A structural perspective of the sequence variability within botulinum neurotoxin subtypes A1-A4.
Botulinum neurotoxin (BoNT) is a category A toxin that has been classified within seven serotypes, designated A-G. Recently, it has been discovered that sequence variability occurs in BoNTs produced by serotype A (BoNT/A) variant strains, designated as subtypes A1 and A2, which have significantly different antibody-binding properties. We have therefore made efforts to understand at the molecular level the diversity and its effects on the biological actions of the toxin, including receptor binding, substrate recognition, and catalysis. We provide the results of these studies, including the analysis of two newly sequenced BoNT/A variants, Loch Maree (A3) and 657Ba (A4), and their comparison to A1 and A2. Using sequence analysis, available functional data, molecular modeling, and comparison of models with the crystal structures of BoNT/A1 and the light chain of BoNT/A2, we conclude that these sequence differences within subtypes will impact development of broad-spectrum antibody and small ligand therapeutics, and suggest dissimilarities in binding affinity and cleavage efficiency of the SNAP-25 substrate. In particular, sequence variation in subtypes BoNT/A3 and BoNT/A4 will likely effect alpha-exosite and S1' subsite recognition, respectively.
Arndt
Joseph W
JW
Department of Molecular Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
Jacobson
Mark J
MJ
Abola
Enrique E
EE
Forsyth
Charles M
CM
Tepp
William H
WH
Marks
James D
JD
Johnson
Eric A
EA
Stevens
Raymond C
RC
D000595:Amino Acid Sequence; D001665:Binding Sites; D019274:Botulinum Toxins, Type A / Q000737:chemistry*; D003014:Clostridium botulinum / Q000737:chemistry*; D017124:Conserved Sequence; D005732:Gangliosides / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry
D005732:Gangliosides; D050825:Synaptosomal-Associated Protein 25; D019274:Botulinum Toxins, Type A