sr-(Methionyl Cone Snail Mu-Conotoxin TIIIA) is a single chain protein produced by fermentation in E. coli. The starting gene is synthetically produced to be identical to Mu-conotoxin TIIIA which is found in the cone snail, Conus, with the initiation code for methionine. The protein contains 22 amino acids which may contain disulfide bonds and/or glycosylation, and consists of the proper sequence of the 20 standard amino acids.