Characterization of a membrane binding loop leads to engineering botulinum neurotoxin B with improved therapeutic efficacy

Botulinum neurotoxins (BoNTs) are a family of bacterial toxins with seven major serotypes (BoNT/A–G). The ability of these toxins to target and bind to motor nerve terminals is a key factor determining their potency and efficacy. Among these toxins, BoNT/B is one of the two types approved for medical and cosmetic uses. Besides binding to well-established receptors, an extended loop in the C-terminal receptor-binding domain (H_C) of BoNT/B (H_C/B) has been proposed to also contribute to toxin binding to neurons by interacting with lipid membranes (termed lipid-binding loop [LBL]). Analogous loops exist in the H_Cs of BoNT/C, D, G, and a chimeric toxin DC. However, it has been challenging to detect and characterize binding of LBLs to lipid membranes. Here, using the nanodisc system and biolayer interferometry assays, we find that H_C/DC, C, and G, but not H_C/B and H_C/D, are capable of binding to receptor-free lipids directly, with H_C/DC having the highest level of binding. Mutagenesis studies demonstrate the critical role of consecutive aromatic residues at the tip of the LBL for binding of H_C/DC to lipid membranes. Taking advantage of this insight, we then create a “gain-of-function” mutant H_C/B by replacing two nonaromatic residues at the tip of its LBL with tryptophan. Cocrystallization studies confirm that these two tryptophan residues do not alter the structure of H_C/B or the interactions with its receptors. Such a mutated H_C/B gains the ability to bind receptor-free lipid membranes and shows enhanced binding to cultured neurons. Finally, full-length BoNT/B containing two tryptophan mutations in its LBL, together with two additional mutations (E1191M/S1199Y) that increase binding to human receptors, is produced and evaluated in mice in vivo using Digit Abduction Score assays. This mutant toxin shows enhanced efficacy in paralyzing local muscles at the injection site and lower systemic diffusion, thus extending both safety range and duration of paralysis compared with the control BoNT/B. These findings establish a mechanistic understanding of LBL–lipid interactions and create a modified BoNT/B with improved therapeutic efficacy.

Botulinum neurotoxins are a family of bacterial toxins, some of which are approved for medical and cosmetic uses. This study shows that introducing aromatic residues to a lipid binding loop improved therapeutic efficacy of botulinum neurotoxin B by enhancing its ability to bind to lipid membranes at motor nerve terminals.

Purification and Characterization of Recombinant Botulinum Neurotoxin Serotype FA, Also Known as Serotype H

We have purified and characterized recombinant botulinum neurotoxin serotype FA (BoNT/FA). This protein has also been named as a new serotype (serotype H), but the classification has been controversial. A lack of well-characterized, highly pure material has been a roadblock to study. Here we report purification and characterization of enzymatically active, and of inactive nontoxic, recombinant forms of BoNT/FA as tractable alternatives to purifying this neurotoxin from native Clostridium botulinum. BoNT/FA cleaves the same intracellular target proteins as BoNT/F1 and other F serotype BoNTs; the intracellular targets are vesicle associated membrane proteins (VAMP) 1, 2 and 3. BoNT/FA cleaves the same site in VAMP-2 as BoNT/F5, which is different from the cleavage site of other F serotype BoNTs. BoNT/FA has slower enzyme kinetics than BoNT/F1 in a cell-free protease assay and is less potent at inhibiting ex vivo nerve-stimulated skeletal muscle contraction. In contrast, BoNT/FA is more potent at inhibiting neurotransmitter release from cultured neurons.

Role of ATP hydrolysis in the DNA translocase activity of the bovine papillomavirus (BPV-1) E1 helicase

The E1 protein of bovine papillomavirus type-1 is the viral replication initiator protein and replicative helicase. Here we show that the C-terminal approximately 300 amino acids of E1, that share homology with members of helicase superfamily 3 (SF3), can act as an autonomous helicase. E1 is monomeric in the absence of ATP but assembles into hexamers in the presence of ATP, single-stranded DNA (ssDNA) or both. A 16 base sequence is the minimum for efficient hexamerization, although the complex protects approximately 30 bases from nuclease digestion, supporting the notion that the DNA is bound within the protein complex. In the absence of ATP, or in the presence of ADP or the non-hydrolysable ATP analogue AMP-PNP, the interaction with short ssDNA oligonucleotides is exceptionally tight (T(1/2) > 6 h). However, in the presence of ATP, the interaction with DNA is destabilized (T(1/2) approximately 60 s). These results suggest that during the ATP hydrolysis cycle an internal DNA-binding site oscillates from a high to a low-affinity state, while protein-protein interactions switch from low to high affinity. This reciprocal change in protein-protein and protein-DNA affinities could be part of a mechanism for tethering the protein to its substrate while unidirectional movement along DNA proceeds.

Indication for psychotherapy in offspring of a parent affected by a chronic somatic disease (e.g. multiple sclerosis)

Based on the transcripts of video-recorded, semi-structured interviews with 41 offspring (aged 6-18 years) of parents with multiple sclerosis, we evaluated the indication for psychotherapy. These results were then compared with the previously determined coping ability of each child/adolescent. Psychotherapy was indicated for 22 out of the 41 children/adolescents. There was a significant relation between the indication for psychotherapy and the children's inability to cope with the parental disease. The present findings confirm the risk of mental health problems in children of somatically ill parents. In our sample, half of the children and adolescents were estimated to benefit from individual psychotherapy, which might enhance their ability to cope with the parental illness.

Role of CYP1A2 in hepatic sequestration of dioxin: studies using CYP1A2 knock-out mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin), most potent of the polyhalogenated aromatic hydrocarbons, has been studied in a variety of genetically normal species. Transgenic mice lacking a cytochrome P450 1A2 gene were used to study the influence of the CYP1A2 gene on the hepatic sequestration and distribution of TCDD, 4-PeCDF (2,3,4,7,8-pentachlorodibenzofuran; dioxin-like compound), and PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl; non-dioxin-like PCB (polychlorinated biphenyl)). The knock-out mice were compared to their age-matched lineage strains of C57BL/6N (1A2+/+; Ah(b)) and 129/Sv (1A2+/+; Ah(d)) for each compound. As demonstrated by the liver-to-adipose tissue (L/F) concentration ratios, there was no hepatic sequestering of TCDD and 4-PeCDF in the transgenic knock-out mice.