[Point mutation of the Virbrio cholerae O139 cef (CHO cell elongating factor) gene alters the substrate specificity of its product].

Sequencing of the cef (CHO cell elongating factor) of Vibrio cholerae serogroup O139 revealed one nucleotide substitution (C for T in position 2015) in comparison with classical V. cholerae O1 and two substitutions (AC for GT in positions 2014-2015) in comparison with V. cholerae O1 E1 Tor. A comparative bioinformatic analysis showed that the substitution determines a threonine residue in position 672 of the Cefprotein, while the position is occupied by an isoleucine residue in the classical strains and a valine residue in the El Tor group. The last two amino acids are hydrophobic, while threonine is hydrophilic, having a polar R group. The non- synonymous substitution affects the predicted secondary and, probably, tertiary structures of the Cef-O139 protein and explained our previous finding that the protein fails to degrade tributyrin, while retaining the tweenase activity spectrum and all other characteristics. It cannot be excluded that the inability of Cef-O139 to cleave triglycerides, along with other genetic specifics, contribute to the fact that the O139 serogroup has been displaced from a dominating position in etiology of cholera by the El Tor genotype. The nucleotide sequence of the V. cholerae O139 cefgene and the deduced amino acid sequence of its product are reported for the first time and were deposited in GenBank under accession nos. JF499787 and AEC04822.1, respectively.