Domain Organization in Clostridium botulinum Neurotoxin Type E Is Unique: Its Implication in Faster Translocation

Biology Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Journal of Molecular Biology (Impact Factor: 4.33). 02/2009; 386(1):233-45. DOI: 10.1016/j.jmb.2008.12.027
Source: PubMed


Clostridium botulinum produces seven antigenically distinct neurotoxins [C. botulinum neurotoxins (BoNTs) A-G] sharing a significant sequence homology. Based on sequence and functional similarity, it was believed that their three-dimensional structures will also be similar. Indeed, the crystal structures of BoNTs A and B exhibit similar fold and domain association where the translocation domain is flanked on either side by binding and catalytic domains. Here, we report the crystal structure of BoNT E holotoxin and show that the domain association is different and unique, although the individual domains are similar to those of BoNTs A and B. In BoNT E, both the binding domain and the catalytic domain are on the same side of the translocation domain, and all three have mutual interfaces. This unique association may have an effect on the rate of translocation, with the molecule strategically positioned in the vesicle for quick entry into cytosol. Botulism, the disease caused by BoNT E, sets in faster than any other serotype because of its speedy internalization and translocation, and the present structure offers a credible explanation. We propose that the translocation domain in other BoNTs follows a two-step process to attain translocation-competent conformation as in BoNT E. We also suggest that this translocation-competent conformation in BoNT E is a probable reason for its faster toxic rate compared to BoNT A. However, this needs further experimental elucidation.

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    • "They consist of a light chain (L, 50 kDa) and a heavy chain (H, 100 kDa) linked by a strictly conserved interchain disulfide bond. Figure 1 shows the crystal structures of BoNT/A1 and of BoNT/E1; BoNT/B1 is very similar to BoNT/A1 (not shown) [10] [11] [12]. They consist of four domains: HC-C (25 kDa, in green in figure 1) involved in nerve terminal binding; HC-N (25 kDa purple in figure 1) of unknown function, though there is evidence that it binds to membrane lipids [13] [14]; L (red in fig. "
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    ABSTRACT: Tetanus and botulinum neurotoxins are produced by anaerobic bacteria of the genus Clostridium and are the most poisonous toxins known, with 50% mouse lethal dose comprised within the range 0.1 - few nanograms per Kg, depending on the individual toxin. Botulinum neurotoxins are similarly toxic to humans and can therefore be considered for potential use in bioterrorism. At the same time, their neurospecificity and reversibility of action makes them excellent therapeutics for a growing and heterogeneous number of human diseases that are characterized by a hyperactivity of peripheral nerve terminals. The complete crystallographic structure is available for some botulinum toxins, and reveals that they consist of four domains functionally related to the four steps of their mechanism of neuron intoxication: 1) binding to specific receptors of the presynaptic membrane; 2) internalization via endocytic vesicles; 3) translocation across the membrane of endocytic vesicles into the neuronal cytosol; 4) catalytic activity of the enzymatic moiety directed towards the SNARE proteins. Despite the many advances in understanding the structure-mechanism relationship of tetanus and botulinum neurotoxins, the molecular events involved in the translocation step have been only partially elucidated. Here we will review recent advances that have provided relevant insights on the process and discuss possible models that can be experimentally tested. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 08/2015; DOI:10.1016/j.bbamem.2015.08.014 · 4.66 Impact Factor
    • "Under trade names including Botox Cosmetics (USA), Vistabel (Europe), Azzalure, and Bocouture, BoNT/A is in popular use for cosmetic applications (Evidente and Adler, 2010; Markey, 2000). All BoNTs comprise a protease domain (LC), a translocation domain (H N ) and a receptor-binding domain (H C ) (Montal, 2010; Rossetto et al., 2014; Swaminathan, 2011), but there can be differences in the structural organization of the domains, as was shown for example for serotype E (Kumaran et al., 2009). In the maturation process of the toxin, the original single polypeptide chain is proteolytically cleaved into two parts. "
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    ABSTRACT: Botulinum neurotoxin A causes botulism but is also used for medical and cosmetic applications. A detailed molecular understanding of BoNT/A - host receptor interactions is therefore fundamental for improving current clinical applications and for developing new medical strategies targeting human disorders. Towards this end, we recently solved an X-ray crystal structure of BoNT/A1 in complex with its neuronal protein receptor SV2C. Based on our findings, we discuss the potential implications for BoNT/A function. Copyright © 2015. Published by Elsevier Ltd.
    Toxicon 08/2015; DOI:10.1016/j.toxicon.2015.08.002 · 2.49 Impact Factor
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    • "Despite of existence of a high number of isoforms, all BoNTs are structurally similar and consist of two chains linked by a unique disulphide bond: a light chain (L, 50 kDa) and a heavy chain (H, 100 kDa). The complete crystallographic structures of three BoNTs (A1, B1 and E1) (Lacy et al., 1998; Swaminathan and Eswaramoorthy, 2000; Kumaran et al., 2009; Montal, 2010) reveal different domains, which are functionally linked to the four steps of the mechanism of neuron intoxication by BoNTs. 1) Binding: the C-terminal domain of the heavy chain (HC) is responsible for the neurospecific binding. Notwithstanding the major effort of many different laboratories in the world, the receptors of BoNT/C (and many toxin subtypes) have not been yet identified. "
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    ABSTRACT: Botulinum neurotoxins are produced by anaerobic spore-forming bacteria of the genus Clostridium in several dozens of variants that inactivate neurotransmitter release owing to their metalloprotease activity. This results in a persistent paralysis of peripheral nerve terminals known as botulism. They are the most potent toxins known and are classified as one of the six highest-risk threat agents of bioterrorism. Despite their high toxicity, two of them are used as valuable pharmaceutical for the therapy of many neurological and non-neurological disorders. Notwithstanding the many advances in our understanding of the genetics and structure of botulinum neurotoxins, there are still many gaps in knowledge of toxin mechanism of action that will be discussed here. Copyright © 2015. Published by Elsevier Ltd.
    Toxicon 07/2015; DOI:10.1016/j.toxicon.2015.07.002 · 2.49 Impact Factor
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