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. 2019 Feb 7;9:1634. doi: 10.1038/s41598-018-37647-8

Figure 2.

Figure 2

Comparison of the BoNT-LC with homologous domains from BoNT-like toxins and M91 family proteases. (a) Phylogenetically, BoNTs and divergent BoNT homologs group distinct from distantly related peptidase M91 sequences. Statistical support for the tree is indicated as maximum likelihood bootstrap value and Bayesian posterior probability (percentage), respectively. Structural comparison of BoNT/A (PDB 1XTG) (iii) with structural models of Chryseobacterium Cp1 (ii) and E. coli NleD (i) reveals two regions that are unique to BoNTs and BoNT-like proteins: the lower alpha-helical region, which interacts directly with SNARE substrates, and the C-terminal region that plays a role in catalytic product removal. (b) M91 family peptidase domains (i), divergent BoNT homologs (ii), and BoNT-LCs (iii) have key conserved sequence features. These include the HExxH zinc-coordinating and catalytic residues, the third zinc ligand E261, and the active site-refining E350 and RxxY motif. As depicted in the multiple alignment, two insertion regions appear unique to BoNTs and divergent BoNT homologs, shown in teal and purple respectively. The identities of proteins labeled 1-14 are: 1 – WP_037712107.1, Streptomyces sp. AA4; 2 – EFL04418.1, Streptomyces sp. AA4; 3 – WP_083906476.1, Acaricomes phytoseiuli; 4 – GAO13068.1, Streptomyces sp. NBRC_110027, 5 – WP_055473237.1, Streptomyces pathocidini; 6 – WP_070931163.1, Mycobacterium chelonae; 7 – WP_034681281.1, Chryseobacterium piperi; 8 – WP_034687877.1, Chyrseobacterium piperi; 9 - WP_034687193.1, Chryseobacterium piperi; 10 – WP_034687872.1, Chryseobacterium piperi; 11 – WP_027699549.1, Weissella oryzae; 12 – WP_086311652.1, Enterococcus BoNT/En; 13 – BAQ12790.1, BoNT/X; 14 – ABS38337.1, BoNT/A1.