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  • 1
    ISSN: 1573-4943
    Keywords: Botulinum ; circular dichroism ; FT-IR ; secondary structures ; methanol ; neurotoxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two pharmacologically similar but antigenically distinct botulinum neurotoxins, types A and E with a 1000-fold difference in their toxicity, were examined for nonpolar solvent-induced changes in secondary structures and polypeptide foldings to understand their structural differences and their comparative responsiveness/susceptibility to solvent perturbation. Analysis of far UV circular dichroic spectra in aqueous buffer for types A and E neurotoxins yielded the following: the α-helix contents were 27 and 20%; the β-sheets were 36 and 44%, the β-turns were 6.0 and 0%, and the random coils were 31 and 36%, respectively. Fourier transform infrared spectra, obtained by using attenuated total reflection technique, indicated high content of α-helix and β-pleated sheet structures for both neurotoxins as judged by strong bands at 1651 and 1633 cm−1 in the amide I frequency region and bands at 1314 and 1245 cm−1 in the amide III frequency region. The peak height ratio of 1314 and 1245 cm−1 bands, suggests that the type A neurotoxin has slightly higher α-helical content than the type E neurotoxin. These observations are consistent with the secondary structures estimated from far UV circular dichroic spectra. Fourier transform infrared spectra of the neurotoxins, exposed to methanol, showed sharp increases of the 1651 cm−1 band and a significant increase in the height of the 1314 cm−1 band, suggesting increases in the α-helical contents of the proteins. The changes were more in the type A than in the type E neurotoxin. The changes were reversible upon reexposure of the proteins to the aqueous buffer. Second derivative absorption spectroscopy demonstrated that methanol also induced changes in the degree of Tyr exposure to solvent. The results are discussed in terms of structural differences between the single and dichain neurotoxins and in terms of their mode of action.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 85 (1989), S. 67-73 
    ISSN: 1573-4919
    Keywords: botulinum ; circular dichroism ; fluorescence ; quantum yield ; secondary structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The secondary and tertiary structural features of botulinum neurotoxin (NT) serotype A, a dichain protein (Mr 145 000), and its two subunits, the heavy (H) and light (L) chains (Mr 97 000 and 53 000, respectively) were examined using circular dichroism and fluorescence spectorscopy. Nearly 70% of the amino acid residues in each of the three polypeptide preparations were found in ordered structure (sum of α helix, β sheet and β turns). Also, the α helix, β sheet, β turns and random coil contents of the dichain NT were nearly equal to the weighted mean of each of these secondary structure parameters of the L and H chains; e.g., sum of α helix of L chain (22%) and H chain (18.7%), as weighted mean, 19.8% was similar to that of NT (20%). These agreements suggested that the secondary structures of the subunits of the dichain NT do not significantly change when they are separated as isolated L and H chains. Fluorescence emission maximum of L chain, 4 nm less (blue shift) than that of H chain, suggested relatively more hydrophobic environment of fluorescent tryptophan residue(s) of L chain. Tryptophan fluorescence quantum yields of L chain, H chain and the NT, 0.072, 0.174 and 0.197, respectively, suggested that a) an alteration in the micro-environment of the tryptophan residues was possibly caused by interactions of L and H chain subunits of the NT and b) quantum yields for L and H chains were altered when they are together as subunits of the NT. Possible implications of structural features of the L and H chains, their interactions and the molecular mechanism of action of botulinum NT are assessed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 86 (1989), S. 87-95 
    ISSN: 1573-4919
    Keywords: botulinum neurotoxin ; derivative spectra ; tyrosine exposure ; secondary structure ; circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Botulinum neurotoxin (NT) serotypes A, B and E differ in microstructure and biological activities. The three NTs were examined for secondary structure parameters (α-helix, β-sheet, β-turn and random coil content) on the basis of circular dichroism; degree of exposed Tyr residues (second derivative spectroscopy) and state of the Trp residues (fluorescence and fluorescence quantuin yield). The proteins are high in β-pleated sheet content (41–44%) and low in α-helical content (21–28%). About 30–36% of the amino acids are in random coils. The β-sheet contents in the NTs are similar irrespective of their structural forms (i.e. single or dichain forms) or level of toxicity. About 84%, 58% and 61% of Tyr residues of types A, B, and ENT, respectively, were exposed to the solvent (pH 7.2 phosphate buffer). Although the fluorescence emission maximum of Trp residues of type B NT was most blue shifted (331 nm compared to 334 for types A and E NT, and 346 nm for free tryptophan) the fluorescence quantum yields of types A and B were similar and higher than type E. In general the NTs have similar secondary (low α-helix and high β-sheets) and tertiary (exposed tyrosine residues and tryptophan fluorescence quantum yield) structures. Within this generalized picture there are significant differences which might be related to the differences in their biological activities.
    Type of Medium: Electronic Resource
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