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Current status and future directions of botulinum neurotoxins for targeting pain processing.

Pellett S, Yaksh TL, Ramachandran R - Toxins (Basel) (2015)

Bottom Line: However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified.By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics.This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

View Article: PubMed Central - PubMed

Affiliation: Department of Bacteriology, University of Wisconsin, 6340 Microbial Sciences Building, 1550 Linden Dr., Madison, WI 53706, USA. sabine.pellett@wisc.edu.

ABSTRACT
Current evidence suggests that botulinum neurotoxins (BoNTs) A1 and B1, given locally into peripheral tissues such as skin, muscles, and joints, alter nociceptive processing otherwise initiated by inflammation or nerve injury in animal models and humans. Recent data indicate that such locally delivered BoNTs exert not only local action on sensory afferent terminals but undergo transport to central afferent cell bodies (dorsal root ganglia) and spinal dorsal horn terminals, where they cleave SNAREs and block transmitter release. Increasing evidence supports the possibility of a trans-synaptic movement to alter postsynaptic function in neuronal and possibly non-neuronal (glial) cells. The vast majority of these studies have been conducted on BoNT/A1 and BoNT/B1, the only two pharmaceutically developed variants. However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified. By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics. This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

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Botulinum Neurotoxin A1 (BoNT/A1): The 50 kDa light chain (LC) (blue) is linked to the 100 kDa heavy chain (HC) (green, yellow, and red). The HC is functionally divided into the translocation domain (HCN) (green) required for transport of the LC from the endosome into the cell cytosol, and the receptor binding domain (HCR) (yellow and red) through which BoNT binds to the cell surface. Crystal structure image from the Protein databank doi:10.2210/pdb3bta/pdb [36].
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toxins-07-04519-f001: Botulinum Neurotoxin A1 (BoNT/A1): The 50 kDa light chain (LC) (blue) is linked to the 100 kDa heavy chain (HC) (green, yellow, and red). The HC is functionally divided into the translocation domain (HCN) (green) required for transport of the LC from the endosome into the cell cytosol, and the receptor binding domain (HCR) (yellow and red) through which BoNT binds to the cell surface. Crystal structure image from the Protein databank doi:10.2210/pdb3bta/pdb [36].

Mentions: BoNTs are a large family of proteins that are produced by a diverse group of gram positive, spore forming anaerobic bacteria termed Clostridium botulinum and by a few strains of Clostridium butyricum, sporogenes, and baratii [26,27]. At least 40 different subtypes of BoNTs have been described today. The current nomenclature differentiates newly identified BoNTs as novel subtypes based purely on an amino acid difference greater than 2.5% [28], and many more variants exist that are not classified as unique subtypes. The BoNTs are classified into seven serotypes (A though G) based primarily on antigenic specificity [29], and the subtypes within each serotype are denoted by a number following the letter. All BoNTs are modular proteins constructed of a 100 kDa heavy chain (HC) and a 50 kDa light chain (LC) linked by a disulfide bond (Figure 1). The HC is divided into a C-terminal receptor binding domain (HCR) and an N-terminal translocation domain (HCN) [30]. Cell entry by BoNTs proceeds via a multi-step process (Figure 2). The HCR of BoNTs binds to specific protein and ganglioside receptors on the cell surface, leading to endocytosis of the HC-LC complex. In the acidic environment of the endocytic vesicle, protonation causes a conformational shift in the BoNT protein resulting in incorporation of the HC into the endocytic vesicle membrane to form a channel through which the LC is translocated into the cytosol [30,31,32]. The disulfide bond is reduced inside the cell’s cytosol, releasing the LC to refold to an enzymatically active conformation [8,33]. The BoNT LC is a zinc-dependent endoprotease that, once inside the cell, cleaves intracellular SNAREs (soluble N-ethylmaleimide -sensitive-factor attachment protein receptors) at highly specific consensus sites. This cleavage prevents SNARE-mediated protein transport and transmitter release [1,34], which, at the neuromuscular junction, results in a failure of muscle innervation and thus flaccid paralysis. An important characteristic of BoNT LC is that it is capable of persisting in an active configuration in the cytosol for days to months, depending on the BoNT serotype. During that time, the LC continues to cleave its target SNARE, which accounts for the associated duration of action of the respective toxin [8,35].


Current status and future directions of botulinum neurotoxins for targeting pain processing.

Pellett S, Yaksh TL, Ramachandran R - Toxins (Basel) (2015)

Botulinum Neurotoxin A1 (BoNT/A1): The 50 kDa light chain (LC) (blue) is linked to the 100 kDa heavy chain (HC) (green, yellow, and red). The HC is functionally divided into the translocation domain (HCN) (green) required for transport of the LC from the endosome into the cell cytosol, and the receptor binding domain (HCR) (yellow and red) through which BoNT binds to the cell surface. Crystal structure image from the Protein databank doi:10.2210/pdb3bta/pdb [36].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663519&req=5

toxins-07-04519-f001: Botulinum Neurotoxin A1 (BoNT/A1): The 50 kDa light chain (LC) (blue) is linked to the 100 kDa heavy chain (HC) (green, yellow, and red). The HC is functionally divided into the translocation domain (HCN) (green) required for transport of the LC from the endosome into the cell cytosol, and the receptor binding domain (HCR) (yellow and red) through which BoNT binds to the cell surface. Crystal structure image from the Protein databank doi:10.2210/pdb3bta/pdb [36].
Mentions: BoNTs are a large family of proteins that are produced by a diverse group of gram positive, spore forming anaerobic bacteria termed Clostridium botulinum and by a few strains of Clostridium butyricum, sporogenes, and baratii [26,27]. At least 40 different subtypes of BoNTs have been described today. The current nomenclature differentiates newly identified BoNTs as novel subtypes based purely on an amino acid difference greater than 2.5% [28], and many more variants exist that are not classified as unique subtypes. The BoNTs are classified into seven serotypes (A though G) based primarily on antigenic specificity [29], and the subtypes within each serotype are denoted by a number following the letter. All BoNTs are modular proteins constructed of a 100 kDa heavy chain (HC) and a 50 kDa light chain (LC) linked by a disulfide bond (Figure 1). The HC is divided into a C-terminal receptor binding domain (HCR) and an N-terminal translocation domain (HCN) [30]. Cell entry by BoNTs proceeds via a multi-step process (Figure 2). The HCR of BoNTs binds to specific protein and ganglioside receptors on the cell surface, leading to endocytosis of the HC-LC complex. In the acidic environment of the endocytic vesicle, protonation causes a conformational shift in the BoNT protein resulting in incorporation of the HC into the endocytic vesicle membrane to form a channel through which the LC is translocated into the cytosol [30,31,32]. The disulfide bond is reduced inside the cell’s cytosol, releasing the LC to refold to an enzymatically active conformation [8,33]. The BoNT LC is a zinc-dependent endoprotease that, once inside the cell, cleaves intracellular SNAREs (soluble N-ethylmaleimide -sensitive-factor attachment protein receptors) at highly specific consensus sites. This cleavage prevents SNARE-mediated protein transport and transmitter release [1,34], which, at the neuromuscular junction, results in a failure of muscle innervation and thus flaccid paralysis. An important characteristic of BoNT LC is that it is capable of persisting in an active configuration in the cytosol for days to months, depending on the BoNT serotype. During that time, the LC continues to cleave its target SNARE, which accounts for the associated duration of action of the respective toxin [8,35].

Bottom Line: However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified.By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics.This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

View Article: PubMed Central - PubMed

Affiliation: Department of Bacteriology, University of Wisconsin, 6340 Microbial Sciences Building, 1550 Linden Dr., Madison, WI 53706, USA. sabine.pellett@wisc.edu.

ABSTRACT
Current evidence suggests that botulinum neurotoxins (BoNTs) A1 and B1, given locally into peripheral tissues such as skin, muscles, and joints, alter nociceptive processing otherwise initiated by inflammation or nerve injury in animal models and humans. Recent data indicate that such locally delivered BoNTs exert not only local action on sensory afferent terminals but undergo transport to central afferent cell bodies (dorsal root ganglia) and spinal dorsal horn terminals, where they cleave SNAREs and block transmitter release. Increasing evidence supports the possibility of a trans-synaptic movement to alter postsynaptic function in neuronal and possibly non-neuronal (glial) cells. The vast majority of these studies have been conducted on BoNT/A1 and BoNT/B1, the only two pharmaceutically developed variants. However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified. By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics. This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

Show MeSH
Related in: MedlinePlus