Scorpion venoms are complex mixtures of neurotoxins (low molecular weight
proteins), cardiotoxins, hemolytic toxins, antimicrobial peptides, enzymes
(such as hyaluronidase, acetylcholinesterase, phospholipase and
metalloproteinases), lipides, nucleotides, mucopolysaccharides and biogenic
amines. Neurotoxins can be classified as either short- or long-chain toxins,
which share a common structural motif, named CS-α/β for cysteine-stabilized α-helix/β-sheet. Short-chain neurotoxins (SCNs) usually
contain 30-40 residues and three or four disulphide bridges. Most of the short
chain toxins block voltage-dependent or Ca(2+)-activated K(+) channels. Most
long-chain neurotoxins (LCNs) are composed of 60-70 residues and are cross-linked by four disulphide bridges. The long chain or voltage-gated sodium
channels scorpion neurotoxins (NaScTxs) can be classified either as α-toxins, which slow down Na(+) channel inactivation, or β-toxins, which
affect the channel activation process. Both types make the inactivation of the
sodium channel incomplete [1,2,3]. Neurotoxins of the birtoxin family can be
included in the group of LCNs, although they possess three disulfide bridges
instead of the usual four disulfide bridges of other members of the group and
they are uniquely shorter than other LCNs [4,5].
The LCN-type CS-α/β domain consists of one or two short segments of
α-helix plus a triple-stranded β-sheet, connected by variable regions
forming loops (turns) (see <PDB:1B3C>) . The β-sheet and the α-helix
are held together by two disulfide bridges.
The profile we developed covers the entire LCN-type CS-α/β domain.
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