Abstract
Four 0.5 kb full cobrotoxin (CBT) cDNAs encode for the same 62amino acid residues have been cloned and sequenced from venomglands of Naja naja atra, which are exactly identical to the oneidentified by the traditional protein sequencing methods byYang. In addition, a low abundant peptide, cobrotoxin-minor(CBT-m), was identified that belongs to the same family ascharacterizedby a common conserved tryptophan motif. CBT-mencodes for the 61 amino acidresidues, exhibited 13 amino acidsdifference and 79% sequence homology withcobrotoxins.Meanwhile, seventeen cardiotoxins (CTXs) and fourcardiotoxinlike basic proteins (CLBPs) have been identified fromthe same library, byscreening cDNA library and in conjunctionwith the PCR approach. Among the17 CTXs, two have silentsubstitutions, five have previously been identified bytraditional protein sequencing methods. In addition, ten notwell known CTX genes and one new CLBP have been identified.These CTX genes showvery high sequence homology with the majorvariations occuring at the tip ofeach individual loop. Althoughthe CTX isoforms differ by only one or fewresidues and thissubtle differences strongly influences the structure andfunction of the CTX isoforms. We have identified a novel CTX-3csequence whichrepresents a blend of the CTX-1 and CTX-3sequence. Based on the sequencecomparison with other CTXisoforms from the same snake source, we predict interestingfunctional properties for CTX-3c. All clones identified inthisstudy contain the same 21 residues of signal sequence.Phylogenetic analysisshowed that the CBTs/CBT-m and short NTXsfrom other elapid snakes were evolutionarily closedly related.