Ra. Li et al., Latent specificity of molecular recognition in sodium channels engineered to discriminate between two "indistinguishable'' mu-conotoxins, BIOCHEM, 40(20), 2001, pp. 6002-6008
mu -Conotoxins (mu -CTX) are potent oligopeptide blockers of sodium channel
s. The best characterized forms of mu -CTX, GIIIA and GIIIB, have similar p
rimary and three-dimensional structures and comparable potencies (IC50 simi
lar to 30 nM) for block of wild-type skeletal muscle Na+ channels. The two
toxins are thus considered to be indistinguishable by their target channels
. We have found mutations in the domain II pore region (D762K and E765K) th
at decrease GIIIB blocking affinity similar to 200-fold, but reduce GIIIA a
ffinity by only similar to4-fold, compared with wild-type channels. Synthet
ic CL-CTX GIIIA mutants reveal that the critical residue for differential r
ecognition is at position 14, the site of the only charge difference betwee
n the two toxin isoforms. Therefore, engineered Na+ channels, but not wild-
type channels, can discriminate between two highly homologous conotoxins. L
atent specificity of toxin-channel interactions, such as that revealed here
, is a principle worthy of exploitation in the design and construction of i
mproved biosensors.