Primary Structure of Cholera Toxin β-Chain: A Glycoprotein Hormone Analog?

The completed sequence of the beta-chain of cholera toxin (103 amino acid residues) was compared to the beta-chains of chorionic gonadotropin, thyrotropin, luteinizing, and follicle stimulating hormones. The overall chemical similarity of the toxin beta-chain to the hormones was not statistically different from random; however, a comparison of the first 40 residues of the toxin beta-chain to the glycoprotein hormones revealed a segment of the hormones which was significantly chemically similar. The probability was less than .003 that the similarity was due to chance.