Cytotoxic Peptides Are Small Proteins

Kourie, J. I., and A. A. Shorthouse. Properties of cytotoxic peptideformed ion channels. Am J Physiol Cell Physiol 278: C1063–C1087, 2000.—Cytotoxic peptides are relatively small cationic molecules such as those found 1) in venoms, e.g., melittin in bee, scorpion toxins in scorpion, pilosulin 1 in jumper ant, and lycotoxin I and II in wolf spider; 2) in skin secretions (e.g., magainin I and II from Xenopus laevis, dermaseptin from frog, antimicrobials from carp) and cells of the immune system (e.g., insect, scorpion, and mammalian defensins and cryptdins); 3) as autocytotoxicity peptides, e.g., amylin cytotoxic to pancreatic b-cells, prion peptide fragment 106–126 [PrP-(106–126)], and amyloid b-protein (AbP) cytotoxic to neurons; and 4) as designed synthetic peptides based on the sequences and properties of naturally occurring cytotoxic peptides. The small cytotoxic peptides are composed of b-sheets, e.g., mammalian defensins, AbP, amylin, and PrP-(106–126), whereas the larger cytotoxic peptides have several domains composed of both a-helices and b-sheets stabilized by cysteine bonds, e.g., scorpion toxins, scorpion, and insect defensins. Electrophysiological and molecular biology techniques indicate that these structures modify cell membranes via 1) interaction with intrinsic ion transport proteins and/or 2) formation of ion channels. These two nonexclusive mechanisms of action lead to changes in second messenger systems that further augment the abnormal electrical activity and distortion of the signal transduction causing cell death.