BOTULINAL NEUROTOXIN C1 COMPLEX GENES, CLOSTRIDIAL NEUROTOXIN HOMOLOGY AND GENETIC TRANSFER IN CLOSTRIDIUM-BOTULINUM

The botulinal neurotoxins (BoNT) associate with non-toxic proteins (AN TP) by non-covalent bonds to form large complexes. In C. botulinum C, the BoNT/C1 locus consists of six genes which are organized in three c lusters. Cluster 1 encompasses the genes of BoNT/C1 and ANTP/139 which could be involved in the resistance of the BoNT/C1 to the acidic pH a nd protease degradation. The second cluster consists of three genes wh ich encode hemagglutinin components. The last gene encodes a DNA bindi ng protein (Orf22) which might regulate the BoNT/C1 complex gene expre ssion. BoNT and tetanus toxin (TeTx) display similar structure and mec hanism of action at the molecular level. Their identity at the amino a cid level range from 34 to 96.8%, indicating that the clostridial neur otoxin genes probably derive from a common ancestor. The fact that Clo stridium other than C. botulinum such as C. butyricum and C. balata ca n produce a BoNT suggests that the BoNT genes can be transferred betwe en Clostridium strains. The toxigenic C. butyricum strains seem to der ive from originally non-toxic strains by neurotoxin gene transfer from C. botulinum E, probably including a mobile DNA element. In C. botuli num C and D the gene encoding the exoenzyme C3 has been localized in a transposon-like element of 21.5 kbp. Transposons could be involved in BoNT gene transfer in C. botulinum.