Maurotoxin

Maurotoxin (abbreviated MTX) is a peptide toxin from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus, from which it was first isolated and from which the chemical gets its name.

Maurotoxin is a peptide of 34 amino acids (sequence VSCTGSKDCYAPCRKQTGCPNAKCINKSCKCYGC) cross-linked by four disulfide bridges (Cys3-Cys24, Cys9-Cys29, Cys13-Cys19, Cys31-Cys34), with an atypical pattern of organization compared with other scorpion toxins; this unusual pairing of cysteine residues may be mediated by the presence of adjacent prolines.

The intermediate conductance Ca2+-activated K+ (IK) channel is present in peripheral tissues, including secretory epithelia and blood cells.

An important physiological role of the IK channel is to help maintain large electrical gradients for the sustained transport of ions such as Ca2+ that controls T lymphocyte (T cell) proliferation.

Thus IK blockers could be potential immunosuppressants for the treatment of autoimmune disorders (such as rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis).

The protein NMR structure of maurotoxin, illustrating the fluctuations in the protein's native state in solution. The protein backbone is shown in red, the alpha carbons of the eight cysteine residues in green, and the disulfide bridges in yellow. Compare the disulfide bond connectivity to HsTx1 below.
The protein NMR structure of HsTx1, a scorpion toxin with a canonical disulfide bond connectivity.