The low molecular weight protein which co-purifies with alpha-latrotoxin is structurally related to crustacean...

LMWP is the low molecular weight protein which copurifies with alpha-latrotoxin, the main neurotoxin from the black widow venom. It contains 70 residues and three disulfides. We found that its primary structure, including its 6 half-cystines, can be aligned with the amino acid sequences of crustacean hyperglycemic hormones (CHHs) which contain 72-73 residues and three disulfides. To further investigate this structural relationship, we produced a recombinant analog of LMWP in which the unique Met was changed in Leu (LMWPM35L). LMWPM35L was produced as a folded fusion protein in the periplasm of Escherichia coli and was generated in vitro by treating the fusion protein with cyanogen bromide. We showed that LMWPM35L and CHHs have an identical disulfide pairing pattern and possess some alpha-helical structure, as deduced from a comparison of their circular dichroism spectra. In addition, LMWPM35L and CHHs are consensually predicted to possess a helical structure within the region 13-17. Together, the data indicate that CHHs are structurally related to LMWPM35L and presumably also to LMWP. Finally, preliminary studies showed that LMWPM35L is not toxic to mice and does not form channels in lipid bilayers, two well-known properties of alpha-latrotoxin preparations.