out. In addition, it appears that the phenyl rings of Phe 16 are aligned on the same side of the β‐sheet and make the β‐sheet stable by forming π–π interactions between the β‐strands. Copyright © 2004 John Wiley & Sons, Ltd.