Structure–function discrepancy inClostridium botulinumC3 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.

Structural constraints-based evaluation of immunogenic avirulent toxins from Clostridium botulinum C2 and C3 toxins as subunit vaccines

“…Coevolution resulted from the first point mutation may sometimes bring instability in the amino acid network structure of C2 and C3 toxins (Chellapandi et al, 2013;Chellapandi, 2014;Prathiviraj et al, 2015). We found no structural fluctuations in R299K, R300K, E389Q of C2I, G305K, E399A of C2II and E156D, E156Q, Q211A of C3 upon point mutations.…”

“…Several evolutionary constraints observed to be acted on the structure-function link of bacterial ADP-ribosyltransferases, particularly C2 and C3 toxins (Chellapandi et al, 2013;Chellapandi, 2014;Prathiviraj et al, 2015). Our study intensively described various structural constraints in the experimental mutants showing avirulent potential on the targets.…”

“…Cholera toxin A gene-mediated adjuvant was recently derived from a non-catalytic ADP-ribosyltransferase domain (Wan et al, 2014). The structure and function disparity of C3 toxins was recently provided a guidance to design rational-based subunit vaccines from avirulent mutants (Prathiviraj et al, 2015). However, no vaccine or immunotoxin has been generated for C2 and C3 toxins-mediated diseases in poultry and veterinary animals to date.…”

Identification of Genotypic Variants and its Proteomic mutations of Brazilian SARS-CoV-2 Isolates

“…The protein folding information plays a key role in the therapeutic intervention of many viral diseases (Broglia et al 2005;Prathiviraj et al, 2021). The folding process of a protein determines the structural stability and drug binding specificity (Prisilla et al, 2016;Prathiviraj et al, 2016) thus it's most important to identify the folding rate of mutants (Murugan et al, 2019;Prathiviraj et al, 2021). The protein folding rate among all the identified mutants was calculated using the FOLD-RATE server (Gromiha et al, 2006).…”

“…And slow fold rate was identified in other classes (All-α, α+β:α/β and unknown ). Hence, the fluctuation in protein folding leads to replication and multiplication of SARS-CoV-2 in the new environmental niche (Prisilla et al, 2016;Prathiviraj et al, 2016;Prathiviraj et al, 2021).…”