title: Structure-function discrepancy in Clostridium botulinum C3 toxin for its rational prioritization as a subunit vaccine.
abstract: Clostridium botulinum is anaerobic pathogenic bacterium causing food-born botulism in human and animals by producing botulinum neurotoxins A-H, C2, and C3 cytotoxins. Physiological group III strains (type C and D) of this bacterium are capable of producing C2 and C3 toxins in cattle and avian. Herein, we have revealed the structure-function disparity of C3 toxins from two different C. botulinum type C phage (CboC) and type D phage (CboD) to design avirulent toxins rationally. Structure-function discrepancy of the both toxins was computationally evaluated from their homology models based on the conservation in sequence-structure-function relationships upon covariation and point mutations. It has shown that 8 avirulent mutants were generated from CboC of 34 mutants while 27 avirulent mutants resulted from CboD mutants. No major changes were found in tertiary structure of these toxins; however, some structural variations appeared in the coiled and loop regions. Correlated mutation on the first residue would disorder or revolutionize the hydrogen bonding pattern of the coevolved pairs. It suggested that the residues coupling in the local structural environments were compensated with coevolved pairs so as to preserve a pseudocatalytic function in the avirulent mutants. Avirulent mutants of C3 toxins have shown a stable structure with a common blue print of folding process and also attained a near-native backrub ensemble. Thus, we concluded that selecting the site-directed mutagenesis sites are very important criteria for designing avirulent toxins, in development of rational subunit vaccines, to cattle and avian, but the vaccine specificity can be determined by the C3 toxins of C. botulinum harboring phages.
authors.affiliation: a Molecular Systems Engineering Lab, Department of Bioinformatics , School of Life Sciences, Bharathidasan University , Tiruchirappalli 620 024 , Tamil Nadu , India.
authors.forename: R
authors.initials: R
authors.lastname: Prathiviraj
authors.affiliation: a Molecular Systems Engineering Lab, Department of Bioinformatics , School of Life Sciences, Bharathidasan University , Tiruchirappalli 620 024 , Tamil Nadu , India.
authors.forename: A
authors.initials: A
authors.lastname: Prisilla
authors.affiliation: a Molecular Systems Engineering Lab, Department of Bioinformatics , School of Life Sciences, Bharathidasan University , Tiruchirappalli 620 024 , Tamil Nadu , India.
authors.forename: P
authors.initials: P
authors.lastname: Chellapandi
mesh_terms: D036002:ADP Ribose Transferases / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D000595:Amino Acid Sequence; D001905:Botulinum Toxins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D019143:Evolution, Molecular; D008958:Models, Molecular; D009154:Mutation; D059645:Mutation Rate; D011487:Protein Conformation; D017510:Protein Folding; D013329:Structure-Activity Relationship; D022223:Vaccines, Subunit / Q000276:immunology
chemical_list: D022223:Vaccines, Subunit; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins
keywords: ADP ribosyltransferase; C3 exoenzyme; binary toxins; molecular evolution; molecular pathogenesis; structure–function integrity; vaccine; virulence