Molecular topography and secondary structure comparisons of botulinum neurotoxin types A, B and E.
Botulinum neurotoxin (NT) serotypes A, B and E differ in microstructure and biological activities. The three NTs were examined for secondary structure parameters (alpha-helix, beta-sheet, beta-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 quantum yield). The proteins are high in beta-pleated sheet content (41-44%) and low in alpha-helical content (21-28%). About 30-36% of the amino acids are in random coils. The beta-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 E NT, 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 alpha-helix and high beta-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.
Singh
B R
BR
Food Research Institute, University of Wisconsin, Madison 53706.
DasGupta
B R
BR
D001905:Botulinum Toxins / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D002942:Circular Dichroism; D009498:Neurotoxins / Q000032:analysis* / Q000378:metabolism; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000032:analysis; D014443:Tyrosine / Q000032:analysis
D009498:Neurotoxins; D014443:Tyrosine; D014364:Tryptophan; D001905:Botulinum Toxins